Repository: rust-analyzer/rust-analyzer (rust)

Issue:
Labels on breaks ignored for inference
Contrived example:
```rust
fn foo() {
    let _x = || 'outer: loop {
        let inner = 'inner: loop {
            let i = Default::default();
            if (break 'outer i) {
                loop { break 'inner 5i8; };
            } else if true {
                break 'inner 6;
            }
            break 7;
        };
        break inner < 8;
    };
}
```

rust-analyzer currently infers `inner`, `i`, `6`, `7`, and `8` to be of type `i32`. Correct would be `inner`, `6`, `7`: `i8` and `i`: `bool`.

I briefly looked into this and decided it would be necessary to extend the [HIR Expr](https://github.com/rust-analyzer/rust-analyzer/blob/5f7225446e75509ae0d971a6f3e2b9d3e37d6f2a/crates/ra_hir_def/src/expr.rs#L43) with block labels / break/continue targets. The [AST](https://github.com/rust-analyzer/rust-analyzer/blob/5f7225446e75509ae0d971a6f3e2b9d3e37d6f2a/crates/ra_syntax/src/ast/generated/nodes.rs#L1058) currently only offers the pseudo-lifetimes as `SyntaxToken`s. What would be a good type to represent the labels in the HIR?

Pull request description:
Infer labelled breaks correctly
Fixes #4663.

Patch:
diff --git a/crates/ra_hir_def/src/body/lower.rs b/crates/ra_hir_def/src/body/lower.rs
index 905c0cf5da..f159f80af0 100644
--- a/crates/ra_hir_def/src/body/lower.rs
+++ b/crates/ra_hir_def/src/body/lower.rs
@@ -134,7 +134,7 @@ impl ExprCollector<'_> {
         self.make_expr(expr, Err(SyntheticSyntax))
     }
     fn empty_block(&mut self) -> ExprId {
-        self.alloc_expr_desugared(Expr::Block { statements: Vec::new(), tail: None })
+        self.alloc_expr_desugared(Expr::Block { statements: Vec::new(), tail: None, label: None })
     }
     fn missing_expr(&mut self) -> ExprId {
         self.alloc_expr_desugared(Expr::Missing)
@@ -215,7 +215,16 @@ impl ExprCollector<'_> {
             ast::Expr::BlockExpr(e) => self.collect_block(e),
             ast::Expr::LoopExpr(e) => {
                 let body = self.collect_block_opt(e.loop_body());
-                self.alloc_expr(Expr::Loop { body }, syntax_ptr)
+                self.alloc_expr(
+                    Expr::Loop {
+                        body,
+                        label: e
+                            .label()
+                            .and_then(|l| l.lifetime_token())
+                            .map(|l| Name::new_lifetime(&l)),
+                    },
+                    syntax_ptr,
+                )
             }
             ast::Expr::WhileExpr(e) => {
                 let body = self.collect_block_opt(e.loop_body());
@@ -230,25 +239,56 @@ impl ExprCollector<'_> {
                             let pat = self.collect_pat(pat);
                             let match_expr = self.collect_expr_opt(condition.expr());
                             let placeholder_pat = self.missing_pat();
-                            let break_ = self.alloc_expr_desugared(Expr::Break { expr: None });
+                            let break_ =
+                                self.alloc_expr_desugared(Expr::Break { expr: None, label: None });
                             let arms = vec![
                                 MatchArm { pat, expr: body, guard: None },
                                 MatchArm { pat: placeholder_pat, expr: break_, guard: None },
                             ];
                             let match_expr =
                                 self.alloc_expr_desugared(Expr::Match { expr: match_expr, arms });
-                            return self.alloc_expr(Expr::Loop { body: match_expr }, syntax_ptr);
+                            return self.alloc_expr(
+                                Expr::Loop {
+                                    body: match_expr,
+                                    label: e
+                                        .label()
+                                        .and_then(|l| l.lifetime_token())
+                                        .map(|l| Name::new_lifetime(&l)),
+                                },
+                                syntax_ptr,
+                            );
                         }
                     },
                 };
 
