Repository: Khan/genqlient
Pull request #68 (2021-08-27 00:22:25)

Return clearer errors when __typename is missing
## Summary:
In practice, at Khan at least, this is easy to mess up when writing
mocks, because you write the mock by looking at the query, and the query
doesn't say it's asking for `__typename` (because genqlient
automatically adds that).  A sufficiently-smart mocking library might be
able to fix that, or detect it at least, but in any case, we can give a
clearer error.

I also removed an unrelated TODO that was done.

Issue: https://khanacademy.slack.com/archives/C01120CNCS0/p1630019788014000

## Test plan:
make check



Patch:
diff --git a/DESIGN.md b/DESIGN.md
index 84d7ce7..c7c2a52 100644
--- a/DESIGN.md
+++ b/DESIGN.md
@@ -110,13 +110,13 @@ We'll do something similar to Apollo's naming scheme.  Specifically:
 
 All of this may be configurable later.
 
-### How to support fragments and interfaces
+### How to represent interfaces
 
 Consider the following query (suppose that `a` returns interface type `I`, which may be implemented by either `T` or `U`):
 
 ```graphql
-query { a { __typename b ...f } }
-fragment f on T { c d }
+query { a { __typename b ...F } }
+fragment F on T { c d }
 ```
 
 Depending on whether the concrete type returned from `a` is `T`, we can get one of two result structures back:
@@ -128,7 +128,7 @@ Depending on whether the concrete type returned from `a` is `T`, we can get one
 
 The question is: how do we translate that to Go types?
 
-One natural option is to generate a Go type for every concrete GraphQL type the object might have, and simply inline all the fragments.  So here we would have
+**Go interfaces:** one natural option is to generate a Go type for every concrete GraphQL type the object might have, and simply inline or embed all the fragments.  So here we would have
 ```go
 type T struct{ B, C, D string }
 type U struct{ B string }
@@ -147,13 +147,18 @@ Response{A: T{B: "...", C: "...", D: "..."}}
 Response{A: U{B: "..."}}
 ```
 
-Optionally, we might define a getter-method `GetB() string` on `T` and `U`, and include it in `I`, so that if you only need `B` you don't need to type-switch.  We could also define methods `GetC() string` and `GetD() string`, and another interface
+We can also define a getter-method `GetB() string` on `T` and `U`, and include it in `I`, so that if you only need `B` you don't need to type-switch.  Or, if that's not enough, we can also define a common embedded struct corresponding to the interface, so you can extract and pass that around if you want:
+
 ```go
-type F interface { isF(); GetC() string; GetD() string }
+type IEmbed struct { B string }
+type T struct { IEmbed; C, D string }
+type U struct { IEmbed }
+type I interface { isI(); GetIEmbed() IEmbed }
 ```
-so that if you want to use the same fragment `f` to share code in several places, you can do that, because all of the relevant types will implement `F`.  To do that we'll have to have the type-names for fragment fields rooted at the fragment rather than at the query, which is probably preferable anyway since they are guaranteed to be the same for all spreads of the fragment.  (Or we can just do the methods, and let you define the interface, although you still have to root the type-names for the same reason.) 
 
-Another natural option, which looks more like the way `shurcooL/graphql` does things, is to generate a type for each fragment, and only fill in the relevant ones:
+Note that this option gives a few different ways to represent fragments specifically, discussed in the next section.
+
+**Fragment fields:** another natural option, which looks more like the way `shurcooL/graphql` does things, is to generate a type for each fragment, and only fill in the relevant ones:
 ```go
 type Response struct {
     A struct {
@@ -183,13 +188,13 @@ query { a { b } }
 using the same schema as above.  In the former approach, we still define three types (plus two receivers); and `resp.A` is still of an interface type; it might be either `T` or `U`.  In the latter approach, this looks just like any other query: `resp.A` is a `struct{ B string }`.  This has implications for how we use this data: the latter approach lets us just do `resp.A.B`, whereas the former requires we do a type-switch, or add a `GetB()` method to `I`, and do `resp.A.GetB()`.
 
 
-Pros of the first approach:
+**Pros of Go interfaces:**
 
 - it's the most natural translation of how GraphQL does things, and provides the clearest guarantees about what is set when, what is mutually exclusive, etc.
 - you always know what type you got back
 - you always know which fields are there -- you don't have to encode at the application level an assumption that if fragment A was defined, fragment B also will be, because all types that match A also match B
 
-Pros of the second approach:
+**Pros of fragment fields:**
 
 - the types are simpler, and allow the option of unnamed types
 - if you query an interface, but don't care about the types, just the shared fields, you don't even have to think about any of this stuff
@@ -197,7 +202,7 @@ Pros of the second approach:
 
 Note that both approaches require that we add `__typename` to every selection set which has fragments (unless the types match exactly).  This seems fine since Apollo client also does so for all selection sets.  We also need to define `UnmarshalJSON` on every type with fragment-spreads; in the former case Go doesn't know how to unmarshal into an interface type, while in the latter the Go type structure is too different from that of the JSON.  (Note that `shurcooL/graphql` actually has its own JSON-decoder to solve this problem.)
 
-A third non-approach is to simplify define all the fields on the same struct, with some optional:
+**Flatten everything:** a third non-approach is to simplify define all the fields on the same struct, with some optional:
 
 ```go
 type Response struct {
@@ -211,7 +216,7 @@ type Response struct {
 
 Apart from being semantically messy, this doesn't have a good way to handle the case where there are types with conflicting fields, e.g.
 
-```
+```graphql
 interface I {}
 type T implements I { f: Int }
 type U implements I { f: String }
@@ -226,15 +231,157 @@ query {
 
 What type is `resp.A.F`?  It has to be both `string` and `int`.
 
-In other libraries:
-- Apollo does basically option 1, except with TypeScript/Flow's better support for sum types.
-- GraphQL Code Generator does basically option 1 (except with sum types instead of interfaces), except with unnamed types.  It definitely generates some ugly types, even with TypeScript/Flow's better support for sum types!
-- Khan's mobile autogen basically does option 1 (again with unnamed types, and sum types).
+**In other libraries:**
+- Apollo does basically the interface approach, except with TypeScript/Flow's better support for sum types.
+- GraphQL Code Generator does basically the interface approach (except with sum types instead of interfaces), except with unnamed types.  It definitely generates some ugly types, even with TypeScript/Flow's better support for sum types!
+- Khan's mobile autogen basically does the interface approach (again with unnamed types, and sum types).
 - gqlgen doesn't have this problem; on the server, fragments and interfaces are handled entirely in the framework and need not even be visible in user-land.
-- shurcooL/graphql uses option 2.
-- protobuf has a similar problem, and uses basically option 1 in Go (even though in other languages it uses something more like option 3).
+- shurcooL/graphql uses fragment fields.
+- protobuf has a similar problem, and uses basically the interface approach in Go (even though in other languages it uses something more like flattening everything).
+
+**Decision:** In general, it seems like the GraphQL Way, and perhaps also the Go Way is to use Go interfaces; I've always found the way shurcooL/graphql handles this to be a bit strange.  So I think it has to be at least the default.  In principle we could allow both though, since fragment fields are legitimately convenient for some cases, especially if you are querying shared fields of interfaces or using fragments as a code-sharing mechanism, since using Go interfaces handles those only through getter methods (although see below).
+
+### How to support fragments
+
+The previous section leaves some parts of how we'll handle fragments ambiguous.  Even within the way it lays things out, we generally have two options for how to represent a fragment.  Consider a query
+
+```graphql
+query MyQuery { a { b ...F } }
+fragment F on T { c d }
+```
+
+We'll have some struct (potentially several structs, one per implementation) representing the type of the value of `a`.  We can handle the fragment one of two ways: we can either flatten it into that type, such that the code is equivalent to writing `query Q { a { b c d } }` (except that `c` and `d` might be included for only some implementations, if `a` returns an interface), or we can represent it as a separate type `F` and embed it in the relevant structs.  (Or it could be a named field of said structs, but this seems to have little benefit, and it's nice to be able to access fields without knowing what fragment they're on.)  When the spread itself is abstract, there are a few sub-cases of the embed option.
+
+To get more concrete, there are [four cases](https://spec.graphql.org/June2018/#sec-Fragment-spread-is-possible) depending on the types in question.  (In all cases below, the methods, and other potential implementations of the interfaces, are elided.  Note also that I'm not sure I got all the type-names right exactly as genqlient would, but they should match approximately.)
+
+**Object spread in object scope:** The simplest spread is when we have an object-typed fragment spread into an object-typed selection.  (The two object types must be the same.)  This is typically used as a code-sharing mechanism.
+
+```graphql
+type Query { a: A }
+type A { b: String, c: String, d: String }
+
+query MyQuery { a { b ...F } }
+fragment F on A { c d }
+```
+
+```go
+// flattened:
+type MyQueryA struct { B, C, D string }
+
+// embedded
+type MyQueryA struct { B string; F }
+type F struct { C, D string }
+```
+
+**Abstract spread in object scope:** We can also spread an interface-typed fragment into an object-typed selection, again as a code-sharing mechanism.  (The object must implement the interface.)
+
+```graphql
+type Query { a: A }
+type A implements I { b: String, c: String, d: String }
+interface I { c: String, d: String }
+
+query MyQuery { a { b ...F } }
+fragment F on I { c d }
+```
+
+```go
+// flattened:
+type MyQueryA struct { B, C, D string }
+
+// embedded:
+type MyQueryA struct { B string; FA }
+type F interface { isF(); GetC() string; GetD() string } // for code-sharing purposes
+type FA struct { C, D string } // implements F
+```
+
+**Object spread in abstract scope:** This is the most common spread, perhaps, where you spread an object-typed fragment into an interface-typed selection in order to request some fields defined on a particular implementation of the interface.  (Again the object must implement the interface.)
+
+```graphql
+type Query { a: I }
+type A implements I { b: String, c: String, d: String }
+type T implements I { b: String, u: String, v: String }
+interface I { b: String }
+
+query MyQuery { a { b ...F ...G } }
+fragment F on A { c d }
+fragment G on A { u v }
+```
+
+```go
+// flattened:
+type MyQueryAI interface { isMyQueryAI(); GetB() string }
+type MyQueryAIA struct { B, C, D string } // implements MyQueryAI
+type MyQueryAIT struct { B, U, V string } // implements MyQueryAI
+
+// embedded:
+type MyQueryAI interface { isMyQueryAI(); GetB() string }
+type MyQueryAIA struct { B string; F } // implements MyQueryAI
+type MyQueryAIT struct { B string; G } // implements MyQueryAI
+type F struct { C, D string }
+type G struct { U, V string }
+```
+
+**Abstract spread in abstract scope:** This is a sort of combination of the last two, where you spread one interface's fragment into another interface, and can be used for code-sharing and/or to conditionally request fields.  Perhaps surprisingly, this is legal any time the two interfaces share an implementation, and neither need implement the other; this means there are arguably four cases of spreading a fragment of type `I` into a scope of type `J`: `I = J` (similar to object-in-object), `I implements J` (similar to abstract-in-object), `J implements I` (similar to object-in-abstract), and none of the above (which is quite rare).
+
+```graphql
+type Query { a: I }
+type A implements I & J { b: String, c: String, d: String }
+type T implements I { b: String }
+type U implements J { c: String, d: String, v: String }
+interface I { b: String }
+interface J { c: String, d: String }
+
+query MyQuery { a { b ...F } }
+fragment F on J { c d }
+```
+
+```go
+// flattened:
+type MyQueryAI interface { isMyQueryAI(); GetB() string }
+type MyQueryAIA struct { B, C, D string } // implements MyQueryAI (and MyQueryAJ if generated)
+type MyQueryAIT struct { B }              // implements MyQueryAI
+
+// embedded:
+type MyQueryAI interface { isMyQueryAI(); GetB() string }
+type MyQueryAIA struct { B string; FA } // implements MyQueryAI
+type MyQueryAIT struct { B string } // implements MyQueryAI
+type F interface { isF(); GetC() string; GetD() string }
+type FA struct { C, D string } // implements F
+type FU struct { C, D string } // implements F (never used; might be omitted)
+// if I == J or I implements J, perhaps additionally:
+type MyQueryAI interface { isMyQueryAI(); GetB() string; F }
+```
+
+Note in this case a third non-approach is
+
+```go
+// does not work:
+type MyQueryAI interface { isMyQueryAI(); GetB() string }
+type MyQueryAIA struct { B string; F } // implements MyQueryAI
+type F struct { C, D string }
+```
+
+This doesn't work because the fragment F might itself embed other fragments of object type.
+
+**Inline and named fragments:** Another complication is that in each of these cases, the fragment might be inline (`... on T { ... }`) or defined (`...F` where `fragment F on T { ... }`).  The latter is useful for sharing code, whereas the former may be more preferable when we just want request fields from a particular type.  Note that inline fragments have no natural name of their own; in the embedding approach we'd need to generate one.  (This is extra awkward because there's no prohibition on having several inline fragments of the same type in the same selection, e.g. `{ ... on T { id }, ... on T { name } }`, so even adding the type-name doesn't produce a unique name.)
+
+**Pros of flattening:**
+
+- Makes for the simplest resulting types, by far; the fragment adds no further complexity to the types.
+- Especially a simplification when embedding abstract-typed fragments, since you don't have to go through an extra layer of interface when you already have a concrete type.
+- More efficient when multiple fragments spread into the same selection contain the same field: we need only store it once whereas embedding must copy it once for each fragment.  Also easier to use in the same case, since if you have both `val.FragmentOne.MyField` and `val.FragmentTwo.MyField`, you can't access either via `val.MyField`.  (Empirically in the Khan Academy codebase this appears to be quite rare.)
+- If you need to manually construct values of genqlient-generated types, flattening will be a lot easier, but I don't really recommend doing that.
+
+**Pros of embedding:**
+
+- Results in cleaner type-names, since each (named) fragment can act as its own "root" for naming purposes.  (In principle we could do this even when flattening, although it might read somewhat awkwardly.)
+- Much more usable for deduplication; if you spread the fragment in several places in your query you can write a function which accepts an `F`, and pass it any of the data.  (Again we might be able to get this benefit, awkwardly, when flattening by generating an interface corresponding to each fragment, assuming we are also rooting the type-names at the fragment.)
+- It's easier to tell what fields go where; the casework for abstract-in-abstract embeds gets somewhat complex.
+- Arguably the most philosophically faithful representation of the GraphQL types in Go.
+
+Note in principle we could apply some of those benefits 
 
-**Decision:** In general, it seems like the GraphQL Way, and perhaps also the Go Way is Option 1; I've always found the way shurcooL/graphql handles this to be a bit strange.  So I think it has to be at least the default.  In principle we could allow both though, since option 2 is legitimately convenient for some cases, especially if you are querying shared fields of interfaces or using fragments as a code-sharing mechanism, since option 1 handles those only through getter methods.
+**Decision:** There are pros and cons both ways here; in general it seems embedding is the most natural where your goal is deduplication, whereas flattening is best for inline fragments; for named fragments used only once there's maybe a slight benefit to flattening but it's not a big difference either way.  If we have to go with one or the other, probably flattening is better.  But I think the best thing, unless it turns out to be too much work to implement, is probably just to flatten inline fragments and embed named ones.  (In principle we could also have a flag flatten named fragments, if we find a need.)
 
 ## Configuration and runtime
 
diff --git a/example/genqlient.yaml b/example/genqlient.yaml
index ad57911..7ef0bc7 100644
--- a/example/genqlient.yaml
+++ b/example/genqlient.yaml
@@ -5,7 +5,10 @@ operations:
 - genqlient.graphql
 generated: generated.go
 
-# We map github's DateTime type to Go's time.Time (which conveniently already
-# defines MarshalJSON and UnmarshalJSON).
-scalars:
-  DateTime: time.Time
+# We bind github's DateTime scalar type to Go's time.Time (which conveniently
+# already defines MarshalJSON and UnmarshalJSON).  This means genqlient will
+# use time.Time when a query requests a DateTime, and is required for custom
+# scalars.
+bindings:
+  DateTime:
+    type: time.Time
diff --git a/generate/config.go b/generate/config.go
index 4a07910..7ea3fcf 100644
--- a/generate/config.go
+++ b/generate/config.go
@@ -65,13 +65,25 @@ type Config struct {
 	// TODO(#5): This is a bit broken, fix it.
 	ClientGetter string `yaml:"client_getter"`
 
-	// A map from GraphQL scalar type name to Go fully-qualified type name for
-	// the types to use for any custom or builtin scalars.  By default, builtin
-	// scalars are mapped to the obvious Go types (String and ID to string, Int
-	// to int, Float to float64, and Boolean to bool), but this setting will
-	// extend or override those mappings.  These types must define MarshalJSON
-	// and UnmarshalJSON methods, or otherwise be convertible to JSON.
-	Scalars map[string]string `yaml:"scalars"`
+	// A map from GraphQL type name to Go fully-qualified type name to override
+	// the Go type genqlient will use for this GraphQL type.
+	//
+	// This is primarily used for custom scalars, or to map builtin scalars to
+	// a nonstandard type.  By default, builtin scalars are mapped to the
+	// obvious Go types (String and ID to string, Int to int, Float to float64,
+	// and Boolean to bool), but this setting will extend or override those
+	// mappings.
+	//
+	// genqlient does not validate these types in any way; they must define
+	// whatever logic is needed (MarshalJSON/UnmarshalJSON or JSON tags) to
+	// convert to/from JSON.  For this reason, it's not recommended to use this
+	// setting to map object, interface, or union types, because nothing
+	// guarantees that the fields requested in the query match those present in
+	// the Go type.
+	//
+	// To get equivalent behavior in just one query, use @genqlient(bind: ...);
+	// see GenqlientDirective.Bind for more details.
+	Bindings map[string]*TypeBinding `yaml:"bindings"`
 
 	// Set to true to use features that aren't fully ready to use.
 	//
@@ -84,6 +96,16 @@ type Config struct {
 	configFilename string
 }
 
+// A TypeBinding represents a Go type to which genqlient will bind a particular
+// GraphQL type.  See Config.Bind, above, for more details.
+type TypeBinding struct {
+	// The fully-qualified name of the Go type to which to bind.  For example:
+	//	time.Time
+	//  map[string]interface{}
+	//	github.com/you/yourpkg/subpkg.MyType
+	Type string `yaml:"type"`
+}
+
 // baseDir returns the directory of the config-file (relative to which
 // all the other paths are resolved).
 func (c *Config) baseDir() string {
diff --git a/generate/convert.go b/generate/convert.go
index ca3701d..8d47117 100644
--- a/generate/convert.go
+++ b/generate/convert.go
@@ -53,7 +53,7 @@ func (g *generator) convertOperation(
 
 	goTyp, err := g.convertDefinition(
 		name, operation.Name, baseType, operation.Position,
-		operation.SelectionSet, queryOptions)
+		operation.SelectionSet, queryOptions, queryOptions)
 
 	if structType, ok := goTyp.(*goStructType); ok {
 		// Override the ordinary description; the GraphQL documentation for
@@ -140,6 +140,15 @@ func (g *generator) convertType(
 	selectionSet ast.SelectionSet,
 	options, queryOptions *GenqlientDirective,
 ) (goType, error) {
+	// We check for local bindings here, so that you can bind, say, a
+	// `[String!]` to a struct instead of a slice.  Global bindings can only
+	// bind GraphQL named types, at least for now.
+	localBinding := options.Bind
+	if localBinding != "" && localBinding != "-" {
+		goRef, err := g.addRef(localBinding)
+		return &goOpaqueType{goRef}, err
+	}
+
 	if typ.Elem != nil {
 		// Type is a list.
 		elem, err := g.convertType(
@@ -150,7 +159,7 @@ func (g *generator) convertType(
 	// If this is a builtin type or custom scalar, just refer to it.
 	def := g.schema.Types[typ.Name()]
 	goTyp, err := g.convertDefinition(
-		name, namePrefix, def, typ.Position, selectionSet, queryOptions)
+		name, namePrefix, def, typ.Position, selectionSet, options, queryOptions)
 
 	if options.GetPointer() {
 		// Whatever we get, wrap it in a pointer.  (Because of the way the
@@ -172,11 +181,16 @@ func (g *generator) convertDefinition(
 	def *ast.Definition,
 	pos *ast.Position,
 	selectionSet ast.SelectionSet,
-	queryOptions *GenqlientDirective,
+	options, queryOptions *GenqlientDirective,
 ) (goType, error) {
-	qualifiedGoName, ok := g.Config.Scalars[def.Name]
-	if ok {
-		goRef, err := g.addRef(qualifiedGoName)
+	// Check if we should use an existing type.  (This is usually true for
+	// GraphQL scalars, but we allow you to bind non-scalar types too, if you
+	// want, subject to the caveats described in Config.Bindings.)  Local
+	// bindings are checked in the caller (convertType) and never get here,
+	// unless the binding is "-" which means "ignore the global binding".
+	globalBinding, ok := g.Config.Bindings[def.Name]
+	if ok && options.Bind != "-" {
+		goRef, err := g.addRef(globalBinding.Type)
 		return &goOpaqueType{goRef}, err
 	}
 	goBuiltinName, ok := builtinTypes[def.Name]
@@ -186,38 +200,20 @@ func (g *generator) convertDefinition(
 
 	switch def.Kind {
 	case ast.Object:
+		fields, err := g.convertSelectionSet(
+			namePrefix, selectionSet, def, queryOptions)
+		if err != nil {
+			return nil, err
+		}
+
 		goType := &goStructType{
 			GoName:      name,
 			Description: def.Description,
 			GraphQLName: def.Name,
-			Fields:      make([]*goStructField, len(selectionSet)),
+			Fields:      fields,
 			Incomplete:  true,
 		}
 		g.typeMap[name] = goType
-
-		for i, selection := range selectionSet {
-			_, selectionDirective, err := g.parsePrecedingComment(
-				selection, selection.GetPosition())
-			if err != nil {
-				return nil, err
-			}
-			selectionOptions := queryOptions.merge(selectionDirective)
-
-			switch selection := selection.(type) {
-			case *ast.Field:
-				goType.Fields[i], err = g.convertField(
-					namePrefix, selection, selectionOptions, queryOptions)
-				if err != nil {
-					return nil, err
-				}
-			case *ast.FragmentSpread:
-				return nil, errorf(selection.Position, "not implemented: %T", selection)
-			case *ast.InlineFragment:
-				return nil, errorf(selection.Position, "not implemented: %T", selection)
-			default:
-				return nil, errorf(nil, "invalid selection type: %T", selection)
-			}
-		}
 		return goType, nil
 
 	case ast.InputObject:
@@ -256,38 +252,22 @@ func (g *generator) convertDefinition(
 		return goType, nil
 
 	case ast.Interface, ast.Union:
+		sharedFields, err := g.convertSelectionSet(
+			namePrefix, selectionSet, def, queryOptions)
+		if err != nil {
+			return nil, err
+		}
+
 		implementationTypes := g.schema.GetPossibleTypes(def)
 		goType := &goInterfaceType{
 			GoName:          name,
 			Description:     def.Description,
 			GraphQLName:     def.Name,
-			SharedFields:    make([]*goStructField, 0, len(selectionSet)),
+			SharedFields:    sharedFields,
 			Implementations: make([]*goStructType, len(implementationTypes)),
 		}
 		g.typeMap[name] = goType
 
-		// TODO(benkraft): This sorta-duplicates what we'll do in each
-		// implementation when it traverses the fields.  But they'll differ
-		// more once we support fragments; at that point we should figure out
-		// how to refactor.
-		for _, selection := range selectionSet {
-			field, ok := selection.(*ast.Field)
-			if !ok { // fragment/interface, not a shared field
-				continue
-			}
-			_, fieldDirective, err := g.parsePrecedingComment(field, field.GetPosition())
-			if err != nil {
-				return nil, err
-			}
-			fieldOptions := queryOptions.merge(fieldDirective)
-
-			goField, err := g.convertField(namePrefix, field, fieldOptions, queryOptions)
-			if err != nil {
-				return nil, err
-			}
-			goType.SharedFields = append(goType.SharedFields, goField)
-		}
-
 		for i, implDef := range implementationTypes {
 			// Note for shared fields we propagate forward the interface's
 			// name-prefix: that is, the implementations will have fields with
@@ -306,7 +286,7 @@ func (g *generator) convertDefinition(
 			// preprocessQueryDocument).  But in practice it doesn't really
 			// hurt, and would be extra work to avoid, so we just leave it.
 			implTyp, err := g.convertDefinition(
-				implName, namePrefix, implDef, pos, selectionSet, queryOptions)
+				implName, namePrefix, implDef, pos, selectionSet, options, queryOptions)
 			if err != nil {
 				return nil, err
 			}
@@ -335,14 +315,165 @@ func (g *generator) convertDefinition(
 		return goType, nil
 
 	case ast.Scalar:
+		// (If you had an entry in bindings, we would have returned it above.)
 		return nil, errorf(
-			pos, "unknown scalar %v: please add it to genqlient.yaml", def.Name)
+			pos, `unknown scalar %v: please add it to "bindings" in genqlient.yaml`, def.Name)
 	default:
 		return nil, errorf(pos, "unexpected kind: %v", def.Kind)
 	}
 }
 
-// convertField converts a single GraphQL operation-field into a GraphQL type.
+// convertSelectionSet converts a GraphQL selection-set into a list of
+// corresponding Go struct-fields (and their Go types)
+//
+// A selection-set is a list of fields within braces like `{ myField }`, as
+// appears at the toplevel of a query, in a field's sub-selections, or within
+// an inline or named fragment.
+//
+// containingTypedef is the type-def whose fields we are selecting, and may be
+// an object type or an interface type.  In the case of interfaces, we'll call
+// convertSelectionSet once for the interface, and once for each
+// implementation.
+func (g *generator) convertSelectionSet(
+	namePrefix string,
+	selectionSet ast.SelectionSet,
+	containingTypedef *ast.Definition,
+	queryOptions *GenqlientDirective,
+) ([]*goStructField, error) {
+	fields := make([]*goStructField, 0, len(selectionSet))
+	for _, selection := range selectionSet {
+		_, selectionDirective, err := g.parsePrecedingComment(
+			selection, selection.GetPosition())
+		if err != nil {
+			return nil, err
+		}
+		selectionOptions := queryOptions.merge(selectionDirective)
+
+		switch selection := selection.(type) {
+		case *ast.Field:
+			field, err := g.convertField(
+				namePrefix, selection, selectionOptions, queryOptions)
+			if err != nil {
+				return nil, err
+			}
+			fields = append(fields, field)
+		case *ast.FragmentSpread:
+			return nil, errorf(selection.Position, "not implemented: %T", selection)
+		case *ast.InlineFragment:
+			// (Note this will return nil, nil if the fragment doesn't apply to
+			// this type.)
+			fragmentFields, err := g.convertInlineFragment(
+				namePrefix, selection, containingTypedef, queryOptions)
+			if err != nil {
+				return nil, err
+			}
+			fields = append(fields, fragmentFields...)
+		default:
+			return nil, errorf(nil, "invalid selection type: %T", selection)
+		}
+	}
+
+	// We need to deduplicate, if you asked for
+	//	{ id, id, id, ... on SubType { id } }
+	// (which, yes, is legal) we'll treat that as just { id }.
+	uniqFields := make([]*goStructField, 0, len(selectionSet))
+	fieldNames := make(map[string]bool, len(selectionSet))
+	for _, field := range fields {
+		// GraphQL (and, effectively, JSON) requires that all fields with the
+		// same alias (JSON-name) must be the same (i.e. refer to the same
+		// field), so that's how we deduplicate.
+		if fieldNames[field.JSONName] {
+			// GraphQL (and, effectively, JSON) forbids you from having two
+			// fields with the same alias (JSON-name) that refer to different
+			// GraphQL fields.  But it does allow you to have the same field
+			// with different selections (subject to some additional rules).
+			// We say: that's too complicated! and allow duplicate fields
+			// only if they're "leaf" types (enum or scalar).
+			switch field.GoType.Unwrap().(type) {
+			case *goOpaqueType, *goEnumType:
+				// Leaf field; we can just deduplicate.
+				// Note GraphQL already guarantees that the conflicting field
+				// has scalar/enum type iff this field does:
+				// https://spec.graphql.org/draft/#SameResponseShape()
+				continue
+			case *goStructType, *goInterfaceType:
+				// TODO(benkraft): Keep track of the position of each
+				// selection, so we can put this error on the right line.
+				return nil, errorf(nil,
+					"genqlient doesn't allow duplicate fields with different selections "+
+						"(see https://github.com/Khan/genqlient/issues/64); "+
+						"duplicate field: %s.%s", containingTypedef.Name, field.JSONName)
+			default:
+				return nil, errorf(nil, "unexpected field-type: %T", field.GoType.Unwrap())
+			}
+		}
+		uniqFields = append(uniqFields, field)
+		fieldNames[field.JSONName] = true
+	}
+	return uniqFields, nil
+}
+
+// fragmentMatches returns true if the given fragment is "active" when applied
+// to the given type.
+//
+// "Active" here means "the fragment's fields will be returned on all objects
+// of the given type", which is true when the given type is or implements
+// the fragment's type.  This is distinct from the rules for when a fragment
+// spread is legal, which is true when the fragment would be active for *any*
+// of the concrete types the spread-context could have (see
+// https://spec.graphql.org/draft/#sec-Fragment-Spreads or DESIGN.md).
+//
+// containingTypedef is as described in convertInlineFragment, below.
+// fragmentTypedef is the definition of the fragment's type-condition, i.e. the
+// definition of MyType in a fragment `on MyType`.
+func fragmentMatches(containingTypedef, fragmentTypedef *ast.Definition) bool {
+	if containingTypedef.Name == fragmentTypedef.Name {
+		return true
+	}
+	for _, iface := range containingTypedef.Interfaces {
+		// Note we don't need to recurse into the interfaces here, because in
+		// GraphQL types must list all the interfaces they implement, including
+		// all types those interfaces implement [1].  Actually, at present
+		// gqlparser doesn't even support interfaces implementing other
+		// interfaces, but our code would handle that too.
+		// [1] https://spec.graphql.org/draft/#sec-Interfaces.Interfaces-Implementing-Interfaces
+		if iface == fragmentTypedef.Name {
+			return true
+		}
+	}
+	return false
+}
+
+// convertInlineFragment converts a single GraphQL inline fragment
+// (`... on MyType { myField }`) into Go struct-fields.
+//
+// containingTypedef is the type-def corresponding to the type into which we
+// are spreading; it may be either an interface type (when spreading into one)
+// or an object type (when writing the implementations of such an interface, or
+// when using an inline fragment in an object type which is rare).  If the
+// given fragment does not apply to that type, this function returns nil, nil.
+//
+// In general, we treat such fragments' fields as if they were fields of the
+// parent selection-set (except of course they are only included in types the
+// fragment matches); see DESIGN.md for more.
+func (g *generator) convertInlineFragment(
+	namePrefix string,
+	fragment *ast.InlineFragment,
+	containingTypedef *ast.Definition,
+	queryOptions *GenqlientDirective,
+) ([]*goStructField, error) {
+	// You might think fragmentTypedef would be fragment.ObjectDefinition, but
+	// actually that's the type into which the fragment is spread.
+	fragmentTypedef := g.schema.Types[fragment.TypeCondition]
+	if !fragmentMatches(containingTypedef, fragmentTypedef) {
+		return nil, nil
+	}
+	return g.convertSelectionSet(namePrefix, fragment.SelectionSet,
+		containingTypedef, queryOptions)
+}
+
+// convertField converts a single GraphQL operation-field into a Go
+// struct-field (and its type).
 //
 // Note that input-type fields are handled separately (inline in
 // convertDefinition), because they come from the type-definition, not the
diff --git a/generate/genqlient_directive.go b/generate/genqlient_directive.go
index ab78029..5abf8b4 100644
--- a/generate/genqlient_directive.go
+++ b/generate/genqlient_directive.go
@@ -63,6 +63,27 @@ type GenqlientDirective struct {
 	// pointer to save copies) or if you wish to distinguish between the Go
 	// zero value and null (for nullable fields).
 	Pointer *bool
+
+	// If set, this argument or field will use the given Go type instead of a
+	// genqlient-generated type.
+	//
+	// The value should be the fully-qualified type name to use for the field,
+	// for example:
+	//	time.Time
+	//	map[string]interface{}
+	//	[]github.com/you/yourpkg/subpkg.MyType
+	// Note that the type is the type of the whole field, e.g. if your field in
+	// GraphQL has type `[DateTime]`, you'd do
+	//	# @genqlient(bind: "[]time.Time")
+	// (But you're not required to; if you want to map to some type DateList,
+	// you can do that, as long as its UnmarshalJSON method can accept a list
+	// of datetimes.)
+	//
+	// See Config.Bindings for more details; this is effectively to a local
+	// version of that global setting and should be used with similar care.
+	// If set to "-", overrides any such global setting and uses a
+	// genqlient-generated type.
+	Bind string
 }
 
 func (dir *GenqlientDirective) GetOmitempty() bool { return dir.Omitempty != nil && *dir.Omitempty }
@@ -70,7 +91,6 @@ func (dir *GenqlientDirective) GetPointer() bool   { return dir.Pointer != nil &
 
 func setBool(dst **bool, v *ast.Value) error {
 	ei, err := v.Value(nil) // no vars allowed
-	// TODO: here and below, put positions on these errors
 	if err != nil {
 		return errorf(v.Position, "invalid boolean value %v: %v", v, err)
 	}
@@ -81,6 +101,18 @@ func setBool(dst **bool, v *ast.Value) error {
 	return errorf(v.Position, "expected boolean, got non-boolean value %T(%v)", ei, ei)
 }
 
+func setString(dst *string, v *ast.Value) error {
+	ei, err := v.Value(nil) // no vars allowed
+	if err != nil {
+		return errorf(v.Position, "invalid string value %v: %v", v, err)
+	}
+	if b, ok := ei.(string); ok {
+		*dst = b
+		return nil
+	}
+	return errorf(v.Position, "expected string, got non-string value %T(%v)", ei, ei)
+}
+
 func fromGraphQL(dir *ast.Directive) (*GenqlientDirective, error) {
 	if dir.Name != "genqlient" {
 		// Actually we just won't get here; we only get here if the line starts
@@ -99,6 +131,8 @@ func fromGraphQL(dir *ast.Directive) (*GenqlientDirective, error) {
 			err = setBool(&retval.Omitempty, arg.Value)
 		case "pointer":
 			err = setBool(&retval.Pointer, arg.Value)
+		case "bind":
+			err = setString(&retval.Bind, arg.Value)
 		default:
 			return nil, errorf(arg.Position, "unknown argument %v for @genqlient", arg.Name)
 		}
@@ -112,8 +146,12 @@ func fromGraphQL(dir *ast.Directive) (*GenqlientDirective, error) {
 func (dir *GenqlientDirective) validate(node interface{}) error {
 	switch node := node.(type) {
 	case *ast.OperationDefinition:
-		// Anything is valid on the entire operation; it will just apply to
-		// whatever it is relevant to.
+		if dir.Bind != "" {
+			return errorf(dir.pos, "bind may not be applied to the entire operation")
+		}
+
+		// Anything else is valid on the entire operation; it will just apply
+		// to whatever it is relevant to.
 		return nil
 	case *ast.VariableDefinition:
 		if dir.Omitempty != nil && node.Type.NonNull {
@@ -122,7 +160,7 @@ func (dir *GenqlientDirective) validate(node interface{}) error {
 		return nil
 	case *ast.Field:
 		if dir.Omitempty != nil {
-			return errorf(dir.pos, "omitempty is not appilcable to fields")
+			return errorf(dir.pos, "omitempty is not applicable to fields")
 		}
 		return nil
 	default:
@@ -138,6 +176,9 @@ func (dir *GenqlientDirective) merge(other *GenqlientDirective) *GenqlientDirect
 	if other.Pointer != nil {
 		retval.Pointer = other.Pointer
 	}
+	if other.Bind != "" {
+		retval.Bind = other.Bind
+	}
 	return &retval
 }
 
diff --git a/generate/types.go b/generate/types.go
index a5433da..f978385 100644
--- a/generate/types.go
+++ b/generate/types.go
@@ -46,8 +46,8 @@ var (
 )
 
 type (
-	// goOpaqueType represents a user-defined or builtin type, used to
-	// represent a GraphQL scalar.
+	// goOpaqueType represents a user-defined or builtin type, often used to
+	// represent a GraphQL scalar.  (See Config.Bindings for more context.)
 	goOpaqueType struct{ GoRef string }
 	// goSliceType represents the Go type []Elem, used to represent GraphQL
 	// list types.
diff --git a/generate/unmarshal.go.tmpl b/generate/unmarshal.go.tmpl
index 980d3b6..d91a7f6 100644
--- a/generate/unmarshal.go.tmpl
+++ b/generate/unmarshal.go.tmpl
@@ -85,7 +85,8 @@ func (v *{{.GoName}}) UnmarshalJSON(b []byte) error {
         err = __unmarshal{{$field.GoType.Unwrap.Reference}}(
             {{if $field.GoType.IsPointer}}*{{end}}target, raw)
         if err != nil {
-            return err
+            return fmt.Errorf(
+                "Unable to unmarshal {{$.GoName}}.{{$field.GoName}}: %w", err)
         }
         {{range $i := intRange $field.GoType.SliceDepth -}}
         }
diff --git a/generate/unmarshal_helper.go.tmpl b/generate/unmarshal_helper.go.tmpl
index 8916375..a2b721f 100644
--- a/generate/unmarshal_helper.go.tmpl
+++ b/generate/unmarshal_helper.go.tmpl
@@ -17,10 +17,15 @@ func __unmarshal{{.GoName}}(v *{{.GoName}}, m {{ref "encoding/json.RawMessage"}}
     switch tn.TypeName {
     {{range .Implementations -}}
     case "{{.GraphQLName}}":
-        {{/* TODO: handle repeated fields! */ -}}
         *v = new({{.GoName}})
         return {{ref "encoding/json.Unmarshal"}}(m, *v)
     {{end -}}
+    case "":
+        {{/* Likely if we're making a request to a mock server and the author
+             of the mock didn't know to add __typename, so give a special
+             error. */ -}}
+        return {{ref "fmt.Errorf"}}(
+            "Response was missing {{.GraphQLName}}.__typename")
     default:
         return {{ref "fmt.Errorf"}}(
             `Unexpected concrete type for {{.GoName}}: "%v"`, tn.TypeName)
diff --git a/internal/integration/generated.go b/internal/integration/generated.go
index 69e7250..c0fcb08 100644
--- a/internal/integration/generated.go
+++ b/internal/integration/generated.go
@@ -10,6 +10,253 @@ import (
 	"github.com/Khan/genqlient/graphql"
 )
 