-                self.alloc_expr(Expr::While { condition, body }, syntax_ptr)
+                self.alloc_expr(
+                    Expr::While {
+                        condition,
+                        body,
+                        label: e
+                            .label()
+                            .and_then(|l| l.lifetime_token())
+                            .map(|l| Name::new_lifetime(&l)),
+                    },
+                    syntax_ptr,
+                )
             }
             ast::Expr::ForExpr(e) => {
                 let iterable = self.collect_expr_opt(e.iterable());
                 let pat = self.collect_pat_opt(e.pat());
                 let body = self.collect_block_opt(e.loop_body());
-                self.alloc_expr(Expr::For { iterable, pat, body }, syntax_ptr)
+                self.alloc_expr(
+                    Expr::For {
+                        iterable,
+                        pat,
+                        body,
+                        label: e
+                            .label()
+                            .and_then(|l| l.lifetime_token())
+                            .map(|l| Name::new_lifetime(&l)),
+                    },
+                    syntax_ptr,
+                )
             }
             ast::Expr::CallExpr(e) => {
                 let callee = self.collect_expr_opt(e.expr());
@@ -301,13 +341,16 @@ impl ExprCollector<'_> {
                     .unwrap_or(Expr::Missing);
                 self.alloc_expr(path, syntax_ptr)
             }
-            ast::Expr::ContinueExpr(_e) => {
-                // FIXME: labels
-                self.alloc_expr(Expr::Continue, syntax_ptr)
-            }
+            ast::Expr::ContinueExpr(e) => self.alloc_expr(
+                Expr::Continue { label: e.lifetime_token().map(|l| Name::new_lifetime(&l)) },
+                syntax_ptr,
+            ),
             ast::Expr::BreakExpr(e) => {
                 let expr = e.expr().map(|e| self.collect_expr(e));
-                self.alloc_expr(Expr::Break { expr }, syntax_ptr)
+                self.alloc_expr(
+                    Expr::Break { expr, label: e.lifetime_token().map(|l| Name::new_lifetime(&l)) },
+                    syntax_ptr,
+                )
             }
             ast::Expr::ParenExpr(e) => {
                 let inner = self.collect_expr_opt(e.expr());
@@ -529,7 +572,8 @@ impl ExprCollector<'_> {
             })
             .collect();
         let tail = block.expr().map(|e| self.collect_expr(e));
-        self.alloc_expr(Expr::Block { statements, tail }, syntax_node_ptr)
+        let label = block.label().and_then(|l| l.lifetime_token()).map(|t| Name::new_lifetime(&t));
+        self.alloc_expr(Expr::Block { statements, tail, label }, syntax_node_ptr)
     }
 