+type Species string
+
+const (
+	SpeciesDog        Species = "DOG"
+	SpeciesCoelacanth Species = "COELACANTH"
+)
+
+// queryWithFragmentsBeingsAnimal includes the requested fields of the GraphQL type Animal.
+type queryWithFragmentsBeingsAnimal struct {
+	Typename string                             `json:"__typename"`
+	Id       string                             `json:"id"`
+	Name     string                             `json:"name"`
+	Hair     queryWithFragmentsBeingsHair       `json:"hair"`
+	Species  Species                            `json:"species"`
+	Owner    queryWithFragmentsBeingsOwnerBeing `json:"-"`
+}
+
+func (v *queryWithFragmentsBeingsAnimal) UnmarshalJSON(b []byte) error {
+
+	type queryWithFragmentsBeingsAnimalWrapper queryWithFragmentsBeingsAnimal
+
+	var firstPass struct {
+		*queryWithFragmentsBeingsAnimalWrapper
+		Owner json.RawMessage `json:"owner"`
+	}
+	firstPass.queryWithFragmentsBeingsAnimalWrapper = (*queryWithFragmentsBeingsAnimalWrapper)(v)
+
+	err := json.Unmarshal(b, &firstPass)
+	if err != nil {
+		return err
+	}
+
+	{
+		target := &v.Owner
+		raw := firstPass.Owner
+		err = __unmarshalqueryWithFragmentsBeingsOwnerBeing(
+			target, raw)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// queryWithFragmentsBeingsBeing includes the requested fields of the GraphQL interface Being.
+//
+// queryWithFragmentsBeingsBeing is implemented by the following types:
+// queryWithFragmentsBeingsUser
+// queryWithFragmentsBeingsAnimal
+//
+// The GraphQL type's documentation follows.
+//
+//
+type queryWithFragmentsBeingsBeing interface {
+	implementsGraphQLInterfacequeryWithFragmentsBeingsBeing()
+	// GetTypename returns the receiver's concrete GraphQL type-name (see interface doc for possible values).
+	GetTypename() string
+	// GetId returns the interface-field "id" from its implementation.
+	GetId() string
+	// GetName returns the interface-field "name" from its implementation.
+	GetName() string
+}
+
+func (v *queryWithFragmentsBeingsUser) implementsGraphQLInterfacequeryWithFragmentsBeingsBeing() {}
+
+// GetTypename is a part of, and documented with, the interface queryWithFragmentsBeingsBeing.
+func (v *queryWithFragmentsBeingsUser) GetTypename() string { return v.Typename }
+
+// GetId is a part of, and documented with, the interface queryWithFragmentsBeingsBeing.
+func (v *queryWithFragmentsBeingsUser) GetId() string { return v.Id }
+
+// GetName is a part of, and documented with, the interface queryWithFragmentsBeingsBeing.
+func (v *queryWithFragmentsBeingsUser) GetName() string { return v.Name }
+
+func (v *queryWithFragmentsBeingsAnimal) implementsGraphQLInterfacequeryWithFragmentsBeingsBeing() {}
+
+// GetTypename is a part of, and documented with, the interface queryWithFragmentsBeingsBeing.
+func (v *queryWithFragmentsBeingsAnimal) GetTypename() string { return v.Typename }
+
+// GetId is a part of, and documented with, the interface queryWithFragmentsBeingsBeing.
+func (v *queryWithFragmentsBeingsAnimal) GetId() string { return v.Id }
+
+// GetName is a part of, and documented with, the interface queryWithFragmentsBeingsBeing.
+func (v *queryWithFragmentsBeingsAnimal) GetName() string { return v.Name }
+
+func __unmarshalqueryWithFragmentsBeingsBeing(v *queryWithFragmentsBeingsBeing, m json.RawMessage) error {
+	if string(m) == "null" {
+		return nil
+	}
+
+	var tn struct {
+		TypeName string `json:"__typename"`
+	}
+	err := json.Unmarshal(m, &tn)
+	if err != nil {
+		return err
+	}
+
+	switch tn.TypeName {
+	case "User":
+		*v = new(queryWithFragmentsBeingsUser)
+		return json.Unmarshal(m, *v)
+	case "Animal":
+		*v = new(queryWithFragmentsBeingsAnimal)
+		return json.Unmarshal(m, *v)
+	default:
+		return fmt.Errorf(
+			`Unexpected concrete type for queryWithFragmentsBeingsBeing: "%v"`, tn.TypeName)
+	}
+}
+
+// queryWithFragmentsBeingsHair includes the requested fields of the GraphQL type BeingsHair.
+type queryWithFragmentsBeingsHair struct {
+	HasHair bool `json:"hasHair"`
+}
+
+// queryWithFragmentsBeingsOwnerAnimal includes the requested fields of the GraphQL type Animal.
+type queryWithFragmentsBeingsOwnerAnimal struct {
+	Typename string `json:"__typename"`
+	Id       string `json:"id"`
+	Name     string `json:"name"`
+}
+
+// queryWithFragmentsBeingsOwnerBeing includes the requested fields of the GraphQL interface Being.
+//
+// queryWithFragmentsBeingsOwnerBeing is implemented by the following types:
+// queryWithFragmentsBeingsOwnerUser
+// queryWithFragmentsBeingsOwnerAnimal
+//
+// The GraphQL type's documentation follows.
+//
+//
+type queryWithFragmentsBeingsOwnerBeing interface {
+	implementsGraphQLInterfacequeryWithFragmentsBeingsOwnerBeing()
+	// GetTypename returns the receiver's concrete GraphQL type-name (see interface doc for possible values).
+	GetTypename() string
+	// GetId returns the interface-field "id" from its implementation.
+	GetId() string
+	// GetName returns the interface-field "name" from its implementation.
+	GetName() string
+}
+
+func (v *queryWithFragmentsBeingsOwnerUser) implementsGraphQLInterfacequeryWithFragmentsBeingsOwnerBeing() {
+}
+
+// GetTypename is a part of, and documented with, the interface queryWithFragmentsBeingsOwnerBeing.
+func (v *queryWithFragmentsBeingsOwnerUser) GetTypename() string { return v.Typename }
+
+// GetId is a part of, and documented with, the interface queryWithFragmentsBeingsOwnerBeing.
+func (v *queryWithFragmentsBeingsOwnerUser) GetId() string { return v.Id }
+
+// GetName is a part of, and documented with, the interface queryWithFragmentsBeingsOwnerBeing.
+func (v *queryWithFragmentsBeingsOwnerUser) GetName() string { return v.Name }
+
+func (v *queryWithFragmentsBeingsOwnerAnimal) implementsGraphQLInterfacequeryWithFragmentsBeingsOwnerBeing() {
+}
+
+// GetTypename is a part of, and documented with, the interface queryWithFragmentsBeingsOwnerBeing.
+func (v *queryWithFragmentsBeingsOwnerAnimal) GetTypename() string { return v.Typename }
+
+// GetId is a part of, and documented with, the interface queryWithFragmentsBeingsOwnerBeing.
+func (v *queryWithFragmentsBeingsOwnerAnimal) GetId() string { return v.Id }
+
+// GetName is a part of, and documented with, the interface queryWithFragmentsBeingsOwnerBeing.
+func (v *queryWithFragmentsBeingsOwnerAnimal) GetName() string { return v.Name }
+
+func __unmarshalqueryWithFragmentsBeingsOwnerBeing(v *queryWithFragmentsBeingsOwnerBeing, m json.RawMessage) error {
+	if string(m) == "null" {
+		return nil
+	}
+
+	var tn struct {
+		TypeName string `json:"__typename"`
+	}
+	err := json.Unmarshal(m, &tn)
+	if err != nil {
+		return err
+	}
+
+	switch tn.TypeName {
+	case "User":
+		*v = new(queryWithFragmentsBeingsOwnerUser)
+		return json.Unmarshal(m, *v)
+	case "Animal":
+		*v = new(queryWithFragmentsBeingsOwnerAnimal)
+		return json.Unmarshal(m, *v)
+	default:
+		return fmt.Errorf(
+			`Unexpected concrete type for queryWithFragmentsBeingsOwnerBeing: "%v"`, tn.TypeName)
+	}
+}
+
+// queryWithFragmentsBeingsOwnerUser includes the requested fields of the GraphQL type User.
+type queryWithFragmentsBeingsOwnerUser struct {
+	Typename    string `json:"__typename"`
+	Id          string `json:"id"`
+	Name        string `json:"name"`
+	LuckyNumber int    `json:"luckyNumber"`
+}
+
+// queryWithFragmentsBeingsUser includes the requested fields of the GraphQL type User.
+type queryWithFragmentsBeingsUser struct {
+	Typename    string                       `json:"__typename"`
+	Id          string                       `json:"id"`
+	Name        string                       `json:"name"`
+	LuckyNumber int                          `json:"luckyNumber"`
+	Hair        queryWithFragmentsBeingsHair `json:"hair"`
+}
+
+// queryWithFragmentsResponse is returned by queryWithFragments on success.
+type queryWithFragmentsResponse struct {
+	Beings []queryWithFragmentsBeingsBeing `json:"-"`
+}
+
+func (v *queryWithFragmentsResponse) UnmarshalJSON(b []byte) error {
+
+	type queryWithFragmentsResponseWrapper queryWithFragmentsResponse
+
+	var firstPass struct {
+		*queryWithFragmentsResponseWrapper
+		Beings []json.RawMessage `json:"beings"`
+	}
+	firstPass.queryWithFragmentsResponseWrapper = (*queryWithFragmentsResponseWrapper)(v)
+
+	err := json.Unmarshal(b, &firstPass)
+	if err != nil {
+		return err
+	}
+
+	{
+		target := &v.Beings
+		raw := firstPass.Beings
+		*target = make(
+			[]queryWithFragmentsBeingsBeing,
+			len(raw))
+		for i, raw := range raw {
+			target := &(*target)[i]
+			err = __unmarshalqueryWithFragmentsBeingsBeing(
+				target, raw)
+			if err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
 // queryWithInterfaceListFieldBeingsAnimal includes the requested fields of the GraphQL type Animal.
 type queryWithInterfaceListFieldBeingsAnimal struct {
 	Typename string `json:"__typename"`
@@ -80,6 +327,9 @@ func __unmarshalqueryWithInterfaceListFieldBeingsBeing(v *queryWithInterfaceList
 	case "Animal":
 		*v = new(queryWithInterfaceListFieldBeingsAnimal)
 		return json.Unmarshal(m, *v)
+	case "":
+		return fmt.Errorf(
+			"Response was missing Being.__typename")
 	default:
 		return fmt.Errorf(
 			`Unexpected concrete type for queryWithInterfaceListFieldBeingsBeing: "%v"`, tn.TypeName)
@@ -124,7 +374,8 @@ func (v *queryWithInterfaceListFieldResponse) UnmarshalJSON(b []byte) error {
 			err = __unmarshalqueryWithInterfaceListFieldBeingsBeing(
 				target, raw)
 			if err != nil {
-				return err
+				return fmt.Errorf(
+					"Unable to unmarshal queryWithInterfaceListFieldResponse.Beings: %w", err)
 			}
 		}
 	}
@@ -201,6 +452,9 @@ func __unmarshalqueryWithInterfaceListPointerFieldBeingsBeing(v *queryWithInterf
 	case "Animal":
 		*v = new(queryWithInterfaceListPointerFieldBeingsAnimal)
 		return json.Unmarshal(m, *v)
+	case "":
+		return fmt.Errorf(
+			"Response was missing Being.__typename")
 	default:
 		return fmt.Errorf(
 			`Unexpected concrete type for queryWithInterfaceListPointerFieldBeingsBeing: "%v"`, tn.TypeName)
@@ -246,7 +500,8 @@ func (v *queryWithInterfaceListPointerFieldResponse) UnmarshalJSON(b []byte) err
 			err = __unmarshalqueryWithInterfaceListPointerFieldBeingsBeing(
 				*target, raw)
 			if err != nil {
-				return err
+				return fmt.Errorf(
+					"Unable to unmarshal queryWithInterfaceListPointerFieldResponse.Beings: %w", err)
 			}
 		}
 	}
@@ -316,6 +571,9 @@ func __unmarshalqueryWithInterfaceNoFragmentsBeing(v *queryWithInterfaceNoFragme
 	case "Animal":
 		*v = new(queryWithInterfaceNoFragmentsBeingAnimal)
 		return json.Unmarshal(m, *v)
+	case "":
+		return fmt.Errorf(
+			"Response was missing Being.__typename")
 	default:
 		return fmt.Errorf(
 			`Unexpected concrete type for queryWithInterfaceNoFragmentsBeing: "%v"`, tn.TypeName)
@@ -369,7 +627,8 @@ func (v *queryWithInterfaceNoFragmentsResponse) UnmarshalJSON(b []byte) error {
 		err = __unmarshalqueryWithInterfaceNoFragmentsBeing(
 			target, raw)
 		if err != nil {
-			return err
+			return fmt.Errorf(
+				"Unable to unmarshal queryWithInterfaceNoFragmentsResponse.Being: %w", err)
 		}
 	}
 	return nil
@@ -537,3 +796,59 @@ query queryWithInterfaceListPointerField ($ids: [ID!]!) {
 	)
 	return &retval, err
 }
+
+func queryWithFragments(
+	ctx context.Context,
+	client graphql.Client,
+	ids []string,
+) (*queryWithFragmentsResponse, error) {
+	variables := map[string]interface{}{
+		"ids": ids,
+	}
+
+	var retval queryWithFragmentsResponse
+	err := client.MakeRequest(
+		ctx,
+		"queryWithFragments",
+		`
+query queryWithFragments ($ids: [ID!]!) {
+	beings(ids: $ids) {
+		__typename
+		id
+		... on Being {
+			id
+			name
+		}
+		... on Animal {
+			id
+			hair {
+				hasHair
+			}
+			species
+			owner {
+				__typename
+				id
+				... on Being {
+					name
+				}
+				... on User {
+					luckyNumber
+				}
+			}
+		}
+		... on Lucky {
+			luckyNumber
+		}
+		... on User {
+			hair {
+				color
+			}
+		}
+	}
+}
+`,
+		&retval,
+		variables,
+	)
+	return &retval, err
+}
diff --git a/internal/integration/schema.graphql b/internal/integration/schema.graphql
index 5c42e46..de6d3f5 100644
--- a/internal/integration/schema.graphql
+++ b/internal/integration/schema.graphql
@@ -3,21 +3,28 @@ type Query {
   user(id: ID!): User
   being(id: ID!): Being
   beings(ids: [ID!]!): [Being]!
+  lotteryWinner(number: Int!): Lucky
 }
 
-type User implements Being {
+type User implements Being & Lucky {
   id: ID!
   name: String!
   luckyNumber: Int
+  hair: Hair
 }
 
+type Hair { color: String }   # silly name to confuse the name-generator
+
 type Animal implements Being {
   id: ID!
   name: String!
   species: Species!
   owner: Being
+  hair: BeingsHair
 }
 
+type BeingsHair { hasHair: Boolean! }   # silly name to confuse the name-generator
+
 enum Species {
   DOG
   COELACANTH
@@ -27,3 +34,7 @@ interface Being {
   id: ID!
   name: String!
 }
+
+interface Lucky {
+  luckyNumber: Int
+}
diff --git a/internal/integration/server/gqlgen_exec.go b/internal/integration/server/gqlgen_exec.go
index d50db5a..709824f 100644
--- a/internal/integration/server/gqlgen_exec.go
+++ b/internal/integration/server/gqlgen_exec.go
@@ -43,20 +43,31 @@ type DirectiveRoot struct {
 
 type ComplexityRoot struct {
 	Animal struct {
+		Hair    func(childComplexity int) int
 		ID      func(childComplexity int) int
 		Name    func(childComplexity int) int
 		Owner   func(childComplexity int) int
 		Species func(childComplexity int) int
 	}
 
+	BeingsHair struct {
+		HasHair func(childComplexity int) int
+	}
+
+	Hair struct {
+		Color func(childComplexity int) int
+	}
+
 	Query struct {
-		Being  func(childComplexity int, id string) int
-		Beings func(childComplexity int, ids []string) int
-		Me     func(childComplexity int) int
-		User   func(childComplexity int, id string) int
+		Being         func(childComplexity int, id string) int
+		Beings        func(childComplexity int, ids []string) int
+		LotteryWinner func(childComplexity int, number int) int
+		Me            func(childComplexity int) int
+		User          func(childComplexity int, id string) int
 	}
 
 	User struct {
+		Hair        func(childComplexity int) int
 		ID          func(childComplexity int) int
 		LuckyNumber func(childComplexity int) int
 		Name        func(childComplexity int) int
@@ -68,6 +79,7 @@ type QueryResolver interface {
 	User(ctx context.Context, id string) (*User, error)
 	Being(ctx context.Context, id string) (Being, error)
 	Beings(ctx context.Context, ids []string) ([]Being, error)
+	LotteryWinner(ctx context.Context, number int) (Lucky, error)
 }
 
 type executableSchema struct {
@@ -85,6 +97,13 @@ func (e *executableSchema) Complexity(typeName, field string, childComplexity in
 	_ = ec
 	switch typeName + "." + field {
 
+	case "Animal.hair":
+		if e.complexity.Animal.Hair == nil {
+			break
+		}
+
+		return e.complexity.Animal.Hair(childComplexity), true
+
 	case "Animal.id":
 		if e.complexity.Animal.ID == nil {
 			break
@@ -113,6 +132,20 @@ func (e *executableSchema) Complexity(typeName, field string, childComplexity in
 
 		return e.complexity.Animal.Species(childComplexity), true
 
+	case "BeingsHair.hasHair":
+		if e.complexity.BeingsHair.HasHair == nil {
+			break
+		}
+
+		return e.complexity.BeingsHair.HasHair(childComplexity), true
+
+	case "Hair.color":
+		if e.complexity.Hair.Color == nil {
+			break
+		}
+
+		return e.complexity.Hair.Color(childComplexity), true
+
 	case "Query.being":
 		if e.complexity.Query.Being == nil {
 			break
@@ -137,6 +170,18 @@ func (e *executableSchema) Complexity(typeName, field string, childComplexity in
 
 		return e.complexity.Query.Beings(childComplexity, args["ids"].([]string)), true
 
+	case "Query.lotteryWinner":
+		if e.complexity.Query.LotteryWinner == nil {
+			break
+		}
+
+		args, err := ec.field_Query_lotteryWinner_args(context.TODO(), rawArgs)
+		if err != nil {
+			return 0, false
+		}
+
+		return e.complexity.Query.LotteryWinner(childComplexity, args["number"].(int)), true
+
 	case "Query.me":
 		if e.complexity.Query.Me == nil {
 			break
@@ -156,6 +201,13 @@ func (e *executableSchema) Complexity(typeName, field string, childComplexity in
 
 		return e.complexity.Query.User(childComplexity, args["id"].(string)), true
 
+	case "User.hair":
+		if e.complexity.User.Hair == nil {
+			break
+		}
+
+		return e.complexity.User.Hair(childComplexity), true
+
 	case "User.id":
 		if e.complexity.User.ID == nil {
 			break
@@ -232,21 +284,28 @@ var sources = []*ast.Source{
   user(id: ID!): User
   being(id: ID!): Being
   beings(ids: [ID!]!): [Being]!
+  lotteryWinner(number: Int!): Lucky
 }
 
-type User implements Being {
+type User implements Being & Lucky {
   id: ID!
   name: String!
   luckyNumber: Int
+  hair: Hair
 }
 
+type Hair { color: String }   # silly name to confuse the name-generator
+
 type Animal implements Being {
   id: ID!
   name: String!
   species: Species!
   owner: Being
+  hair: BeingsHair
 }
 
+type BeingsHair { hasHair: Boolean! }   # silly name to confuse the name-generator
+
 enum Species {
   DOG
   COELACANTH
@@ -256,6 +315,10 @@ interface Being {
   id: ID!
   name: String!
 }
+
+interface Lucky {
+  luckyNumber: Int
+}
 `, BuiltIn: false},
 }
 var parsedSchema = gqlparser.MustLoadSchema(sources...)
@@ -309,6 +372,21 @@ func (ec *executionContext) field_Query_beings_args(ctx context.Context, rawArgs
 	return args, nil
 }
 
+func (ec *executionContext) field_Query_lotteryWinner_args(ctx context.Context, rawArgs map[string]interface{}) (map[string]interface{}, error) {
+	var err error
+	args := map[string]interface{}{}
+	var arg0 int
+	if tmp, ok := rawArgs["number"]; ok {
+		ctx := graphql.WithPathContext(ctx, graphql.NewPathWithField("number"))
+		arg0, err = ec.unmarshalNInt2int(ctx, tmp)
+		if err != nil {
+			return nil, err
+		}
+	}
+	args["number"] = arg0
+	return args, nil
+}
+
 func (ec *executionContext) field_Query_user_args(ctx context.Context, rawArgs map[string]interface{}) (map[string]interface{}, error) {
 	var err error
 	args := map[string]interface{}{}
@@ -499,6 +577,105 @@ func (ec *executionContext) _Animal_owner(ctx context.Context, field graphql.Col
 	return ec.marshalOBeing2githubᚗcomᚋKhanᚋgenqlientᚋinternalᚋintegrationᚋserverᚐBeing(ctx, field.Selections, res)
 }
 
+func (ec *executionContext) _Animal_hair(ctx context.Context, field graphql.CollectedField, obj *Animal) (ret graphql.Marshaler) {
+	defer func() {
+		if r := recover(); r != nil {
+			ec.Error(ctx, ec.Recover(ctx, r))
+			ret = graphql.Null
+		}
+	}()
+	fc := &graphql.FieldContext{
+		Object:     "Animal",
+		Field:      field,
+		Args:       nil,
+		IsMethod:   false,
+		IsResolver: false,
+	}
+
+	ctx = graphql.WithFieldContext(ctx, fc)
+	resTmp, err := ec.ResolverMiddleware(ctx, func(rctx context.Context) (interface{}, error) {
+		ctx = rctx // use context from middleware stack in children
+		return obj.Hair, nil
+	})
+	if err != nil {
+		ec.Error(ctx, err)
+		return graphql.Null
+	}
+	if resTmp == nil {
+		return graphql.Null
+	}
+	res := resTmp.(*BeingsHair)
+	fc.Result = res
+	return ec.marshalOBeingsHair2ᚖgithubᚗcomᚋKhanᚋgenqlientᚋinternalᚋintegrationᚋserverᚐBeingsHair(ctx, field.Selections, res)
+}
+
+func (ec *executionContext) _BeingsHair_hasHair(ctx context.Context, field graphql.CollectedField, obj *BeingsHair) (ret graphql.Marshaler) {
+	defer func() {
+		if r := recover(); r != nil {
+			ec.Error(ctx, ec.Recover(ctx, r))
+			ret = graphql.Null
+		}
+	}()
+	fc := &graphql.FieldContext{
+		Object:     "BeingsHair",
+		Field:      field,
+		Args:       nil,
+		IsMethod:   false,
+		IsResolver: false,
+	}
+
+	ctx = graphql.WithFieldContext(ctx, fc)
+	resTmp, err := ec.ResolverMiddleware(ctx, func(rctx context.Context) (interface{}, error) {
+		ctx = rctx // use context from middleware stack in children
+		return obj.HasHair, nil
+	})
+	if err != nil {
+		ec.Error(ctx, err)
+		return graphql.Null
+	}
+	if resTmp == nil {
+		if !graphql.HasFieldError(ctx, fc) {
+			ec.Errorf(ctx, "must not be null")
+		}
+		return graphql.Null
+	}
+	res := resTmp.(bool)
+	fc.Result = res
+	return ec.marshalNBoolean2bool(ctx, field.Selections, res)
+}
+
+func (ec *executionContext) _Hair_color(ctx context.Context, field graphql.CollectedField, obj *Hair) (ret graphql.Marshaler) {
+	defer func() {
+		if r := recover(); r != nil {
+			ec.Error(ctx, ec.Recover(ctx, r))
+			ret = graphql.Null
+		}
+	}()
+	fc := &graphql.FieldContext{
+		Object:     "Hair",
+		Field:      field,
+		Args:       nil,
+		IsMethod:   false,
+		IsResolver: false,
+	}
+
+	ctx = graphql.WithFieldContext(ctx, fc)
+	resTmp, err := ec.ResolverMiddleware(ctx, func(rctx context.Context) (interface{}, error) {
+		ctx = rctx // use context from middleware stack in children
+		return obj.Color, nil
+	})
+	if err != nil {
+		ec.Error(ctx, err)
+		return graphql.Null
+	}
+	if resTmp == nil {
+		return graphql.Null
+	}
+	res := resTmp.(*string)
+	fc.Result = res
+	return ec.marshalOString2ᚖstring(ctx, field.Selections, res)
+}
+
 func (ec *executionContext) _Query_me(ctx context.Context, field graphql.CollectedField) (ret graphql.Marshaler) {
 	defer func() {
 		if r := recover(); r != nil {
@@ -651,6 +828,45 @@ func (ec *executionContext) _Query_beings(ctx context.Context, field graphql.Col
 	return ec.marshalNBeing2ᚕgithubᚗcomᚋKhanᚋgenqlientᚋinternalᚋintegrationᚋserverᚐBeing(ctx, field.Selections, res)
 }
 