     fn collect_block_items(&mut self, block: &ast::BlockExpr) {
diff --git a/crates/ra_hir_def/src/body/scope.rs b/crates/ra_hir_def/src/body/scope.rs
index 09e92b74e1..e48ff38f96 100644
--- a/crates/ra_hir_def/src/body/scope.rs
+++ b/crates/ra_hir_def/src/body/scope.rs
@@ -138,10 +138,10 @@ fn compute_block_scopes(
 fn compute_expr_scopes(expr: ExprId, body: &Body, scopes: &mut ExprScopes, scope: ScopeId) {
     scopes.set_scope(expr, scope);
     match &body[expr] {
-        Expr::Block { statements, tail } => {
+        Expr::Block { statements, tail, .. } => {
             compute_block_scopes(&statements, *tail, body, scopes, scope);
         }
-        Expr::For { iterable, pat, body: body_expr } => {
+        Expr::For { iterable, pat, body: body_expr, .. } => {
             compute_expr_scopes(*iterable, body, scopes, scope);
             let scope = scopes.new_scope(scope);
             scopes.add_bindings(body, scope, *pat);
diff --git a/crates/ra_hir_def/src/expr.rs b/crates/ra_hir_def/src/expr.rs
index f25c6f9580..ca49b26d15 100644
--- a/crates/ra_hir_def/src/expr.rs
+++ b/crates/ra_hir_def/src/expr.rs
@@ -52,18 +52,22 @@ pub enum Expr {
     Block {
         statements: Vec<Statement>,
         tail: Option<ExprId>,
+        label: Option<Name>,
     },
     Loop {
         body: ExprId,
+        label: Option<Name>,
     },
     While {
         condition: ExprId,
         body: ExprId,
+        label: Option<Name>,
     },
     For {
         iterable: ExprId,
         pat: PatId,
         body: ExprId,
+        label: Option<Name>,
     },
     Call {
         callee: ExprId,
@@ -79,9 +83,12 @@ pub enum Expr {
         expr: ExprId,
         arms: Vec<MatchArm>,
     },
-    Continue,
+    Continue {
+        label: Option<Name>,
+    },
     Break {
         expr: Option<ExprId>,
+        label: Option<Name>,
     },
     Return {
         expr: Option<ExprId>,
@@ -225,7 +232,7 @@ impl Expr {
                     f(*else_branch);
                 }
             }
-            Expr::Block { statements, tail } => {
+            Expr::Block { statements, tail, .. } => {
                 for stmt in statements {
                     match stmt {
                         Statement::Let { initializer, .. } => {
@@ -241,8 +248,8 @@ impl Expr {
                 }
             }
             Expr::TryBlock { body } => f(*body),
-            Expr::Loop { body } => f(*body),
-            Expr::While { condition, body } => {
+            Expr::Loop { body, .. } => f(*body),
+            Expr::While { condition, body, .. } => {
                 f(*condition);
                 f(*body);
             }
@@ -268,8 +275,8 @@ impl Expr {
                     f(arm.expr);
                 }
             }
-            Expr::Continue => {}
-            Expr::Break { expr } | Expr::Return { expr } => {
+            Expr::Continue { .. } => {}
+            Expr::Break { expr, .. } | Expr::Return { expr } => {
                 if let Some(expr) = expr {
                     f(*expr);
                 }
diff --git a/crates/ra_hir_expand/src/name.rs b/crates/ra_hir_expand/src/name.rs
index fecce224ee..ea495cb11a 100644
--- a/crates/ra_hir_expand/src/name.rs
+++ b/crates/ra_hir_expand/src/name.rs
@@ -37,6 +37,11 @@ impl Name {
         Name(Repr::TupleField(idx))
     }
 
+    pub fn new_lifetime(lt: &ra_syntax::SyntaxToken) -> Name {
+        assert!(lt.kind() == ra_syntax::SyntaxKind::LIFETIME);
+        Name(Repr::Text(lt.text().clone()))
+    }
+
     /// Shortcut to create inline plain text name
     const fn new_inline_ascii(text: &[u8]) -> Name {
         Name::new_text(SmolStr::new_inline_from_ascii(text.len(), text))
diff --git a/crates/ra_hir_ty/src/infer.rs b/crates/ra_hir_ty/src/infer.rs
index 957d6e0b57..dc77e88e50 100644
--- a/crates/ra_hir_ty/src/infer.rs
+++ b/crates/ra_hir_ty/src/infer.rs
@@ -219,6 +219,17 @@ struct InferenceContext<'a> {
 struct BreakableContext {
     pub may_break: bool,
     pub break_ty: Ty,
+    pub label: Option<name::Name>,
+}
+
+fn find_breakable<'c>(
+    ctxs: &'c mut [BreakableContext],
+    label: Option<&name::Name>,
+) -> Option<&'c mut BreakableContext> {
+    match label {
+        Some(_) => ctxs.iter_mut().rev().find(|ctx| ctx.label.as_ref() == label),
+        None => ctxs.last_mut(),
+    }
 }
 
 impl<'a> InferenceContext<'a> {
diff --git a/crates/ra_hir_ty/src/infer/expr.rs b/crates/ra_hir_ty/src/infer/expr.rs
index 78084cb573..4a98e2debf 100644
--- a/crates/ra_hir_ty/src/infer/expr.rs
+++ b/crates/ra_hir_ty/src/infer/expr.rs
@@ -22,8 +22,8 @@ use crate::{
 };
 
 use super::{
-    BindingMode, BreakableContext, Diverges, Expectation, InferenceContext, InferenceDiagnostic,
-    TypeMismatch,
+    find_breakable, BindingMode, BreakableContext, Diverges, Expectation, InferenceContext,
+    InferenceDiagnostic, TypeMismatch,
 };
 
 impl<'a> InferenceContext<'a> {
@@ -86,16 +86,20 @@ impl<'a> InferenceContext<'a> {
 
                 self.coerce_merge_branch(&then_ty, &else_ty)
             }
-            Expr::Block { statements, tail } => self.infer_block(statements, *tail, expected),
+            Expr::Block { statements, tail, .. } => {
+                // FIXME: Breakable block inference
+                self.infer_block(statements, *tail, expected)
+            }
             Expr::TryBlock { body } => {
                 let _inner = self.infer_expr(*body, expected);
                 // FIXME should be std::result::Result<{inner}, _>
                 Ty::Unknown
             }
-            Expr::Loop { body } => {
+            Expr::Loop { body, label } => {
                 self.breakables.push(BreakableContext {
                     may_break: false,
                     break_ty: self.table.new_type_var(),
+                    label: label.clone(),
                 });
                 self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
 
@@ -110,8 +114,12 @@ impl<'a> InferenceContext<'a> {
                     Ty::simple(TypeCtor::Never)
                 }
             }
-            Expr::While { condition, body } => {
-                self.breakables.push(BreakableContext { may_break: false, break_ty: Ty::Unknown });
+            Expr::While { condition, body, label } => {
+                self.breakables.push(BreakableContext {
+                    may_break: false,
+                    break_ty: Ty::Unknown,
+                    label: label.clone(),
+                });
                 // while let is desugared to a match loop, so this is always simple while
                 self.infer_expr(*condition, &Expectation::has_type(Ty::simple(TypeCtor::Bool)));
                 self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
@@ -120,10 +128,14 @@ impl<'a> InferenceContext<'a> {
                 self.diverges = Diverges::Maybe;
                 Ty::unit()
             }
-            Expr::For { iterable, body, pat } => {
+            Expr::For { iterable, body, pat, label } => {
                 let iterable_ty = self.infer_expr(*iterable, &Expectation::none());
 
-                self.breakables.push(BreakableContext { may_break: false, break_ty: Ty::Unknown });
+                self.breakables.push(BreakableContext {
+                    may_break: false,
+                    break_ty: Ty::Unknown,
+                    label: label.clone(),
+                });
                 let pat_ty =
                     self.resolve_associated_type(iterable_ty, self.resolve_into_iter_item());
 
@@ -236,23 +248,24 @@ impl<'a> InferenceContext<'a> {
                 let resolver = resolver_for_expr(self.db.upcast(), self.owner, tgt_expr);
                 self.infer_path(&resolver, p, tgt_expr.into()).unwrap_or(Ty::Unknown)
             }
-            Expr::Continue => Ty::simple(TypeCtor::Never),
-            Expr::Break { expr } => {
+            Expr::Continue { .. } => Ty::simple(TypeCtor::Never),
+            Expr::Break { expr, label } => {
                 let val_ty = if let Some(expr) = expr {
                     self.infer_expr(*expr, &Expectation::none())
                 } else {
                     Ty::unit()
                 };
 
-                let last_ty = if let Some(ctxt) = self.breakables.last() {
-                    ctxt.break_ty.clone()
-                } else {
-                    Ty::Unknown
-                };
+                let last_ty =
+                    if let Some(ctxt) = find_breakable(&mut self.breakables, label.as_ref()) {
+                        ctxt.break_ty.clone()
+                    } else {
+                        Ty::Unknown
+                    };
 
                 let merged_type = self.coerce_merge_branch(&last_ty, &val_ty);
 