+func (ec *executionContext) _Query_lotteryWinner(ctx context.Context, field graphql.CollectedField) (ret graphql.Marshaler) {
+	defer func() {
+		if r := recover(); r != nil {
+			ec.Error(ctx, ec.Recover(ctx, r))
+			ret = graphql.Null
+		}
+	}()
+	fc := &graphql.FieldContext{
+		Object:     "Query",
+		Field:      field,
+		Args:       nil,
+		IsMethod:   true,
+		IsResolver: true,
+	}
+
+	ctx = graphql.WithFieldContext(ctx, fc)
+	rawArgs := field.ArgumentMap(ec.Variables)
+	args, err := ec.field_Query_lotteryWinner_args(ctx, rawArgs)
+	if err != nil {
+		ec.Error(ctx, err)
+		return graphql.Null
+	}
+	fc.Args = args
+	resTmp, err := ec.ResolverMiddleware(ctx, func(rctx context.Context) (interface{}, error) {
+		ctx = rctx // use context from middleware stack in children
+		return ec.resolvers.Query().LotteryWinner(rctx, args["number"].(int))
+	})
+	if err != nil {
+		ec.Error(ctx, err)
+		return graphql.Null
+	}
+	if resTmp == nil {
+		return graphql.Null
+	}
+	res := resTmp.(Lucky)
+	fc.Result = res
+	return ec.marshalOLucky2githubᚗcomᚋKhanᚋgenqlientᚋinternalᚋintegrationᚋserverᚐLucky(ctx, field.Selections, res)
+}
+
 func (ec *executionContext) _Query___type(ctx context.Context, field graphql.CollectedField) (ret graphql.Marshaler) {
 	defer func() {
 		if r := recover(); r != nil {
@@ -824,6 +1040,38 @@ func (ec *executionContext) _User_luckyNumber(ctx context.Context, field graphql
 	return ec.marshalOInt2ᚖint(ctx, field.Selections, res)
 }
 
+func (ec *executionContext) _User_hair(ctx context.Context, field graphql.CollectedField, obj *User) (ret graphql.Marshaler) {
+	defer func() {
+		if r := recover(); r != nil {
+			ec.Error(ctx, ec.Recover(ctx, r))
+			ret = graphql.Null
+		}
+	}()
+	fc := &graphql.FieldContext{
+		Object:     "User",
+		Field:      field,
+		Args:       nil,
+		IsMethod:   false,
+		IsResolver: false,
+	}
+
+	ctx = graphql.WithFieldContext(ctx, fc)
+	resTmp, err := ec.ResolverMiddleware(ctx, func(rctx context.Context) (interface{}, error) {
+		ctx = rctx // use context from middleware stack in children
+		return obj.Hair, nil
+	})
+	if err != nil {
+		ec.Error(ctx, err)
+		return graphql.Null
+	}
+	if resTmp == nil {
+		return graphql.Null
+	}
+	res := resTmp.(*Hair)
+	fc.Result = res
+	return ec.marshalOHair2ᚖgithubᚗcomᚋKhanᚋgenqlientᚋinternalᚋintegrationᚋserverᚐHair(ctx, field.Selections, res)
+}
+
 func (ec *executionContext) ___Directive_name(ctx context.Context, field graphql.CollectedField, obj *introspection.Directive) (ret graphql.Marshaler) {
 	defer func() {
 		if r := recover(); r != nil {
@@ -1938,6 +2186,22 @@ func (ec *executionContext) _Being(ctx context.Context, sel ast.SelectionSet, ob
 	}
 }
 
+func (ec *executionContext) _Lucky(ctx context.Context, sel ast.SelectionSet, obj Lucky) graphql.Marshaler {
+	switch obj := (obj).(type) {
+	case nil:
+		return graphql.Null
+	case User:
+		return ec._User(ctx, sel, &obj)
+	case *User:
+		if obj == nil {
+			return graphql.Null
+		}
+		return ec._User(ctx, sel, obj)
+	default:
+		panic(fmt.Errorf("unexpected type %T", obj))
+	}
+}
+
 // endregion ************************** interface.gotpl ***************************
 
 // region    **************************** object.gotpl ****************************
@@ -1970,6 +2234,59 @@ func (ec *executionContext) _Animal(ctx context.Context, sel ast.SelectionSet, o
 			}
 		case "owner":
 			out.Values[i] = ec._Animal_owner(ctx, field, obj)
+		case "hair":
+			out.Values[i] = ec._Animal_hair(ctx, field, obj)
+		default:
+			panic("unknown field " + strconv.Quote(field.Name))
+		}
+	}
+	out.Dispatch()
+	if invalids > 0 {
+		return graphql.Null
+	}
+	return out
+}
+
+var beingsHairImplementors = []string{"BeingsHair"}
+
+func (ec *executionContext) _BeingsHair(ctx context.Context, sel ast.SelectionSet, obj *BeingsHair) graphql.Marshaler {
+	fields := graphql.CollectFields(ec.OperationContext, sel, beingsHairImplementors)
+
+	out := graphql.NewFieldSet(fields)
+	var invalids uint32
+	for i, field := range fields {
+		switch field.Name {
+		case "__typename":
+			out.Values[i] = graphql.MarshalString("BeingsHair")
+		case "hasHair":
+			out.Values[i] = ec._BeingsHair_hasHair(ctx, field, obj)
+			if out.Values[i] == graphql.Null {
+				invalids++
+			}
+		default:
+			panic("unknown field " + strconv.Quote(field.Name))
+		}
+	}
+	out.Dispatch()
+	if invalids > 0 {
+		return graphql.Null
+	}
+	return out
+}
+
+var hairImplementors = []string{"Hair"}
+
+func (ec *executionContext) _Hair(ctx context.Context, sel ast.SelectionSet, obj *Hair) graphql.Marshaler {
+	fields := graphql.CollectFields(ec.OperationContext, sel, hairImplementors)
+
+	out := graphql.NewFieldSet(fields)
+	var invalids uint32
+	for i, field := range fields {
+		switch field.Name {
+		case "__typename":
+			out.Values[i] = graphql.MarshalString("Hair")
+		case "color":
+			out.Values[i] = ec._Hair_color(ctx, field, obj)
 		default:
 			panic("unknown field " + strconv.Quote(field.Name))
 		}
@@ -2043,6 +2360,17 @@ func (ec *executionContext) _Query(ctx context.Context, sel ast.SelectionSet) gr
 				}
 				return res
 			})
+		case "lotteryWinner":
+			field := field
+			out.Concurrently(i, func() (res graphql.Marshaler) {
+				defer func() {
+					if r := recover(); r != nil {
+						ec.Error(ctx, ec.Recover(ctx, r))
+					}
+				}()
+				res = ec._Query_lotteryWinner(ctx, field)
+				return res
+			})
 		case "__type":
 			out.Values[i] = ec._Query___type(ctx, field)
 		case "__schema":
@@ -2058,7 +2386,7 @@ func (ec *executionContext) _Query(ctx context.Context, sel ast.SelectionSet) gr
 	return out
 }
 
-var userImplementors = []string{"User", "Being"}
+var userImplementors = []string{"User", "Being", "Lucky"}
 
 func (ec *executionContext) _User(ctx context.Context, sel ast.SelectionSet, obj *User) graphql.Marshaler {
 	fields := graphql.CollectFields(ec.OperationContext, sel, userImplementors)
@@ -2081,6 +2409,8 @@ func (ec *executionContext) _User(ctx context.Context, sel ast.SelectionSet, obj
 			}
 		case "luckyNumber":
 			out.Values[i] = ec._User_luckyNumber(ctx, field, obj)
+		case "hair":
+			out.Values[i] = ec._User_hair(ctx, field, obj)
 		default:
 			panic("unknown field " + strconv.Quote(field.Name))
 		}
@@ -2434,6 +2764,21 @@ func (ec *executionContext) marshalNID2ᚕstringᚄ(ctx context.Context, sel ast
 	return ret
 }
 
+func (ec *executionContext) unmarshalNInt2int(ctx context.Context, v interface{}) (int, error) {
+	res, err := graphql.UnmarshalInt(v)
+	return res, graphql.ErrorOnPath(ctx, err)
+}
+
+func (ec *executionContext) marshalNInt2int(ctx context.Context, sel ast.SelectionSet, v int) graphql.Marshaler {
+	res := graphql.MarshalInt(v)
+	if res == graphql.Null {
+		if !graphql.HasFieldError(ctx, graphql.GetFieldContext(ctx)) {
+			ec.Errorf(ctx, "must not be null")
+		}
+	}
+	return res
+}
+
 func (ec *executionContext) unmarshalNSpecies2githubᚗcomᚋKhanᚋgenqlientᚋinternalᚋintegrationᚋserverᚐSpecies(ctx context.Context, v interface{}) (Species, error) {
 	var res Species
 	err := res.UnmarshalGQL(v)
@@ -2695,6 +3040,13 @@ func (ec *executionContext) marshalOBeing2githubᚗcomᚋKhanᚋgenqlientᚋinte
 	return ec._Being(ctx, sel, v)
 }
 
+func (ec *executionContext) marshalOBeingsHair2ᚖgithubᚗcomᚋKhanᚋgenqlientᚋinternalᚋintegrationᚋserverᚐBeingsHair(ctx context.Context, sel ast.SelectionSet, v *BeingsHair) graphql.Marshaler {
+	if v == nil {
+		return graphql.Null
+	}
+	return ec._BeingsHair(ctx, sel, v)
+}
+
 func (ec *executionContext) unmarshalOBoolean2bool(ctx context.Context, v interface{}) (bool, error) {
 	res, err := graphql.UnmarshalBoolean(v)
 	return res, graphql.ErrorOnPath(ctx, err)
@@ -2719,6 +3071,13 @@ func (ec *executionContext) marshalOBoolean2ᚖbool(ctx context.Context, sel ast
 	return graphql.MarshalBoolean(*v)
 }
 
+func (ec *executionContext) marshalOHair2ᚖgithubᚗcomᚋKhanᚋgenqlientᚋinternalᚋintegrationᚋserverᚐHair(ctx context.Context, sel ast.SelectionSet, v *Hair) graphql.Marshaler {
+	if v == nil {
+		return graphql.Null
+	}
+	return ec._Hair(ctx, sel, v)
+}
+
 func (ec *executionContext) unmarshalOInt2ᚖint(ctx context.Context, v interface{}) (*int, error) {
 	if v == nil {
 		return nil, nil
@@ -2734,6 +3093,13 @@ func (ec *executionContext) marshalOInt2ᚖint(ctx context.Context, sel ast.Sele
 	return graphql.MarshalInt(*v)
 }
 
+func (ec *executionContext) marshalOLucky2githubᚗcomᚋKhanᚋgenqlientᚋinternalᚋintegrationᚋserverᚐLucky(ctx context.Context, sel ast.SelectionSet, v Lucky) graphql.Marshaler {
+	if v == nil {
+		return graphql.Null
+	}
+	return ec._Lucky(ctx, sel, v)
+}
+
 func (ec *executionContext) unmarshalOString2string(ctx context.Context, v interface{}) (string, error) {
 	res, err := graphql.UnmarshalString(v)
 	return res, graphql.ErrorOnPath(ctx, err)
diff --git a/internal/integration/server/gqlgen_models.go b/internal/integration/server/gqlgen_models.go
index a3318fe..a8b225b 100644
--- a/internal/integration/server/gqlgen_models.go
+++ b/internal/integration/server/gqlgen_models.go
@@ -12,22 +12,37 @@ type Being interface {
 	IsBeing()
 }
 
+type Lucky interface {
+	IsLucky()
+}
+
 type Animal struct {
-	ID      string  `json:"id"`
-	Name    string  `json:"name"`
-	Species Species `json:"species"`
-	Owner   Being   `json:"owner"`
+	ID      string      `json:"id"`
+	Name    string      `json:"name"`
+	Species Species     `json:"species"`
+	Owner   Being       `json:"owner"`
+	Hair    *BeingsHair `json:"hair"`
 }
 
 func (Animal) IsBeing() {}
 
+type BeingsHair struct {
+	HasHair bool `json:"hasHair"`
+}
+
+type Hair struct {
+	Color *string `json:"color"`
+}
+
 type User struct {
 	ID          string `json:"id"`
 	Name        string `json:"name"`
 	LuckyNumber *int   `json:"luckyNumber"`
+	Hair        *Hair  `json:"hair"`
 }
 
 func (User) IsBeing() {}
+func (User) IsLucky() {}
 
 type Species string
 
diff --git a/internal/integration/server/server.go b/internal/integration/server/server.go
index 8032326..6cff7cc 100644
--- a/internal/integration/server/server.go
+++ b/internal/integration/server/server.go
@@ -8,16 +8,26 @@ import (
 	"github.com/99designs/gqlgen/graphql/handler/transport"
 )
 
-func intptr(v int) *int { return &v }
+func strptr(v string) *string { return &v }
+func intptr(v int) *int       { return &v }
 
 var users = []*User{
-	{ID: "1", Name: "Yours Truly", LuckyNumber: intptr(17)},
-	{ID: "2", Name: "Raven", LuckyNumber: intptr(-1)},
+	{
+		ID: "1", Name: "Yours Truly", LuckyNumber: intptr(17),
+		Hair: &Hair{Color: strptr("Black")},
+	},
+	{ID: "2", Name: "Raven", LuckyNumber: intptr(-1), Hair: nil},
 }
 
 var animals = []*Animal{
-	{ID: "3", Name: "Fido", Species: SpeciesDog, Owner: userByID("0")},
-	{ID: "4", Name: "Old One", Species: SpeciesCoelacanth, Owner: nil},
+	{
+		ID: "3", Name: "Fido", Species: SpeciesDog, Owner: userByID("1"),
+		Hair: &BeingsHair{HasHair: true},
+	},
+	{
+		ID: "4", Name: "Old One", Species: SpeciesCoelacanth, Owner: nil,
+		Hair: &BeingsHair{HasHair: false},
+	},
 }
 
 func userByID(id string) *User {
@@ -63,6 +73,15 @@ func (r *queryResolver) Beings(ctx context.Context, ids []string) ([]Being, erro
 	return ret, nil
 }
 
+func (r *queryResolver) LotteryWinner(ctx context.Context, number int) (Lucky, error) {
+	for _, user := range users {
+		if user.LuckyNumber != nil && *user.LuckyNumber == number {
+			return user, nil
+		}
+	}
+	return nil, nil
+}
+
 func RunServer() *httptest.Server {
 	gqlgenServer := handler.New(NewExecutableSchema(Config{Resolvers: &resolver{}}))
 	gqlgenServer.AddTransport(transport.POST{})


Test patch:
diff --git a/generate/generate_test.go b/generate/generate_test.go
index f69f223..a909127 100644
--- a/generate/generate_test.go
+++ b/generate/generate_test.go
@@ -51,11 +51,13 @@ func TestGenerate(t *testing.T) {
 				Package:          "test",
 				Generated:        goFilename,
 				ExportOperations: queriesFilename,
-				Scalars: map[string]string{
-					"ID":          "github.com/Khan/genqlient/internal/testutil.ID",
-					"DateTime":    "time.Time",
-					"Junk":        "interface{}",
-					"ComplexJunk": "[]map[string]*[]*map[string]interface{}",
+				Bindings: map[string]*TypeBinding{
+					"ID":           {Type: "github.com/Khan/genqlient/internal/testutil.ID"},
+					"DateTime":     {Type: "time.Time"},
+					"Junk":         {Type: "interface{}"},
+					"ComplexJunk":  {Type: "[]map[string]*[]*map[string]interface{}"},
+					"Pokemon":      {Type: "github.com/Khan/genqlient/internal/testutil.Pokemon"},
+					"PokemonInput": {Type: "github.com/Khan/genqlient/internal/testutil.Pokemon"},
 				},
 				AllowBrokenFeatures: true,
 			})
@@ -138,9 +140,9 @@ func TestGenerateErrors(t *testing.T) {
 				Operations: []string{filepath.Join(errorsDir, sourceFilename)},
 				Package:    "test",
 				Generated:  os.DevNull,
-				Scalars: map[string]string{
-					"ValidScalar":   "string",
-					"InvalidScalar": "bogus",
+				Bindings: map[string]*TypeBinding{
+					"ValidScalar":   {Type: "string"},
+					"InvalidScalar": {Type: "bogus"},
 				},
 				AllowBrokenFeatures: true,
 			})
diff --git a/generate/testdata/errors/ConflictingSelections.go b/generate/testdata/errors/ConflictingSelections.go
new file mode 100644
index 0000000..c8ff6a3
--- /dev/null
+++ b/generate/testdata/errors/ConflictingSelections.go
@@ -0,0 +1,12 @@
+package errors
+
+const _ = `# @genqlient
+query {
+  myField {
+    subField { subSubField1 subSubField2 }
+    ... on OnePossibleConcreteType {
+      subField { subSubField3 subSubField4 }
+    }
+  }
+}
+`
diff --git a/generate/testdata/errors/ConflictingSelections.graphql b/generate/testdata/errors/ConflictingSelections.graphql
new file mode 100644
index 0000000..159624e
--- /dev/null
+++ b/generate/testdata/errors/ConflictingSelections.graphql
@@ -0,0 +1,8 @@
+query {
+  myField {
+    subField { subSubField1 subSubField2 }
+    ... on OnePossibleConcreteType {
+      subField { subSubField3 subSubField4 }
+    }
+  }
+}
diff --git a/generate/testdata/errors/ConflictingSelections.schema.graphql b/generate/testdata/errors/ConflictingSelections.schema.graphql
new file mode 100644
index 0000000..72ed539
--- /dev/null
+++ b/generate/testdata/errors/ConflictingSelections.schema.graphql
@@ -0,0 +1,18 @@
+type Query {
+  myField: InterfaceType
+}
+
+interface InterfaceType {
+  subField: SubFieldType
+}
+
+type OnePossibleConcreteType implements InterfaceType {
+  subField: SubFieldType
+}
+
+type SubFieldType {
+  subSubField1: String!
+  subSubField2: String!
+  subSubField3: String!
+  subSubField4: String!
+}
diff --git a/generate/testdata/queries/ComplexInlineFragments.graphql b/generate/testdata/queries/ComplexInlineFragments.graphql
new file mode 100644
index 0000000..99698f3
--- /dev/null
+++ b/generate/testdata/queries/ComplexInlineFragments.graphql
@@ -0,0 +1,69 @@
+# We test all the spread cases from DESIGN.md, see there for more context on
+# each, as well as various other nonsense.  But for abstract-in-abstract
+# spreads, we can't test cases (4b) and (4c), where I implements J or vice
+# versa, because gqlparser doesn't support interfaces that implement other
+# interfaces yet.
+query ComplexInlineFragments {
+  root {
+    id
+    ... on Topic { schoolGrade }  # (1) object spread in object scope
+    ... on Content { name }       # (3) abstract spread in object scope
+  }
+  randomItem {
+    id
+    ... on Article { text }          # (2) object spread in abstract scope
+    ... on Content { name }          # (4a) abstract spread in abstract scope, I == J
+    ... on HasDuration { duration }  # (4d) abstract spread in abstract scope, neither implements the other
+  }
+  repeatedStuff: randomItem {
+    id
+    id
+    url
+    otherId: id
+    ... on Article {
+      name
+      text
+      otherName: name
+    }
+    ... on Content {
+      id
+      name
+      otherName: name
+    }
+    ... on HasDuration { duration }
+  }
+  conflictingStuff: randomItem {
+    # These two have different types!  Naming gets complicated.  Note GraphQL
+    # says [1] that you can only have such naming conflicts when the fields are
+    # both on object-typed spreads (reasonable, so they can never collide) and
+    # they are of "shapes that can be merged", e.g. both nullable objects,
+    # which seems very strange to me but is the most interesting case for us
+    # anyway (since where we could have trouble is naming the result types).
+    # [1] https://spec.graphql.org/draft/#SameResponseShape()
+    # TODO(benkraft): This actually generates the wrong thing right now (the
+    # two thumbnail types get the same name, and one clobbers the other).  Fix
+    # in a follow-up commit.
+    ... on Article { thumbnail { id thumbnailUrl } }
+    ... on Video { thumbnail { id timestampSec } }
+  }
+  nestedStuff: randomItem {
+    ... on Topic {
+      children {
+        id
+        ... on Article {
+          text
+          parent {
+            ... on Content {
+              name
+              parent {
+                ... on Topic {
+                  children { id name }
+                }
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+}
diff --git a/generate/testdata/queries/Pokemon.graphql b/generate/testdata/queries/Pokemon.graphql
new file mode 100644
index 0000000..5b40414
--- /dev/null
+++ b/generate/testdata/queries/Pokemon.graphql
@@ -0,0 +1,16 @@
+query GetPokemonSiblings($input: PokemonInput!) {
+  user(query: {hasPokemon: $input}) {
+    # this will override the default mapping to internal/testutil.ID:
+    # @genqlient(bind: "string")
+    id
+    # this is normally an enum, but here we make it a (list of) string:
+    # @genqlient(bind: "[]string")
+    roles
+    name
+    # this is mapped globally to internal/testutil.Pokemon:
+    pokemon { species level }
+    # this overrides said mapping:
+    # @genqlient(bind: "-")
+    genqlientPokemon: pokemon { species level }
+  }
+}
diff --git a/generate/testdata/queries/SimpleInlineFragment.graphql b/generate/testdata/queries/SimpleInlineFragment.graphql
new file mode 100644
index 0000000..f2b75f6
--- /dev/null
+++ b/generate/testdata/queries/SimpleInlineFragment.graphql
@@ -0,0 +1,8 @@
+query SimpleInlineFragment {
+  randomItem {
+    id
+    name
+    ... on Article { text }
+    ... on Video { duration }
+  }
+}
diff --git a/generate/testdata/queries/schema.graphql b/generate/testdata/queries/schema.graphql
index dc872c8..d3c940c 100644
--- a/generate/testdata/queries/schema.graphql
+++ b/generate/testdata/queries/schema.graphql
@@ -20,6 +20,16 @@ enum Role {
   TEACHER
 }
 
+input PokemonInput {
+  species: String!
+  level: Int!
+}
+
+type Pokemon {
+  species: String!
+  level: Int!
+}
+
 """UserQueryInput is the argument to Query.users.
 
 Ideally this would support anything and everything!
@@ -33,6 +43,7 @@ input UserQueryInput {
   id: ID
   role: Role
   names: [String]
+  hasPokemon: PokemonInput
 }
 
 type AuthMethod {
@@ -53,6 +64,14 @@ type User {
   emailsWithNulls: [String]!
   emailsWithNullsOrNull: [String]
   authMethods: [AuthMethod!]!
+  pokemon: [Pokemon!]
+  greeting: Clip
+}
+
+"""An audio clip, such as of a user saying hello."""
+type Clip implements HasDuration {
+  id: ID!
+  duration: Int!
 }
 
 """Content is implemented by various types like Article, Video, and Topic."""
@@ -61,6 +80,12 @@ interface Content {
   id: ID!
   name: String!
   parent: Topic
+  url: String!
+}
+
+"""An object with a duration, like a video."""
+interface HasDuration {
+  duration: Int!
 }
 
 """LeafContent represents content items that can't have child-nodes."""
@@ -71,15 +96,29 @@ type Article implements Content {
   id: ID!
   name: String!
   parent: Topic!
+  url: String!
   text: String!
+  thumbnail: StuffThumbnail
+}
+
+type StuffThumbnail {  # for articles, but let's give the name-generator a hard time.
+  id: ID!
+  thumbnailUrl: String!
 }
 
-type Video implements Content {
+type Video implements Content & HasDuration {
   """ID is documented in the Content interface."""
   id: ID!
   name: String!
   parent: Topic!
+  url: String!
   duration: Int!
+  thumbnail: Thumbnail
+}
+
+type Thumbnail {  # for videos, but let's give the name-generator a hard time.
+  id: ID!
+  timestampSec: Int!
 }
 
 type Topic implements Content {
@@ -87,7 +126,9 @@ type Topic implements Content {
   id: ID!
   name: String!
   parent: Topic
+  url: String!
   children: [Content!]!
+  schoolGrade: String
 }
 