-                if let Some(ctxt) = self.breakables.last_mut() {
+                if let Some(ctxt) = find_breakable(&mut self.breakables, label.as_ref()) {
                     ctxt.break_ty = merged_type;
                     ctxt.may_break = true;
                 } else {
diff --git a/crates/ra_syntax/src/ast/generated/nodes.rs b/crates/ra_syntax/src/ast/generated/nodes.rs
index 255402fbce..cb430ca013 100644
--- a/crates/ra_syntax/src/ast/generated/nodes.rs
+++ b/crates/ra_syntax/src/ast/generated/nodes.rs
@@ -1081,6 +1081,7 @@ pub struct BlockExpr {
 impl ast::AttrsOwner for BlockExpr {}
 impl ast::ModuleItemOwner for BlockExpr {}
 impl BlockExpr {
+    pub fn label(&self) -> Option<Label> { support::child(&self.syntax) }
     pub fn l_curly_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T!['{']) }
     pub fn statements(&self) -> AstChildren<Stmt> { support::children(&self.syntax) }
     pub fn expr(&self) -> Option<Expr> { support::child(&self.syntax) }
diff --git a/xtask/src/ast_src.rs b/xtask/src/ast_src.rs
index d4621930ed..f60f0fb16c 100644
--- a/xtask/src/ast_src.rs
+++ b/xtask/src/ast_src.rs
@@ -1058,7 +1058,7 @@ pub(crate) const AST_SRC: AstSrc = AstSrc {
         /// [Reference](https://doc.rust-lang.org/reference/expressions/block-expr.html)
         /// [Labels for blocks RFC](https://github.com/rust-lang/rfcs/blob/master/text/2046-label-break-value.md)
         struct BlockExpr: AttrsOwner, ModuleItemOwner {
-            T!['{'], statements: [Stmt], Expr, T!['}'],
+            Label, T!['{'], statements: [Stmt], Expr, T!['}'],
         }
 
         /// Return expression.


Test patch:
diff --git a/crates/ra_hir_ty/src/tests/simple.rs b/crates/ra_hir_ty/src/tests/simple.rs
index 839491b9e2..88309157b7 100644
--- a/crates/ra_hir_ty/src/tests/simple.rs
+++ b/crates/ra_hir_ty/src/tests/simple.rs
@@ -1943,3 +1943,57 @@ fn test() {
     "###
     );
 }
+
+#[test]
+fn infer_labelled_break_with_val() {
+    assert_snapshot!(
+        infer(r#"
+fn foo() {
+    let _x = || 'outer: loop {
+        let inner = 'inner: loop {
+            let i = Default::default();
+            if (break 'outer i) {
+                loop { break 'inner 5i8; };
+            } else if true {
+                break 'inner 6;
+            }
+            break 7;
+        };
+        break inner < 8;
+    };
+}
+"#),
+        @r###"
+    10..336 '{     ...  }; }': ()
+    20..22 '_x': || -> bool
+    25..333 '|| 'ou...     }': || -> bool
+    28..333 ''outer...     }': bool
+    41..333 '{     ...     }': ()
+    55..60 'inner': i8
+    63..301 ''inner...     }': i8
+    76..301 '{     ...     }': ()
+    94..95 'i': bool
+    98..114 'Defaul...efault': {unknown}
+    98..116 'Defaul...ault()': bool
+    130..270 'if (br...     }': ()
+    134..148 'break 'outer i': !
+    147..148 'i': bool
+    150..209 '{     ...     }': ()
+    168..194 'loop {...5i8; }': !
+    173..194 '{ brea...5i8; }': ()
+    175..191 'break ...er 5i8': !
+    188..191 '5i8': i8
+    215..270 'if tru...     }': ()
+    218..222 'true': bool
+    223..270 '{     ...     }': ()
+    241..255 'break 'inner 6': !
+    254..255 '6': i8
+    283..290 'break 7': !
+    289..290 '7': i8
+    311..326 'break inner < 8': !
+    317..322 'inner': i8
+    317..326 'inner < 8': bool
+    325..326 '8': i8
+    "###
+    );
+}