 """Query's description is probably ignored by almost all callers."""
diff --git a/generate/testdata/snapshots/TestGenerate-ComplexInlineFragments.graphql-ComplexInlineFragments.graphql.go b/generate/testdata/snapshots/TestGenerate-ComplexInlineFragments.graphql-ComplexInlineFragments.graphql.go
new file mode 100644
index 0000000..b223929
--- /dev/null
+++ b/generate/testdata/snapshots/TestGenerate-ComplexInlineFragments.graphql-ComplexInlineFragments.graphql.go
@@ -0,0 +1,939 @@
+package test
+
+// Code generated by github.com/Khan/genqlient, DO NOT EDIT.
+
+import (
+	"encoding/json"
+	"fmt"
+
+	"github.com/Khan/genqlient/graphql"
+	"github.com/Khan/genqlient/internal/testutil"
+)
+
+// ComplexInlineFragmentsConflictingStuffArticle includes the requested fields of the GraphQL type Article.
+type ComplexInlineFragmentsConflictingStuffArticle struct {
+	Typename  string                                          `json:"__typename"`
+	Thumbnail ComplexInlineFragmentsConflictingStuffThumbnail `json:"thumbnail"`
+}
+
+// ComplexInlineFragmentsConflictingStuffContent includes the requested fields of the GraphQL interface Content.
+//
+// ComplexInlineFragmentsConflictingStuffContent is implemented by the following types:
+// ComplexInlineFragmentsConflictingStuffArticle
+// ComplexInlineFragmentsConflictingStuffVideo
+// ComplexInlineFragmentsConflictingStuffTopic
+//
+// The GraphQL type's documentation follows.
+//
+// Content is implemented by various types like Article, Video, and Topic.
+type ComplexInlineFragmentsConflictingStuffContent interface {
+	implementsGraphQLInterfaceComplexInlineFragmentsConflictingStuffContent()
+	// GetTypename returns the receiver's concrete GraphQL type-name (see interface doc for possible values).
+	GetTypename() string
+}
+
+func (v *ComplexInlineFragmentsConflictingStuffArticle) implementsGraphQLInterfaceComplexInlineFragmentsConflictingStuffContent() {
+}
+
+// GetTypename is a part of, and documented with, the interface ComplexInlineFragmentsConflictingStuffContent.
+func (v *ComplexInlineFragmentsConflictingStuffArticle) GetTypename() string { return v.Typename }
+
+func (v *ComplexInlineFragmentsConflictingStuffVideo) implementsGraphQLInterfaceComplexInlineFragmentsConflictingStuffContent() {
+}
+
+// GetTypename is a part of, and documented with, the interface ComplexInlineFragmentsConflictingStuffContent.
+func (v *ComplexInlineFragmentsConflictingStuffVideo) GetTypename() string { return v.Typename }
+
+func (v *ComplexInlineFragmentsConflictingStuffTopic) implementsGraphQLInterfaceComplexInlineFragmentsConflictingStuffContent() {
+}
+
+// GetTypename is a part of, and documented with, the interface ComplexInlineFragmentsConflictingStuffContent.
+func (v *ComplexInlineFragmentsConflictingStuffTopic) GetTypename() string { return v.Typename }
+
+func __unmarshalComplexInlineFragmentsConflictingStuffContent(v *ComplexInlineFragmentsConflictingStuffContent, m json.RawMessage) error {
+	if string(m) == "null" {
+		return nil
+	}
+
+	var tn struct {
+		TypeName string `json:"__typename"`
+	}
+	err := json.Unmarshal(m, &tn)
+	if err != nil {
+		return err
+	}
+
+	switch tn.TypeName {
+	case "Article":
+		*v = new(ComplexInlineFragmentsConflictingStuffArticle)
+		return json.Unmarshal(m, *v)
+	case "Video":
+		*v = new(ComplexInlineFragmentsConflictingStuffVideo)
+		return json.Unmarshal(m, *v)
+	case "Topic":
+		*v = new(ComplexInlineFragmentsConflictingStuffTopic)
+		return json.Unmarshal(m, *v)
+	default:
+		return fmt.Errorf(
+			`Unexpected concrete type for ComplexInlineFragmentsConflictingStuffContent: "%v"`, tn.TypeName)
+	}
+}
+
+// ComplexInlineFragmentsConflictingStuffThumbnail includes the requested fields of the GraphQL type Thumbnail.
+type ComplexInlineFragmentsConflictingStuffThumbnail struct {
+	Id           testutil.ID `json:"id"`
+	TimestampSec int         `json:"timestampSec"`
+}
+
+// ComplexInlineFragmentsConflictingStuffTopic includes the requested fields of the GraphQL type Topic.
+type ComplexInlineFragmentsConflictingStuffTopic struct {
+	Typename string `json:"__typename"`
+}
+
+// ComplexInlineFragmentsConflictingStuffVideo includes the requested fields of the GraphQL type Video.
+type ComplexInlineFragmentsConflictingStuffVideo struct {
+	Typename  string                                          `json:"__typename"`
+	Thumbnail ComplexInlineFragmentsConflictingStuffThumbnail `json:"thumbnail"`
+}
+
+// ComplexInlineFragmentsNestedStuffArticle includes the requested fields of the GraphQL type Article.
+type ComplexInlineFragmentsNestedStuffArticle struct {
+	Typename string `json:"__typename"`
+}
+
+// ComplexInlineFragmentsNestedStuffChildrenArticle includes the requested fields of the GraphQL type Article.
+type ComplexInlineFragmentsNestedStuffChildrenArticle struct {
+	Typename string `json:"__typename"`
+	// ID is the identifier of the content.
+	Id     testutil.ID                                          `json:"id"`
+	Text   string                                               `json:"text"`
+	Parent ComplexInlineFragmentsNestedStuffChildrenParentTopic `json:"parent"`
+}
+
+// ComplexInlineFragmentsNestedStuffChildrenContent includes the requested fields of the GraphQL interface Content.
+//
+// ComplexInlineFragmentsNestedStuffChildrenContent is implemented by the following types:
+// ComplexInlineFragmentsNestedStuffChildrenArticle
+// ComplexInlineFragmentsNestedStuffChildrenVideo
+// ComplexInlineFragmentsNestedStuffChildrenTopic
+//
+// The GraphQL type's documentation follows.
+//
+// Content is implemented by various types like Article, Video, and Topic.
+type ComplexInlineFragmentsNestedStuffChildrenContent interface {
+	implementsGraphQLInterfaceComplexInlineFragmentsNestedStuffChildrenContent()
+	// GetTypename returns the receiver's concrete GraphQL type-name (see interface doc for possible values).
+	GetTypename() string
+	// GetId returns the interface-field "id" from its implementation.
+	// The GraphQL interface field's documentation follows.
+	//
+	// ID is the identifier of the content.
+	GetId() testutil.ID
+}
+
+func (v *ComplexInlineFragmentsNestedStuffChildrenArticle) implementsGraphQLInterfaceComplexInlineFragmentsNestedStuffChildrenContent() {
+}
+
+// GetTypename is a part of, and documented with, the interface ComplexInlineFragmentsNestedStuffChildrenContent.
+func (v *ComplexInlineFragmentsNestedStuffChildrenArticle) GetTypename() string { return v.Typename }
+
+// GetId is a part of, and documented with, the interface ComplexInlineFragmentsNestedStuffChildrenContent.
+func (v *ComplexInlineFragmentsNestedStuffChildrenArticle) GetId() testutil.ID { return v.Id }
+
+func (v *ComplexInlineFragmentsNestedStuffChildrenVideo) implementsGraphQLInterfaceComplexInlineFragmentsNestedStuffChildrenContent() {
+}
+
+// GetTypename is a part of, and documented with, the interface ComplexInlineFragmentsNestedStuffChildrenContent.
+func (v *ComplexInlineFragmentsNestedStuffChildrenVideo) GetTypename() string { return v.Typename }
+
+// GetId is a part of, and documented with, the interface ComplexInlineFragmentsNestedStuffChildrenContent.
+func (v *ComplexInlineFragmentsNestedStuffChildrenVideo) GetId() testutil.ID { return v.Id }
+
+func (v *ComplexInlineFragmentsNestedStuffChildrenTopic) implementsGraphQLInterfaceComplexInlineFragmentsNestedStuffChildrenContent() {
+}
+
+// GetTypename is a part of, and documented with, the interface ComplexInlineFragmentsNestedStuffChildrenContent.
+func (v *ComplexInlineFragmentsNestedStuffChildrenTopic) GetTypename() string { return v.Typename }
+
+// GetId is a part of, and documented with, the interface ComplexInlineFragmentsNestedStuffChildrenContent.
+func (v *ComplexInlineFragmentsNestedStuffChildrenTopic) GetId() testutil.ID { return v.Id }
+
+func __unmarshalComplexInlineFragmentsNestedStuffChildrenContent(v *ComplexInlineFragmentsNestedStuffChildrenContent, m json.RawMessage) error {
+	if string(m) == "null" {
+		return nil
+	}
+
+	var tn struct {
+		TypeName string `json:"__typename"`
+	}
+	err := json.Unmarshal(m, &tn)
+	if err != nil {
+		return err
+	}
+
+	switch tn.TypeName {
+	case "Article":
+		*v = new(ComplexInlineFragmentsNestedStuffChildrenArticle)
+		return json.Unmarshal(m, *v)
+	case "Video":
+		*v = new(ComplexInlineFragmentsNestedStuffChildrenVideo)
+		return json.Unmarshal(m, *v)
+	case "Topic":
+		*v = new(ComplexInlineFragmentsNestedStuffChildrenTopic)
+		return json.Unmarshal(m, *v)
+	default:
+		return fmt.Errorf(
+			`Unexpected concrete type for ComplexInlineFragmentsNestedStuffChildrenContent: "%v"`, tn.TypeName)
+	}
+}
+
+// ComplexInlineFragmentsNestedStuffChildrenParentTopic includes the requested fields of the GraphQL type Topic.
+type ComplexInlineFragmentsNestedStuffChildrenParentTopic struct {
+	Name   string                                                          `json:"name"`
+	Parent ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopic `json:"parent"`
+}
+
+// ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopic includes the requested fields of the GraphQL type Topic.
+type ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopic struct {
+	Children []ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenContent `json:"-"`
+}
+
+func (v *ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopic) UnmarshalJSON(b []byte) error {
+
+	type ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicWrapper ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopic
+
+	var firstPass struct {
+		*ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicWrapper
+		Children []json.RawMessage `json:"children"`
+	}
+	firstPass.ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicWrapper = (*ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicWrapper)(v)
+
+	err := json.Unmarshal(b, &firstPass)
+	if err != nil {
+		return err
+	}
+
+	{
+		target := &v.Children
+		raw := firstPass.Children
+		*target = make(
+			[]ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenContent,
+			len(raw))
+		for i, raw := range raw {
+			target := &(*target)[i]
+			err = __unmarshalComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenContent(
+				target, raw)
+			if err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+// ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenArticle includes the requested fields of the GraphQL type Article.
+type ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenArticle struct {
+	Typename string `json:"__typename"`
+	// ID is the identifier of the content.
+	Id   testutil.ID `json:"id"`
+	Name string      `json:"name"`
+}
+
+// ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenContent includes the requested fields of the GraphQL interface Content.
+//
+// ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenContent is implemented by the following types:
+// ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenArticle
+// ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenVideo
+// ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenTopic
+//
+// The GraphQL type's documentation follows.
+//
+// Content is implemented by various types like Article, Video, and Topic.
+type ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenContent interface {
+	implementsGraphQLInterfaceComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenContent()
+	// GetTypename returns the receiver's concrete GraphQL type-name (see interface doc for possible values).
+	GetTypename() string
+	// GetId returns the interface-field "id" from its implementation.
+	// The GraphQL interface field's documentation follows.
+	//
+	// ID is the identifier of the content.
+	GetId() testutil.ID
+	// GetName returns the interface-field "name" from its implementation.
+	GetName() string
+}
+
+func (v *ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenArticle) implementsGraphQLInterfaceComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenContent() {
+}
+
+// GetTypename is a part of, and documented with, the interface ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenContent.
+func (v *ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenArticle) GetTypename() string {
+	return v.Typename
+}
+
+// GetId is a part of, and documented with, the interface ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenContent.
+func (v *ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenArticle) GetId() testutil.ID {
+	return v.Id
+}
+
+// GetName is a part of, and documented with, the interface ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenContent.
+func (v *ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenArticle) GetName() string {
+	return v.Name
+}
+
+func (v *ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenVideo) implementsGraphQLInterfaceComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenContent() {
+}
+
+// GetTypename is a part of, and documented with, the interface ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenContent.
+func (v *ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenVideo) GetTypename() string {
+	return v.Typename
+}
+
+// GetId is a part of, and documented with, the interface ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenContent.
+func (v *ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenVideo) GetId() testutil.ID {
+	return v.Id
+}
+
+// GetName is a part of, and documented with, the interface ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenContent.
+func (v *ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenVideo) GetName() string {
+	return v.Name
+}
+
+func (v *ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenTopic) implementsGraphQLInterfaceComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenContent() {
+}
+
+// GetTypename is a part of, and documented with, the interface ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenContent.
+func (v *ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenTopic) GetTypename() string {
+	return v.Typename
+}
+
+// GetId is a part of, and documented with, the interface ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenContent.
+func (v *ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenTopic) GetId() testutil.ID {
+	return v.Id
+}
+
+// GetName is a part of, and documented with, the interface ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenContent.
+func (v *ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenTopic) GetName() string {
+	return v.Name
+}
+
+func __unmarshalComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenContent(v *ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenContent, m json.RawMessage) error {
+	if string(m) == "null" {
+		return nil
+	}
+
+	var tn struct {
+		TypeName string `json:"__typename"`
+	}
+	err := json.Unmarshal(m, &tn)
+	if err != nil {
+		return err
+	}
+
+	switch tn.TypeName {
+	case "Article":
+		*v = new(ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenArticle)
+		return json.Unmarshal(m, *v)
+	case "Video":
+		*v = new(ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenVideo)
+		return json.Unmarshal(m, *v)
+	case "Topic":
+		*v = new(ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenTopic)
+		return json.Unmarshal(m, *v)
+	default:
+		return fmt.Errorf(
+			`Unexpected concrete type for ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenContent: "%v"`, tn.TypeName)
+	}
+}
+
+// ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenTopic includes the requested fields of the GraphQL type Topic.
+type ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenTopic struct {
+	Typename string `json:"__typename"`
+	// ID is the identifier of the content.
+	Id   testutil.ID `json:"id"`
+	Name string      `json:"name"`
+}
+
+// ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenVideo includes the requested fields of the GraphQL type Video.
+type ComplexInlineFragmentsNestedStuffChildrenParentTopicParentTopicChildrenVideo struct {
+	Typename string `json:"__typename"`
+	// ID is the identifier of the content.
+	Id   testutil.ID `json:"id"`
+	Name string      `json:"name"`
+}
+
+// ComplexInlineFragmentsNestedStuffChildrenTopic includes the requested fields of the GraphQL type Topic.
+type ComplexInlineFragmentsNestedStuffChildrenTopic struct {
+	Typename string `json:"__typename"`
+	// ID is the identifier of the content.
+	Id testutil.ID `json:"id"`
+}
+
+// ComplexInlineFragmentsNestedStuffChildrenVideo includes the requested fields of the GraphQL type Video.
+type ComplexInlineFragmentsNestedStuffChildrenVideo struct {
+	Typename string `json:"__typename"`
+	// ID is the identifier of the content.
+	Id testutil.ID `json:"id"`
+}
+
+// ComplexInlineFragmentsNestedStuffContent includes the requested fields of the GraphQL interface Content.
+//
+// ComplexInlineFragmentsNestedStuffContent is implemented by the following types:
+// ComplexInlineFragmentsNestedStuffArticle
+// ComplexInlineFragmentsNestedStuffVideo
+// ComplexInlineFragmentsNestedStuffTopic
+//
+// The GraphQL type's documentation follows.
+//
+// Content is implemented by various types like Article, Video, and Topic.
+type ComplexInlineFragmentsNestedStuffContent interface {
+	implementsGraphQLInterfaceComplexInlineFragmentsNestedStuffContent()
+	// GetTypename returns the receiver's concrete GraphQL type-name (see interface doc for possible values).
+	GetTypename() string
+}
+
+func (v *ComplexInlineFragmentsNestedStuffArticle) implementsGraphQLInterfaceComplexInlineFragmentsNestedStuffContent() {
+}
+
+// GetTypename is a part of, and documented with, the interface ComplexInlineFragmentsNestedStuffContent.
+func (v *ComplexInlineFragmentsNestedStuffArticle) GetTypename() string { return v.Typename }
+
+func (v *ComplexInlineFragmentsNestedStuffVideo) implementsGraphQLInterfaceComplexInlineFragmentsNestedStuffContent() {
+}
+
+// GetTypename is a part of, and documented with, the interface ComplexInlineFragmentsNestedStuffContent.
+func (v *ComplexInlineFragmentsNestedStuffVideo) GetTypename() string { return v.Typename }
+
+func (v *ComplexInlineFragmentsNestedStuffTopic) implementsGraphQLInterfaceComplexInlineFragmentsNestedStuffContent() {
+}
+
+// GetTypename is a part of, and documented with, the interface ComplexInlineFragmentsNestedStuffContent.
+func (v *ComplexInlineFragmentsNestedStuffTopic) GetTypename() string { return v.Typename }
+
+func __unmarshalComplexInlineFragmentsNestedStuffContent(v *ComplexInlineFragmentsNestedStuffContent, m json.RawMessage) error {
+	if string(m) == "null" {
+		return nil
+	}
+
+	var tn struct {
+		TypeName string `json:"__typename"`
+	}
+	err := json.Unmarshal(m, &tn)
+	if err != nil {
+		return err
+	}
+
+	switch tn.TypeName {
+	case "Article":
+		*v = new(ComplexInlineFragmentsNestedStuffArticle)
+		return json.Unmarshal(m, *v)
+	case "Video":
+		*v = new(ComplexInlineFragmentsNestedStuffVideo)
+		return json.Unmarshal(m, *v)
+	case "Topic":
+		*v = new(ComplexInlineFragmentsNestedStuffTopic)
+		return json.Unmarshal(m, *v)
+	default:
+		return fmt.Errorf(
+			`Unexpected concrete type for ComplexInlineFragmentsNestedStuffContent: "%v"`, tn.TypeName)
+	}
+}
+
+// ComplexInlineFragmentsNestedStuffTopic includes the requested fields of the GraphQL type Topic.
+type ComplexInlineFragmentsNestedStuffTopic struct {
+	Typename string                                             `json:"__typename"`
+	Children []ComplexInlineFragmentsNestedStuffChildrenContent `json:"-"`
+}
+
+func (v *ComplexInlineFragmentsNestedStuffTopic) UnmarshalJSON(b []byte) error {
+
+	type ComplexInlineFragmentsNestedStuffTopicWrapper ComplexInlineFragmentsNestedStuffTopic
+
+	var firstPass struct {
+		*ComplexInlineFragmentsNestedStuffTopicWrapper
+		Children []json.RawMessage `json:"children"`
+	}
+	firstPass.ComplexInlineFragmentsNestedStuffTopicWrapper = (*ComplexInlineFragmentsNestedStuffTopicWrapper)(v)
+
+	err := json.Unmarshal(b, &firstPass)
+	if err != nil {
+		return err
+	}
+
+	{
+		target := &v.Children
+		raw := firstPass.Children
+		*target = make(
+			[]ComplexInlineFragmentsNestedStuffChildrenContent,
+			len(raw))
+		for i, raw := range raw {
+			target := &(*target)[i]
+			err = __unmarshalComplexInlineFragmentsNestedStuffChildrenContent(
+				target, raw)
+			if err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+// ComplexInlineFragmentsNestedStuffVideo includes the requested fields of the GraphQL type Video.
+type ComplexInlineFragmentsNestedStuffVideo struct {
+	Typename string `json:"__typename"`
+}
+
+// ComplexInlineFragmentsRandomItemArticle includes the requested fields of the GraphQL type Article.
+type ComplexInlineFragmentsRandomItemArticle struct {
+	Typename string `json:"__typename"`
+	// ID is the identifier of the content.
+	Id   testutil.ID `json:"id"`
+	Text string      `json:"text"`
+	Name string      `json:"name"`
+}
+
+// ComplexInlineFragmentsRandomItemContent includes the requested fields of the GraphQL interface Content.
+//
+// ComplexInlineFragmentsRandomItemContent is implemented by the following types:
+// ComplexInlineFragmentsRandomItemArticle
+// ComplexInlineFragmentsRandomItemVideo
+// ComplexInlineFragmentsRandomItemTopic
+//
+// The GraphQL type's documentation follows.
+//
+// Content is implemented by various types like Article, Video, and Topic.
+type ComplexInlineFragmentsRandomItemContent interface {
+	implementsGraphQLInterfaceComplexInlineFragmentsRandomItemContent()
+	// GetTypename returns the receiver's concrete GraphQL type-name (see interface doc for possible values).
+	GetTypename() string
+	// GetId returns the interface-field "id" from its implementation.
+	// The GraphQL interface field's documentation follows.
+	//
+	// ID is the identifier of the content.
+	GetId() testutil.ID
+	// GetName returns the interface-field "name" from its implementation.
+	GetName() string
+}
+
+func (v *ComplexInlineFragmentsRandomItemArticle) implementsGraphQLInterfaceComplexInlineFragmentsRandomItemContent() {
+}
+
+// GetTypename is a part of, and documented with, the interface ComplexInlineFragmentsRandomItemContent.
+func (v *ComplexInlineFragmentsRandomItemArticle) GetTypename() string { return v.Typename }
+
+// GetId is a part of, and documented with, the interface ComplexInlineFragmentsRandomItemContent.
+func (v *ComplexInlineFragmentsRandomItemArticle) GetId() testutil.ID { return v.Id }
+
+// GetName is a part of, and documented with, the interface ComplexInlineFragmentsRandomItemContent.
+func (v *ComplexInlineFragmentsRandomItemArticle) GetName() string { return v.Name }
+
+func (v *ComplexInlineFragmentsRandomItemVideo) implementsGraphQLInterfaceComplexInlineFragmentsRandomItemContent() {
+}
+
+// GetTypename is a part of, and documented with, the interface ComplexInlineFragmentsRandomItemContent.
+func (v *ComplexInlineFragmentsRandomItemVideo) GetTypename() string { return v.Typename }
+
+// GetId is a part of, and documented with, the interface ComplexInlineFragmentsRandomItemContent.
+func (v *ComplexInlineFragmentsRandomItemVideo) GetId() testutil.ID { return v.Id }
+
+// GetName is a part of, and documented with, the interface ComplexInlineFragmentsRandomItemContent.
+func (v *ComplexInlineFragmentsRandomItemVideo) GetName() string { return v.Name }
+
+func (v *ComplexInlineFragmentsRandomItemTopic) implementsGraphQLInterfaceComplexInlineFragmentsRandomItemContent() {
+}
+
+// GetTypename is a part of, and documented with, the interface ComplexInlineFragmentsRandomItemContent.
+func (v *ComplexInlineFragmentsRandomItemTopic) GetTypename() string { return v.Typename }
+
+// GetId is a part of, and documented with, the interface ComplexInlineFragmentsRandomItemContent.
+func (v *ComplexInlineFragmentsRandomItemTopic) GetId() testutil.ID { return v.Id }
+
+// GetName is a part of, and documented with, the interface ComplexInlineFragmentsRandomItemContent.
+func (v *ComplexInlineFragmentsRandomItemTopic) GetName() string { return v.Name }
+
+func __unmarshalComplexInlineFragmentsRandomItemContent(v *ComplexInlineFragmentsRandomItemContent, m json.RawMessage) error {
+	if string(m) == "null" {
+		return nil
+	}
+
+	var tn struct {
+		TypeName string `json:"__typename"`
+	}
+	err := json.Unmarshal(m, &tn)
+	if err != nil {
+		return err
+	}
+
+	switch tn.TypeName {
+	case "Article":
+		*v = new(ComplexInlineFragmentsRandomItemArticle)
+		return json.Unmarshal(m, *v)
+	case "Video":
+		*v = new(ComplexInlineFragmentsRandomItemVideo)
+		return json.Unmarshal(m, *v)
+	case "Topic":
+		*v = new(ComplexInlineFragmentsRandomItemTopic)
+		return json.Unmarshal(m, *v)
+	default:
+		return fmt.Errorf(
+			`Unexpected concrete type for ComplexInlineFragmentsRandomItemContent: "%v"`, tn.TypeName)
+	}
+}
+
+// ComplexInlineFragmentsRandomItemTopic includes the requested fields of the GraphQL type Topic.
+type ComplexInlineFragmentsRandomItemTopic struct {
+	Typename string `json:"__typename"`
+	// ID is the identifier of the content.
+	Id   testutil.ID `json:"id"`
+	Name string      `json:"name"`
+}
+
+// ComplexInlineFragmentsRandomItemVideo includes the requested fields of the GraphQL type Video.
+type ComplexInlineFragmentsRandomItemVideo struct {
+	Typename string `json:"__typename"`
+	// ID is the identifier of the content.
+	Id       testutil.ID `json:"id"`
+	Name     string      `json:"name"`
+	Duration int         `json:"duration"`
+}
+
+// ComplexInlineFragmentsRepeatedStuffArticle includes the requested fields of the GraphQL type Article.
+type ComplexInlineFragmentsRepeatedStuffArticle struct {
+	Typename string `json:"__typename"`
+	// ID is the identifier of the content.
+	Id  testutil.ID `json:"id"`
+	Url string      `json:"url"`
+	// ID is the identifier of the content.
+	OtherId   testutil.ID `json:"otherId"`
+	Name      string      `json:"name"`
+	Text      string      `json:"text"`
+	OtherName string      `json:"otherName"`
+}
+
+// ComplexInlineFragmentsRepeatedStuffContent includes the requested fields of the GraphQL interface Content.
+//
+// ComplexInlineFragmentsRepeatedStuffContent is implemented by the following types:
+// ComplexInlineFragmentsRepeatedStuffArticle
+// ComplexInlineFragmentsRepeatedStuffVideo
+// ComplexInlineFragmentsRepeatedStuffTopic
+//
+// The GraphQL type's documentation follows.
+//
+// Content is implemented by various types like Article, Video, and Topic.
+type ComplexInlineFragmentsRepeatedStuffContent interface {
+	implementsGraphQLInterfaceComplexInlineFragmentsRepeatedStuffContent()
+	// GetTypename returns the receiver's concrete GraphQL type-name (see interface doc for possible values).
+	GetTypename() string
+	// GetId returns the interface-field "id" from its implementation.
+	// The GraphQL interface field's documentation follows.
+	//
+	// ID is the identifier of the content.
+	GetId() testutil.ID
+	// GetUrl returns the interface-field "url" from its implementation.
+	GetUrl() string
+	// GetOtherId returns the interface-field "id" from its implementation.
+	// The GraphQL interface field's documentation follows.
+	//
+	// ID is the identifier of the content.
+	GetOtherId() testutil.ID
+	// GetName returns the interface-field "name" from its implementation.
+	GetName() string
+	// GetOtherName returns the interface-field "name" from its implementation.
+	GetOtherName() string
+}
+
+func (v *ComplexInlineFragmentsRepeatedStuffArticle) implementsGraphQLInterfaceComplexInlineFragmentsRepeatedStuffContent() {
+}
+
+// GetTypename is a part of, and documented with, the interface ComplexInlineFragmentsRepeatedStuffContent.
+func (v *ComplexInlineFragmentsRepeatedStuffArticle) GetTypename() string { return v.Typename }
+
+// GetId is a part of, and documented with, the interface ComplexInlineFragmentsRepeatedStuffContent.
+func (v *ComplexInlineFragmentsRepeatedStuffArticle) GetId() testutil.ID { return v.Id }
+
+// GetUrl is a part of, and documented with, the interface ComplexInlineFragmentsRepeatedStuffContent.
+func (v *ComplexInlineFragmentsRepeatedStuffArticle) GetUrl() string { return v.Url }
+
+// GetOtherId is a part of, and documented with, the interface ComplexInlineFragmentsRepeatedStuffContent.
+func (v *ComplexInlineFragmentsRepeatedStuffArticle) GetOtherId() testutil.ID { return v.OtherId }
+
+// GetName is a part of, and documented with, the interface ComplexInlineFragmentsRepeatedStuffContent.
+func (v *ComplexInlineFragmentsRepeatedStuffArticle) GetName() string { return v.Name }
+
+// GetOtherName is a part of, and documented with, the interface ComplexInlineFragmentsRepeatedStuffContent.
+func (v *ComplexInlineFragmentsRepeatedStuffArticle) GetOtherName() string { return v.OtherName }
+
+func (v *ComplexInlineFragmentsRepeatedStuffVideo) implementsGraphQLInterfaceComplexInlineFragmentsRepeatedStuffContent() {
+}
+
+// GetTypename is a part of, and documented with, the interface ComplexInlineFragmentsRepeatedStuffContent.
+func (v *ComplexInlineFragmentsRepeatedStuffVideo) GetTypename() string { return v.Typename }
+
+// GetId is a part of, and documented with, the interface ComplexInlineFragmentsRepeatedStuffContent.
+func (v *ComplexInlineFragmentsRepeatedStuffVideo) GetId() testutil.ID { return v.Id }
+
+// GetUrl is a part of, and documented with, the interface ComplexInlineFragmentsRepeatedStuffContent.
+func (v *ComplexInlineFragmentsRepeatedStuffVideo) GetUrl() string { return v.Url }
+
+// GetOtherId is a part of, and documented with, the interface ComplexInlineFragmentsRepeatedStuffContent.
+func (v *ComplexInlineFragmentsRepeatedStuffVideo) GetOtherId() testutil.ID { return v.OtherId }
+
+// GetName is a part of, and documented with, the interface ComplexInlineFragmentsRepeatedStuffContent.
+func (v *ComplexInlineFragmentsRepeatedStuffVideo) GetName() string { return v.Name }
+
+// GetOtherName is a part of, and documented with, the interface ComplexInlineFragmentsRepeatedStuffContent.
+func (v *ComplexInlineFragmentsRepeatedStuffVideo) GetOtherName() string { return v.OtherName }
+
+func (v *ComplexInlineFragmentsRepeatedStuffTopic) implementsGraphQLInterfaceComplexInlineFragmentsRepeatedStuffContent() {
+}
+
+// GetTypename is a part of, and documented with, the interface ComplexInlineFragmentsRepeatedStuffContent.
+func (v *ComplexInlineFragmentsRepeatedStuffTopic) GetTypename() string { return v.Typename }
+
+// GetId is a part of, and documented with, the interface ComplexInlineFragmentsRepeatedStuffContent.
+func (v *ComplexInlineFragmentsRepeatedStuffTopic) GetId() testutil.ID { return v.Id }
+
+// GetUrl is a part of, and documented with, the interface ComplexInlineFragmentsRepeatedStuffContent.
+func (v *ComplexInlineFragmentsRepeatedStuffTopic) GetUrl() string { return v.Url }
+
+// GetOtherId is a part of, and documented with, the interface ComplexInlineFragmentsRepeatedStuffContent.
+func (v *ComplexInlineFragmentsRepeatedStuffTopic) GetOtherId() testutil.ID { return v.OtherId }
+
+// GetName is a part of, and documented with, the interface ComplexInlineFragmentsRepeatedStuffContent.
+func (v *ComplexInlineFragmentsRepeatedStuffTopic) GetName() string { return v.Name }
+
+// GetOtherName is a part of, and documented with, the interface ComplexInlineFragmentsRepeatedStuffContent.
+func (v *ComplexInlineFragmentsRepeatedStuffTopic) GetOtherName() string { return v.OtherName }
+
+func __unmarshalComplexInlineFragmentsRepeatedStuffContent(v *ComplexInlineFragmentsRepeatedStuffContent, m json.RawMessage) error {
+	if string(m) == "null" {
+		return nil
+	}
+
+	var tn struct {
+		TypeName string `json:"__typename"`
+	}
+	err := json.Unmarshal(m, &tn)
+	if err != nil {
+		return err
+	}
+
+	switch tn.TypeName {
+	case "Article":
+		*v = new(ComplexInlineFragmentsRepeatedStuffArticle)
+		return json.Unmarshal(m, *v)
+	case "Video":
+		*v = new(ComplexInlineFragmentsRepeatedStuffVideo)
+		return json.Unmarshal(m, *v)
+	case "Topic":
+		*v = new(ComplexInlineFragmentsRepeatedStuffTopic)
+		return json.Unmarshal(m, *v)
+	default:
+		return fmt.Errorf(
+			`Unexpected concrete type for ComplexInlineFragmentsRepeatedStuffContent: "%v"`, tn.TypeName)
+	}
+}
+
+// ComplexInlineFragmentsRepeatedStuffTopic includes the requested fields of the GraphQL type Topic.
+type ComplexInlineFragmentsRepeatedStuffTopic struct {
+	Typename string `json:"__typename"`
+	// ID is the identifier of the content.
+	Id  testutil.ID `json:"id"`
+	Url string      `json:"url"`
+	// ID is the identifier of the content.
+	OtherId   testutil.ID `json:"otherId"`
+	Name      string      `json:"name"`
+	OtherName string      `json:"otherName"`
+}
+
+// ComplexInlineFragmentsRepeatedStuffVideo includes the requested fields of the GraphQL type Video.
+type ComplexInlineFragmentsRepeatedStuffVideo struct {
+	Typename string `json:"__typename"`
+	// ID is the identifier of the content.
+	Id  testutil.ID `json:"id"`
+	Url string      `json:"url"`
+	// ID is the identifier of the content.
+	OtherId   testutil.ID `json:"otherId"`
+	Name      string      `json:"name"`
+	OtherName string      `json:"otherName"`
+	Duration  int         `json:"duration"`
+}
+
+// ComplexInlineFragmentsResponse is returned by ComplexInlineFragments on success.
+type ComplexInlineFragmentsResponse struct {
+	Root             ComplexInlineFragmentsRootTopic               `json:"root"`
+	RandomItem       ComplexInlineFragmentsRandomItemContent       `json:"-"`
+	RepeatedStuff    ComplexInlineFragmentsRepeatedStuffContent    `json:"-"`
+	ConflictingStuff ComplexInlineFragmentsConflictingStuffContent `json:"-"`
+	NestedStuff      ComplexInlineFragmentsNestedStuffContent      `json:"-"`
+}
+
+func (v *ComplexInlineFragmentsResponse) UnmarshalJSON(b []byte) error {
+
+	type ComplexInlineFragmentsResponseWrapper ComplexInlineFragmentsResponse
+
+	var firstPass struct {
+		*ComplexInlineFragmentsResponseWrapper
+		RandomItem       json.RawMessage `json:"randomItem"`
+		RepeatedStuff    json.RawMessage `json:"repeatedStuff"`
+		ConflictingStuff json.RawMessage `json:"conflictingStuff"`
+		NestedStuff      json.RawMessage `json:"nestedStuff"`
+	}
+	firstPass.ComplexInlineFragmentsResponseWrapper = (*ComplexInlineFragmentsResponseWrapper)(v)
+
+	err := json.Unmarshal(b, &firstPass)
+	if err != nil {
+		return err
+	}
+
+	{
+		target := &v.RandomItem
+		raw := firstPass.RandomItem
+		err = __unmarshalComplexInlineFragmentsRandomItemContent(
+			target, raw)
+		if err != nil {
+			return err
+		}
+	}
+	{
+		target := &v.RepeatedStuff
+		raw := firstPass.RepeatedStuff
+		err = __unmarshalComplexInlineFragmentsRepeatedStuffContent(
+			target, raw)
+		if err != nil {
+			return err
+		}
+	}
+	{
+		target := &v.ConflictingStuff
+		raw := firstPass.ConflictingStuff
+		err = __unmarshalComplexInlineFragmentsConflictingStuffContent(
+			target, raw)
+		if err != nil {
+			return err
+		}
+	}
+	{
+		target := &v.NestedStuff
+		raw := firstPass.NestedStuff
+		err = __unmarshalComplexInlineFragmentsNestedStuffContent(
+			target, raw)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// ComplexInlineFragmentsRootTopic includes the requested fields of the GraphQL type Topic.
+type ComplexInlineFragmentsRootTopic struct {
+	// ID is documented in the Content interface.
+	Id          testutil.ID `json:"id"`
+	SchoolGrade string      `json:"schoolGrade"`
+	Name        string      `json:"name"`
+}
+
+// We test all the spread cases from DESIGN.md, see there for more context on
+// each, as well as various other nonsense.  But for abstract-in-abstract
+// spreads, we can't test cases (4b) and (4c), where I implements J or vice
+// versa, because gqlparser doesn't support interfaces that implement other
+// interfaces yet.
+func ComplexInlineFragments(
+	client graphql.Client,
+) (*ComplexInlineFragmentsResponse, error) {
+	var retval ComplexInlineFragmentsResponse
+	err := client.MakeRequest(
+		nil,
+		"ComplexInlineFragments",
+		`
+query ComplexInlineFragments {
+	root {
+		id
+		... on Topic {
+			schoolGrade
+		}
+		... on Content {
+			name
+		}
+	}
+	randomItem {
+		__typename
+		id
+		... on Article {
+			text
+		}
+		... on Content {
+			name
+		}
+		... on HasDuration {
+			duration
+		}
+	}
+	repeatedStuff: randomItem {
+		__typename
+		id
+		id
+		url
+		otherId: id
+		... on Article {
+			name
+			text
+			otherName: name
+		}
+		... on Content {
+			id
+			name
+			otherName: name
+		}
+		... on HasDuration {
+			duration
+		}
+	}
+	conflictingStuff: randomItem {
+		__typename
+		... on Article {
+			thumbnail {
+				id
+				thumbnailUrl
+			}
+		}
+		... on Video {
+			thumbnail {
+				id
+				timestampSec
+			}
+		}
+	}
+	nestedStuff: randomItem {
+		__typename
+		... on Topic {
+			children {
+				__typename
+				id
+				... on Article {
+					text
+					parent {
+						... on Content {
+							name
+							parent {
+								... on Topic {
+									children {
+										__typename
+										id
+										name
+									}
+								}
+							}
+						}
+					}
+				}
+			}
+		}
+	}
+}
+`,
+		&retval,
+		nil,
+	)
+	return &retval, err
+}
+
diff --git a/generate/testdata/snapshots/TestGenerate-ComplexInlineFragments.graphql-ComplexInlineFragments.graphql.json b/generate/testdata/snapshots/TestGenerate-ComplexInlineFragments.graphql-ComplexInlineFragments.graphql.json
new file mode 100644
index 0000000..357c889
--- /dev/null
+++ b/generate/testdata/snapshots/TestGenerate-ComplexInlineFragments.graphql-ComplexInlineFragments.graphql.json
@@ -0,0 +1,9 @@
+{
+  "operations": [
+    {
+      "operationName": "ComplexInlineFragments",
+      "query": "\nquery ComplexInlineFragments {\n\troot {\n\t\tid\n\t\t... on Topic {\n\t\t\tschoolGrade\n\t\t}\n\t\t... on Content {\n\t\t\tname\n\t\t}\n\t}\n\trandomItem {\n\t\t__typename\n\t\tid\n\t\t... on Article {\n\t\t\ttext\n\t\t}\n\t\t... on Content {\n\t\t\tname\n\t\t}\n\t\t... on HasDuration {\n\t\t\tduration\n\t\t}\n\t}\n\trepeatedStuff: randomItem {\n\t\t__typename\n\t\tid\n\t\tid\n\t\turl\n\t\totherId: id\n\t\t... on Article {\n\t\t\tname\n\t\t\ttext\n\t\t\totherName: name\n\t\t}\n\t\t... on Content {\n\t\t\tid\n\t\t\tname\n\t\t\totherName: name\n\t\t}\n\t\t... on HasDuration {\n\t\t\tduration\n\t\t}\n\t}\n\tconflictingStuff: randomItem {\n\t\t__typename\n\t\t... on Article {\n\t\t\tthumbnail {\n\t\t\t\tid\n\t\t\t\tthumbnailUrl\n\t\t\t}\n\t\t}\n\t\t... on Video {\n\t\t\tthumbnail {\n\t\t\t\tid\n\t\t\t\ttimestampSec\n\t\t\t}\n\t\t}\n\t}\n\tnestedStuff: randomItem {\n\t\t__typename\n\t\t... on Topic {\n\t\t\tchildren {\n\t\t\t\t__typename\n\t\t\t\tid\n\t\t\t\t... on Article {\n\t\t\t\t\ttext\n\t\t\t\t\tparent {\n\t\t\t\t\t\t... on Content {\n\t\t\t\t\t\t\tname\n\t\t\t\t\t\t\tparent {\n\t\t\t\t\t\t\t\t... on Topic {\n\t\t\t\t\t\t\t\t\tchildren {\n\t\t\t\t\t\t\t\t\t\t__typename\n\t\t\t\t\t\t\t\t\t\tid\n\t\t\t\t\t\t\t\t\t\tname\n\t\t\t\t\t\t\t\t\t}\n\t\t\t\t\t\t\t\t}\n\t\t\t\t\t\t\t}\n\t\t\t\t\t\t}\n\t\t\t\t\t}\n\t\t\t\t}\n\t\t\t}\n\t\t}\n\t}\n}\n",
+      "sourceLocation": "testdata/queries/ComplexInlineFragments.graphql"
+    }
+  ]
+}
diff --git a/generate/testdata/snapshots/TestGenerate-InputObject.graphql-InputObject.graphql.go b/generate/testdata/snapshots/TestGenerate-InputObject.graphql-InputObject.graphql.go
index 2f844be..288650c 100644
--- a/generate/testdata/snapshots/TestGenerate-InputObject.graphql-InputObject.graphql.go
+++ b/generate/testdata/snapshots/TestGenerate-InputObject.graphql-InputObject.graphql.go
@@ -50,9 +50,10 @@ type UserQueryInput struct {
 	Email string `json:"email"`
 	Name  string `json:"name"`
 	// id looks the user up by ID.  It's a great way to look up users.
-	Id    testutil.ID `json:"id"`
-	Role  Role        `json:"role"`
-	Names []string    `json:"names"`
+	Id         testutil.ID      `json:"id"`
+	Role       Role             `json:"role"`
+	Names      []string         `json:"names"`
+	HasPokemon testutil.Pokemon `json:"hasPokemon"`
 }
 
 func InputObjectQuery(
diff --git a/generate/testdata/snapshots/TestGenerate-InterfaceListField.graphql-InterfaceListField.graphql.go b/generate/testdata/snapshots/TestGenerate-InterfaceListField.graphql-InterfaceListField.graphql.go
index df0cea5..c5619bd 100644
--- a/generate/testdata/snapshots/TestGenerate-InterfaceListField.graphql-InterfaceListField.graphql.go
+++ b/generate/testdata/snapshots/TestGenerate-InterfaceListField.graphql-InterfaceListField.graphql.go
@@ -50,7 +50,8 @@ func (v *InterfaceListFieldRootTopic) UnmarshalJSON(b []byte) error {
 			err = __unmarshalInterfaceListFieldRootTopicChildrenContent(
 				target, raw)
 			if err != nil {
-				return err
+				return fmt.Errorf(
+					"Unable to unmarshal InterfaceListFieldRootTopic.Children: %w", err)
 			}
 		}
 	}
@@ -147,6 +148,9 @@ func __unmarshalInterfaceListFieldRootTopicChildrenContent(v *InterfaceListField
 	case "Topic":
 		*v = new(InterfaceListFieldRootTopicChildrenTopic)
 		return json.Unmarshal(m, *v)
+	case "":
+		return fmt.Errorf(
+			"Response was missing Content.__typename")
 	default:
 		return fmt.Errorf(
 			`Unexpected concrete type for InterfaceListFieldRootTopicChildrenContent: "%v"`, tn.TypeName)
@@ -203,7 +207,8 @@ func (v *InterfaceListFieldWithPointerTopic) UnmarshalJSON(b []byte) error {
 			err = __unmarshalInterfaceListFieldWithPointerTopicChildrenContent(
 				target, raw)
 			if err != nil {
-				return err
+				return fmt.Errorf(
+					"Unable to unmarshal InterfaceListFieldWithPointerTopic.Children: %w", err)
 			}
 		}
 	}
@@ -300,6 +305,9 @@ func __unmarshalInterfaceListFieldWithPointerTopicChildrenContent(v *InterfaceLi
 	case "Topic":
 		*v = new(InterfaceListFieldWithPointerTopicChildrenTopic)
 		return json.Unmarshal(m, *v)
+	case "":
+		return fmt.Errorf(
+			"Response was missing Content.__typename")
 	default:
 		return fmt.Errorf(
 			`Unexpected concrete type for InterfaceListFieldWithPointerTopicChildrenContent: "%v"`, tn.TypeName)
diff --git a/generate/testdata/snapshots/TestGenerate-InterfaceListOfListsOfListsField.graphql-InterfaceListOfListsOfListsField.graphql.go b/generate/testdata/snapshots/TestGenerate-InterfaceListOfListsOfListsField.graphql-InterfaceListOfListsOfListsField.graphql.go
index f91a299..ffcc237 100644
--- a/generate/testdata/snapshots/TestGenerate-InterfaceListOfListsOfListsField.graphql-InterfaceListOfListsOfListsField.graphql.go
+++ b/generate/testdata/snapshots/TestGenerate-InterfaceListOfListsOfListsField.graphql-InterfaceListOfListsOfListsField.graphql.go
@@ -110,6 +110,9 @@ func __unmarshalInterfaceListOfListOfListsFieldListOfListsOfListsOfContent(v *In
 	case "Topic":
 		*v = new(InterfaceListOfListOfListsFieldListOfListsOfListsOfContentTopic)
 		return json.Unmarshal(m, *v)
+	case "":
+		return fmt.Errorf(
+			"Response was missing Content.__typename")
 	default:
 		return fmt.Errorf(
 			`Unexpected concrete type for InterfaceListOfListOfListsFieldListOfListsOfListsOfContent: "%v"`, tn.TypeName)
@@ -183,7 +186,8 @@ func (v *InterfaceListOfListOfListsFieldResponse) UnmarshalJSON(b []byte) error
 					err = __unmarshalInterfaceListOfListOfListsFieldListOfListsOfListsOfContent(
 						target, raw)
 					if err != nil {
-						return err
+						return fmt.Errorf(
+							"Unable to unmarshal InterfaceListOfListOfListsFieldResponse.ListOfListsOfListsOfContent: %w", err)
 					}
 				}
 			}
@@ -211,7 +215,8 @@ func (v *InterfaceListOfListOfListsFieldResponse) UnmarshalJSON(b []byte) error
 					err = __unmarshalInterfaceListOfListOfListsFieldWithPointerContent(
 						*target, raw)
 					if err != nil {
-						return err
+						return fmt.Errorf(
+							"Unable to unmarshal InterfaceListOfListOfListsFieldResponse.WithPointer: %w", err)
 					}
 				}
 			}
@@ -310,6 +315,9 @@ func __unmarshalInterfaceListOfListOfListsFieldWithPointerContent(v *InterfaceLi
 	case "Topic":
 		*v = new(InterfaceListOfListOfListsFieldWithPointerTopic)
 		return json.Unmarshal(m, *v)
+	case "":
+		return fmt.Errorf(
+			"Response was missing Content.__typename")
 	default:
 		return fmt.Errorf(
 			`Unexpected concrete type for InterfaceListOfListOfListsFieldWithPointerContent: "%v"`, tn.TypeName)
diff --git a/generate/testdata/snapshots/TestGenerate-InterfaceNesting.graphql-InterfaceNesting.graphql.go b/generate/testdata/snapshots/TestGenerate-InterfaceNesting.graphql-InterfaceNesting.graphql.go
index 336bf1d..1cb1d33 100644
--- a/generate/testdata/snapshots/TestGenerate-InterfaceNesting.graphql-InterfaceNesting.graphql.go
+++ b/generate/testdata/snapshots/TestGenerate-InterfaceNesting.graphql-InterfaceNesting.graphql.go
@@ -48,7 +48,8 @@ func (v *InterfaceNestingRootTopic) UnmarshalJSON(b []byte) error {
 			err = __unmarshalInterfaceNestingRootTopicChildrenContent(
 				target, raw)
 			if err != nil {
-				return err
+				return fmt.Errorf(
+					"Unable to unmarshal InterfaceNestingRootTopic.Children: %w", err)
 			}
 		}
 	}
@@ -151,6 +152,9 @@ func __unmarshalInterfaceNestingRootTopicChildrenContent(v *InterfaceNestingRoot
 	case "Topic":
 		*v = new(InterfaceNestingRootTopicChildrenTopic)
 		return json.Unmarshal(m, *v)
+	case "":
+		return fmt.Errorf(
+			"Response was missing Content.__typename")
 	default:
 		return fmt.Errorf(
 			`Unexpected concrete type for InterfaceNestingRootTopicChildrenContent: "%v"`, tn.TypeName)
@@ -190,7 +194,8 @@ func (v *InterfaceNestingRootTopicChildrenParentTopic) UnmarshalJSON(b []byte) e
 			err = __unmarshalInterfaceNestingRootTopicChildrenParentTopicChildrenContent(
 				target, raw)
 			if err != nil {
-				return err
+				return fmt.Errorf(
+					"Unable to unmarshal InterfaceNestingRootTopicChildrenParentTopic.Children: %w", err)
 			}
 		}
 	}
@@ -283,6 +288,9 @@ func __unmarshalInterfaceNestingRootTopicChildrenParentTopicChildrenContent(v *I
 	case "Topic":
 		*v = new(InterfaceNestingRootTopicChildrenParentTopicChildrenTopic)
 		return json.Unmarshal(m, *v)
+	case "":
+		return fmt.Errorf(
+			"Response was missing Content.__typename")
 	default:
 		return fmt.Errorf(
 			`Unexpected concrete type for InterfaceNestingRootTopicChildrenParentTopicChildrenContent: "%v"`, tn.TypeName)
diff --git a/generate/testdata/snapshots/TestGenerate-InterfaceNoFragments.graphql-InterfaceNoFragments.graphql.go b/generate/testdata/snapshots/TestGenerate-InterfaceNoFragments.graphql-InterfaceNoFragments.graphql.go
index a581c53..10b0aa1 100644
--- a/generate/testdata/snapshots/TestGenerate-InterfaceNoFragments.graphql-InterfaceNoFragments.graphql.go
+++ b/generate/testdata/snapshots/TestGenerate-InterfaceNoFragments.graphql-InterfaceNoFragments.graphql.go
@@ -100,6 +100,9 @@ func __unmarshalInterfaceNoFragmentsQueryRandomItemContent(v *InterfaceNoFragmen
 	case "Topic":
 		*v = new(InterfaceNoFragmentsQueryRandomItemTopic)
 		return json.Unmarshal(m, *v)
+	case "":
+		return fmt.Errorf(
+			"Response was missing Content.__typename")
 	default:
 		return fmt.Errorf(
 			`Unexpected concrete type for InterfaceNoFragmentsQueryRandomItemContent: "%v"`, tn.TypeName)
@@ -218,6 +221,9 @@ func __unmarshalInterfaceNoFragmentsQueryRandomItemWithTypeNameContent(v *Interf
 	case "Topic":
 		*v = new(InterfaceNoFragmentsQueryRandomItemWithTypeNameTopic)
 		return json.Unmarshal(m, *v)
+	case "":
+		return fmt.Errorf(
+			"Response was missing Content.__typename")
 	default:
 		return fmt.Errorf(
 			`Unexpected concrete type for InterfaceNoFragmentsQueryRandomItemWithTypeNameContent: "%v"`, tn.TypeName)
@@ -271,7 +277,8 @@ func (v *InterfaceNoFragmentsQueryResponse) UnmarshalJSON(b []byte) error {
 		err = __unmarshalInterfaceNoFragmentsQueryRandomItemContent(
 			target, raw)
 		if err != nil {
-			return err
+			return fmt.Errorf(
+				"Unable to unmarshal InterfaceNoFragmentsQueryResponse.RandomItem: %w", err)
 		}
 	}
 	{
@@ -280,7 +287,8 @@ func (v *InterfaceNoFragmentsQueryResponse) UnmarshalJSON(b []byte) error {
 		err = __unmarshalInterfaceNoFragmentsQueryRandomItemWithTypeNameContent(
 			target, raw)
 		if err != nil {
-			return err
+			return fmt.Errorf(
+				"Unable to unmarshal InterfaceNoFragmentsQueryResponse.RandomItemWithTypeName: %w", err)
 		}
 	}
 	{
@@ -290,7 +298,8 @@ func (v *InterfaceNoFragmentsQueryResponse) UnmarshalJSON(b []byte) error {
 		err = __unmarshalInterfaceNoFragmentsQueryWithPointerContent(
 			*target, raw)
 		if err != nil {
-			return err
+			return fmt.Errorf(
+				"Unable to unmarshal InterfaceNoFragmentsQueryResponse.WithPointer: %w", err)
 		}
 	}
 	return nil
@@ -393,6 +402,9 @@ func __unmarshalInterfaceNoFragmentsQueryWithPointerContent(v *InterfaceNoFragme
 	case "Topic":
 		*v = new(InterfaceNoFragmentsQueryWithPointerTopic)
 		return json.Unmarshal(m, *v)
+	case "":
+		return fmt.Errorf(
+			"Response was missing Content.__typename")
 	default:
 		return fmt.Errorf(
 			`Unexpected concrete type for InterfaceNoFragmentsQueryWithPointerContent: "%v"`, tn.TypeName)
diff --git a/generate/testdata/snapshots/TestGenerate-Omitempty.graphql-Omitempty.graphql.go b/generate/testdata/snapshots/TestGenerate-Omitempty.graphql-Omitempty.graphql.go
index 77c2d58..4d750cd 100644
--- a/generate/testdata/snapshots/TestGenerate-Omitempty.graphql-Omitempty.graphql.go
+++ b/generate/testdata/snapshots/TestGenerate-Omitempty.graphql-Omitempty.graphql.go
@@ -66,9 +66,10 @@ type UserQueryInput struct {
 	Email string `json:"email"`
 	Name  string `json:"name"`
 	// id looks the user up by ID.  It's a great way to look up users.
-	Id    testutil.ID `json:"id"`
-	Role  Role        `json:"role"`
-	Names []string    `json:"names"`
+	Id         testutil.ID      `json:"id"`
+	Role       Role             `json:"role"`
+	Names      []string         `json:"names"`
+	HasPokemon testutil.Pokemon `json:"hasPokemon"`
 }
 
 func OmitEmptyQuery(
diff --git a/generate/testdata/snapshots/TestGenerate-Pointers.graphql-Pointers.graphql.go b/generate/testdata/snapshots/TestGenerate-Pointers.graphql-Pointers.graphql.go
index 8862ff9..0a17884 100644
--- a/generate/testdata/snapshots/TestGenerate-Pointers.graphql-Pointers.graphql.go
+++ b/generate/testdata/snapshots/TestGenerate-Pointers.graphql-Pointers.graphql.go
@@ -73,9 +73,10 @@ type UserQueryInput struct {
 	Email *string `json:"email"`
 	Name  *string `json:"name"`
 	// id looks the user up by ID.  It's a great way to look up users.
-	Id    *testutil.ID `json:"id"`
-	Role  *Role        `json:"role"`
-	Names []*string    `json:"names"`
+	Id         *testutil.ID      `json:"id"`
+	Role       *Role             `json:"role"`
+	Names      []*string         `json:"names"`
+	HasPokemon *testutil.Pokemon `json:"hasPokemon"`
 }
 
 func PointersQuery(
diff --git a/generate/testdata/snapshots/TestGenerate-PointersInline.graphql-PointersInline.graphql.go b/generate/testdata/snapshots/TestGenerate-PointersInline.graphql-PointersInline.graphql.go
index 8ab0598..d3ada1e 100644
--- a/generate/testdata/snapshots/TestGenerate-PointersInline.graphql-PointersInline.graphql.go
+++ b/generate/testdata/snapshots/TestGenerate-PointersInline.graphql-PointersInline.graphql.go
@@ -73,9 +73,10 @@ type UserQueryInput struct {
 	Email string `json:"email"`
 	Name  string `json:"name"`
 	// id looks the user up by ID.  It's a great way to look up users.
-	Id    testutil.ID `json:"id"`
-	Role  Role        `json:"role"`
-	Names []string    `json:"names"`
+	Id         testutil.ID      `json:"id"`
+	Role       Role             `json:"role"`
+	Names      []string         `json:"names"`
+	HasPokemon testutil.Pokemon `json:"hasPokemon"`
 }
 
 func PointersQuery(
diff --git a/generate/testdata/snapshots/TestGenerate-Pokemon.graphql-Pokemon.graphql.go b/generate/testdata/snapshots/TestGenerate-Pokemon.graphql-Pokemon.graphql.go
new file mode 100644
index 0000000..4a4796b
--- /dev/null
+++ b/generate/testdata/snapshots/TestGenerate-Pokemon.graphql-Pokemon.graphql.go
@@ -0,0 +1,74 @@
+package test
+
+// Code generated by github.com/Khan/genqlient, DO NOT EDIT.
+
+import (
+	"github.com/Khan/genqlient/graphql"
+	"github.com/Khan/genqlient/internal/testutil"
+)
+
+// GetPokemonSiblingsResponse is returned by GetPokemonSiblings on success.
+type GetPokemonSiblingsResponse struct {
+	// user looks up a user by some stuff.
+	//
+	// See UserQueryInput for what stuff is supported.
+	// If query is null, returns the current user.
+	User GetPokemonSiblingsUser `json:"user"`
+}
+
+// GetPokemonSiblingsUser includes the requested fields of the GraphQL type User.
+// The GraphQL type's documentation follows.
+//
+// A User is a user!
+type GetPokemonSiblingsUser struct {
+	// id is the user's ID.
+	//
+	// It is stable, unique, and opaque, like all good IDs.
+	Id               string                                   `json:"id"`
+	Roles            []string                                 `json:"roles"`
+	Name             string                                   `json:"name"`
+	Pokemon          []testutil.Pokemon                       `json:"pokemon"`
+	GenqlientPokemon []GetPokemonSiblingsUserGenqlientPokemon `json:"genqlientPokemon"`
+}
+
+// GetPokemonSiblingsUserGenqlientPokemon includes the requested fields of the GraphQL type Pokemon.
+type GetPokemonSiblingsUserGenqlientPokemon struct {
+	Species string `json:"species"`
+	Level   int    `json:"level"`
+}
+
+func GetPokemonSiblings(
+	client graphql.Client,
+	input testutil.Pokemon,
+) (*GetPokemonSiblingsResponse, error) {
+	variables := map[string]interface{}{
+		"input": input,
+	}
+
+	var retval GetPokemonSiblingsResponse
+	err := client.MakeRequest(
+		nil,
+		"GetPokemonSiblings",
+		`
+query GetPokemonSiblings ($input: PokemonInput!) {
+	user(query: {hasPokemon:$input}) {
+		id
+		roles
+		name
+		pokemon {
+			species
+			level
+		}
+		genqlientPokemon: pokemon {
+			species
+			level
+		}
+	}
+}
+`,
+		&retval,
+		variables,
+	)
+	return &retval, err
+}
+
diff --git a/generate/testdata/snapshots/TestGenerate-Pokemon.graphql-Pokemon.graphql.json b/generate/testdata/snapshots/TestGenerate-Pokemon.graphql-Pokemon.graphql.json
new file mode 100644
index 0000000..046d226
--- /dev/null
+++ b/generate/testdata/snapshots/TestGenerate-Pokemon.graphql-Pokemon.graphql.json
@@ -0,0 +1,9 @@
+{
+  "operations": [
+    {
+      "operationName": "GetPokemonSiblings",
+      "query": "\nquery GetPokemonSiblings ($input: PokemonInput!) {\n\tuser(query: {hasPokemon:$input}) {\n\t\tid\n\t\troles\n\t\tname\n\t\tpokemon {\n\t\t\tspecies\n\t\t\tlevel\n\t\t}\n\t\tgenqlientPokemon: pokemon {\n\t\t\tspecies\n\t\t\tlevel\n\t\t}\n\t}\n}\n",
+      "sourceLocation": "testdata/queries/Pokemon.graphql"
+    }
+  ]
+}
diff --git a/generate/testdata/snapshots/TestGenerate-SimpleInlineFragment.graphql-SimpleInlineFragment.graphql.go b/generate/testdata/snapshots/TestGenerate-SimpleInlineFragment.graphql-SimpleInlineFragment.graphql.go
new file mode 100644
index 0000000..f3e2702
--- /dev/null
+++ b/generate/testdata/snapshots/TestGenerate-SimpleInlineFragment.graphql-SimpleInlineFragment.graphql.go
@@ -0,0 +1,186 @@
+package test
+
+// Code generated by github.com/Khan/genqlient, DO NOT EDIT.
+
+import (
+	"encoding/json"
+	"fmt"
+
+	"github.com/Khan/genqlient/graphql"
+	"github.com/Khan/genqlient/internal/testutil"
+)
+
+// SimpleInlineFragmentRandomItemArticle includes the requested fields of the GraphQL type Article.
+type SimpleInlineFragmentRandomItemArticle struct {
+	Typename string `json:"__typename"`
+	// ID is the identifier of the content.
+	Id   testutil.ID `json:"id"`
+	Name string      `json:"name"`
+	Text string      `json:"text"`
+}
+
+// SimpleInlineFragmentRandomItemContent includes the requested fields of the GraphQL interface Content.
+//
+// SimpleInlineFragmentRandomItemContent is implemented by the following types:
+// SimpleInlineFragmentRandomItemArticle
+// SimpleInlineFragmentRandomItemVideo
+// SimpleInlineFragmentRandomItemTopic
+//
+// The GraphQL type's documentation follows.
+//
+// Content is implemented by various types like Article, Video, and Topic.
+type SimpleInlineFragmentRandomItemContent interface {
+	implementsGraphQLInterfaceSimpleInlineFragmentRandomItemContent()
+	// GetTypename returns the receiver's concrete GraphQL type-name (see interface doc for possible values).
+	GetTypename() string
+	// GetId returns the interface-field "id" from its implementation.
+	// The GraphQL interface field's documentation follows.
+	//
+	// ID is the identifier of the content.
+	GetId() testutil.ID
+	// GetName returns the interface-field "name" from its implementation.
+	GetName() string
+}
+
+func (v *SimpleInlineFragmentRandomItemArticle) implementsGraphQLInterfaceSimpleInlineFragmentRandomItemContent() {
+}
+
+// GetTypename is a part of, and documented with, the interface SimpleInlineFragmentRandomItemContent.
+func (v *SimpleInlineFragmentRandomItemArticle) GetTypename() string { return v.Typename }
+
+// GetId is a part of, and documented with, the interface SimpleInlineFragmentRandomItemContent.
+func (v *SimpleInlineFragmentRandomItemArticle) GetId() testutil.ID { return v.Id }
+
+// GetName is a part of, and documented with, the interface SimpleInlineFragmentRandomItemContent.
+func (v *SimpleInlineFragmentRandomItemArticle) GetName() string { return v.Name }
+
+func (v *SimpleInlineFragmentRandomItemVideo) implementsGraphQLInterfaceSimpleInlineFragmentRandomItemContent() {
+}
+
+// GetTypename is a part of, and documented with, the interface SimpleInlineFragmentRandomItemContent.
+func (v *SimpleInlineFragmentRandomItemVideo) GetTypename() string { return v.Typename }
+
+// GetId is a part of, and documented with, the interface SimpleInlineFragmentRandomItemContent.
+func (v *SimpleInlineFragmentRandomItemVideo) GetId() testutil.ID { return v.Id }
+
+// GetName is a part of, and documented with, the interface SimpleInlineFragmentRandomItemContent.
+func (v *SimpleInlineFragmentRandomItemVideo) GetName() string { return v.Name }
+
+func (v *SimpleInlineFragmentRandomItemTopic) implementsGraphQLInterfaceSimpleInlineFragmentRandomItemContent() {
+}
+
+// GetTypename is a part of, and documented with, the interface SimpleInlineFragmentRandomItemContent.
+func (v *SimpleInlineFragmentRandomItemTopic) GetTypename() string { return v.Typename }
+
+// GetId is a part of, and documented with, the interface SimpleInlineFragmentRandomItemContent.
+func (v *SimpleInlineFragmentRandomItemTopic) GetId() testutil.ID { return v.Id }
+
+// GetName is a part of, and documented with, the interface SimpleInlineFragmentRandomItemContent.
+func (v *SimpleInlineFragmentRandomItemTopic) GetName() string { return v.Name }
+
+func __unmarshalSimpleInlineFragmentRandomItemContent(v *SimpleInlineFragmentRandomItemContent, m json.RawMessage) error {
+	if string(m) == "null" {
+		return nil
+	}
+
+	var tn struct {
+		TypeName string `json:"__typename"`
+	}
+	err := json.Unmarshal(m, &tn)
+	if err != nil {
+		return err
+	}
+
+	switch tn.TypeName {
+	case "Article":
+		*v = new(SimpleInlineFragmentRandomItemArticle)
+		return json.Unmarshal(m, *v)
+	case "Video":
+		*v = new(SimpleInlineFragmentRandomItemVideo)
+		return json.Unmarshal(m, *v)
+	case "Topic":
+		*v = new(SimpleInlineFragmentRandomItemTopic)
+		return json.Unmarshal(m, *v)
+	default:
+		return fmt.Errorf(
+			`Unexpected concrete type for SimpleInlineFragmentRandomItemContent: "%v"`, tn.TypeName)
+	}
+}
+
+// SimpleInlineFragmentRandomItemTopic includes the requested fields of the GraphQL type Topic.
+type SimpleInlineFragmentRandomItemTopic struct {
+	Typename string `json:"__typename"`
+	// ID is the identifier of the content.
+	Id   testutil.ID `json:"id"`
+	Name string      `json:"name"`
+}
+
+// SimpleInlineFragmentRandomItemVideo includes the requested fields of the GraphQL type Video.
+type SimpleInlineFragmentRandomItemVideo struct {
+	Typename string `json:"__typename"`
+	// ID is the identifier of the content.
+	Id       testutil.ID `json:"id"`
+	Name     string      `json:"name"`
+	Duration int         `json:"duration"`
+}
+
+// SimpleInlineFragmentResponse is returned by SimpleInlineFragment on success.
+type SimpleInlineFragmentResponse struct {
+	RandomItem SimpleInlineFragmentRandomItemContent `json:"-"`
+}
+
+func (v *SimpleInlineFragmentResponse) UnmarshalJSON(b []byte) error {
+
+	type SimpleInlineFragmentResponseWrapper SimpleInlineFragmentResponse
+
+	var firstPass struct {
+		*SimpleInlineFragmentResponseWrapper
+		RandomItem json.RawMessage `json:"randomItem"`
+	}
+	firstPass.SimpleInlineFragmentResponseWrapper = (*SimpleInlineFragmentResponseWrapper)(v)
+
+	err := json.Unmarshal(b, &firstPass)
+	if err != nil {
+		return err
+	}
+
+	{
+		target := &v.RandomItem
+		raw := firstPass.RandomItem
+		err = __unmarshalSimpleInlineFragmentRandomItemContent(
+			target, raw)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func SimpleInlineFragment(
+	client graphql.Client,
+) (*SimpleInlineFragmentResponse, error) {
+	var retval SimpleInlineFragmentResponse
+	err := client.MakeRequest(
+		nil,
+		"SimpleInlineFragment",
+		`
+query SimpleInlineFragment {
+	randomItem {
+		__typename
+		id
+		name
+		... on Article {
+			text
+		}
+		... on Video {
+			duration
+		}
+	}
+}
+`,
+		&retval,
+		nil,
+	)
+	return &retval, err
+}
+
diff --git a/generate/testdata/snapshots/TestGenerate-SimpleInlineFragment.graphql-SimpleInlineFragment.graphql.json b/generate/testdata/snapshots/TestGenerate-SimpleInlineFragment.graphql-SimpleInlineFragment.graphql.json
new file mode 100644
index 0000000..150cfa9
--- /dev/null
+++ b/generate/testdata/snapshots/TestGenerate-SimpleInlineFragment.graphql-SimpleInlineFragment.graphql.json
@@ -0,0 +1,9 @@
+{
+  "operations": [
+    {
+      "operationName": "SimpleInlineFragment",
+      "query": "\nquery SimpleInlineFragment {\n\trandomItem {\n\t\t__typename\n\t\tid\n\t\tname\n\t\t... on Article {\n\t\t\ttext\n\t\t}\n\t\t... on Video {\n\t\t\tduration\n\t\t}\n\t}\n}\n",
+      "sourceLocation": "testdata/queries/SimpleInlineFragment.graphql"
+    }
+  ]
+}
diff --git a/generate/testdata/snapshots/TestGenerate-UnionNoFragments.graphql-UnionNoFragments.graphql.go b/generate/testdata/snapshots/TestGenerate-UnionNoFragments.graphql-UnionNoFragments.graphql.go
index 43fe75b..da7013d 100644
--- a/generate/testdata/snapshots/TestGenerate-UnionNoFragments.graphql-UnionNoFragments.graphql.go
+++ b/generate/testdata/snapshots/TestGenerate-UnionNoFragments.graphql-UnionNoFragments.graphql.go
@@ -61,6 +61,9 @@ func __unmarshalUnionNoFragmentsQueryRandomLeafLeafContent(v *UnionNoFragmentsQu
 	case "Video":
 		*v = new(UnionNoFragmentsQueryRandomLeafVideo)
 		return json.Unmarshal(m, *v)
+	case "":
+		return fmt.Errorf(
+			"Response was missing LeafContent.__typename")
 	default:
 		return fmt.Errorf(
 			`Unexpected concrete type for UnionNoFragmentsQueryRandomLeafLeafContent: "%v"`, tn.TypeName)
@@ -98,7 +101,8 @@ func (v *UnionNoFragmentsQueryResponse) UnmarshalJSON(b []byte) error {
 		err = __unmarshalUnionNoFragmentsQueryRandomLeafLeafContent(
 			target, raw)
 		if err != nil {
-			return err
+			return fmt.Errorf(
+				"Unable to unmarshal UnionNoFragmentsQueryResponse.RandomLeaf: %w", err)
 		}
 	}
 	return nil
diff --git a/generate/testdata/snapshots/TestGenerate-unexported.graphql-unexported.graphql.go b/generate/testdata/snapshots/TestGenerate-unexported.graphql-unexported.graphql.go
index c07b814..f5c5b39 100644
--- a/generate/testdata/snapshots/TestGenerate-unexported.graphql-unexported.graphql.go
+++ b/generate/testdata/snapshots/TestGenerate-unexported.graphql-unexported.graphql.go
@@ -50,9 +50,10 @@ type userQueryInput struct {
 	Email string `json:"email"`
 	Name  string `json:"name"`
 	// id looks the user up by ID.  It's a great way to look up users.
-	Id    testutil.ID `json:"id"`
-	Role  Role        `json:"role"`
-	Names []string    `json:"names"`
+	Id         testutil.ID      `json:"id"`
+	Role       Role             `json:"role"`
+	Names      []string         `json:"names"`
+	HasPokemon testutil.Pokemon `json:"hasPokemon"`
 }
 
 func unexported(
diff --git a/generate/testdata/snapshots/TestGenerateErrors-ConflictingSelections.go b/generate/testdata/snapshots/TestGenerateErrors-ConflictingSelections.go
new file mode 100644
index 0000000..4b3033f
--- /dev/null
+++ b/generate/testdata/snapshots/TestGenerateErrors-ConflictingSelections.go
@@ -0,0 +1,1 @@
+testdata/errors/ConflictingSelections.go:4: operations must have operation-names
diff --git a/generate/testdata/snapshots/TestGenerateErrors-ConflictingSelections.graphql b/generate/testdata/snapshots/TestGenerateErrors-ConflictingSelections.graphql
new file mode 100644
index 0000000..b3bf989
--- /dev/null
+++ b/generate/testdata/snapshots/TestGenerateErrors-ConflictingSelections.graphql
@@ -0,0 +1,1 @@
+testdata/errors/ConflictingSelections.graphql:1: operations must have operation-names
diff --git a/generate/testdata/snapshots/TestGenerateErrors-UnknownScalar.go b/generate/testdata/snapshots/TestGenerateErrors-UnknownScalar.go
index c3d339b..3c698d2 100644
--- a/generate/testdata/snapshots/TestGenerateErrors-UnknownScalar.go
+++ b/generate/testdata/snapshots/TestGenerateErrors-UnknownScalar.go
@@ -1,1 +1,1 @@
-testdata/errors/UnknownScalar.schema.graphql:3: unknown scalar UnknownScalar: please add it to genqlient.yaml
+testdata/errors/UnknownScalar.schema.graphql:3: unknown scalar UnknownScalar: please add it to "bindings" in genqlient.yaml
diff --git a/generate/testdata/snapshots/TestGenerateErrors-UnknownScalar.graphql b/generate/testdata/snapshots/TestGenerateErrors-UnknownScalar.graphql
index c3d339b..3c698d2 100644
--- a/generate/testdata/snapshots/TestGenerateErrors-UnknownScalar.graphql
+++ b/generate/testdata/snapshots/TestGenerateErrors-UnknownScalar.graphql
@@ -1,1 +1,1 @@
-testdata/errors/UnknownScalar.schema.graphql:3: unknown scalar UnknownScalar: please add it to genqlient.yaml
+testdata/errors/UnknownScalar.schema.graphql:3: unknown scalar UnknownScalar: please add it to "bindings" in genqlient.yaml
diff --git a/internal/integration/integration_test.go b/internal/integration/integration_test.go
index b759ef3..de3578b 100644
--- a/internal/integration/integration_test.go
+++ b/internal/integration/integration_test.go
@@ -206,6 +206,91 @@ func TestInterfaceListPointerField(t *testing.T) {
 	assert.Nil(t, *resp.Beings[2])
 }
 
+func TestFragments(t *testing.T) {
+	_ = `# @genqlient
+	query queryWithFragments($ids: [ID!]!) {
+		beings(ids: $ids) {
+			__typename id
+			... on Being { id name }
+			... on Animal {
+				id
+				hair { hasHair }
+				species
+				owner {
+					id
+					... on Being { name }
+					... on User { luckyNumber }
+				}
+			}
+			... on Lucky { luckyNumber }
+			... on User { hair { color } }
+		}
+	}`
+
+	ctx := context.Background()
+	server := server.RunServer()
+	defer server.Close()
+	client := graphql.NewClient(server.URL, http.DefaultClient)
+
+	resp, err := queryWithFragments(ctx, client, []string{"1", "3", "12847394823"})
+	require.NoError(t, err)
+
+	require.Len(t, resp.Beings, 3)
+
+	// We should get the following three beings:
+	//	User{Id: 1, Name: "Yours Truly"},
+	//	Animal{Id: 3, Name: "Fido"},
+	//	null
+
+	// Check fields both via interface and via type-assertion when possible
+	// User has, in total, the fields: __typename id name luckyNumber.
+	assert.Equal(t, "User", resp.Beings[0].GetTypename())
+	assert.Equal(t, "1", resp.Beings[0].GetId())
+	assert.Equal(t, "Yours Truly", resp.Beings[0].GetName())
+	// (hair and luckyNumber we need to cast for)
+
+	user, ok := resp.Beings[0].(*queryWithFragmentsBeingsUser)
+	require.Truef(t, ok, "got %T, not User", resp.Beings[0])
+	assert.Equal(t, "1", user.Id)
+	assert.Equal(t, "Yours Truly", user.Name)
+	// TODO(benkraft): Uncomment once we fix the interface-field type-naming
+	// bug that's causing this to get the wrong type (because we end up
+	// generating two conflicting types).
+	//	assert.Equal(t, "Black", user.Hair.Color)
+	assert.Equal(t, 17, user.LuckyNumber)
+
+	// Animal has, in total, the fields:
+	//	__typename
+	//	id
+	//	species
+	//	owner {
+	//		id
+	//		name
+	//		... on User { luckyNumber }
+	//	}
+	assert.Equal(t, "Animal", resp.Beings[1].GetTypename())
+	assert.Equal(t, "3", resp.Beings[1].GetId())
+	// (hair, species, and owner.* we have to cast for)
+
+	animal, ok := resp.Beings[1].(*queryWithFragmentsBeingsAnimal)
+	require.Truef(t, ok, "got %T, not Animal", resp.Beings[1])
+	assert.Equal(t, "3", animal.Id)
+	assert.Equal(t, SpeciesDog, animal.Species)
+	assert.True(t, animal.Hair.HasHair)
+
+	assert.Equal(t, "1", animal.Owner.GetId())
+	assert.Equal(t, "Yours Truly", animal.Owner.GetName())
+	// (luckyNumber we have to cast for, again)
+
+	owner, ok := animal.Owner.(*queryWithFragmentsBeingsOwnerUser)
+	require.Truef(t, ok, "got %T, not User", animal.Owner)
+	assert.Equal(t, "1", owner.Id)
+	assert.Equal(t, "Yours Truly", owner.Name)
+	assert.Equal(t, 17, owner.LuckyNumber)
+
+	assert.Nil(t, resp.Beings[2])
+}
+
 func TestGeneratedCode(t *testing.T) {
 	// TODO(benkraft): Check that gqlgen is up to date too.  In practice that's
 	// less likely to be a problem, since it should only change if you update
diff --git a/internal/testutil/types.go b/internal/testutil/types.go
index b61b4e0..d5d5446 100644
--- a/internal/testutil/types.go
+++ b/internal/testutil/types.go
@@ -1,3 +1,12 @@
 package testutil
 
 type ID string
+
+type Pokemon struct {
+	Species string `json:"species"`
+	Level   int    `json:"level"`
+}
+
+func (p Pokemon) Battle(q Pokemon) bool {
+	return p.Level > q.Level
+}