Repository: salsa-rs/salsa (rust)

Issue:
Proposal: in `new` methods on intern structs, leverage `Borrow` or `ToOwned` traits or something
I often wind up with an `Identifier` interned struct:

```rust
#[salsa::interned]
struct Identifier<'db> { text: String }
```

and then I want to create an instance from an `&str`. It's silly that I have to allocate an owned string for that. The hashmap methods already support the ability to start with a borrowed value and "promote" to an owned value if needed, we should leverage that.

Pull request description:
Add a way to use reference-types in InternedStruct::new
Closes #583

Patch:
diff --git a/Cargo.toml b/Cargo.toml
index d3815b18..8a8e9063 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -10,7 +10,7 @@ description = "A generic framework for on-demand, incrementalized computation (e
 [dependencies]
 arc-swap = "1"
 crossbeam = "0.8"
-dashmap = "6"
+dashmap = { version = "6", features = ["raw-api"] }
 hashlink = "0.9"
 indexmap = "2"
 append-only-vec = "0.1.5"
diff --git a/components/salsa-macro-rules/src/setup_interned_struct.rs b/components/salsa-macro-rules/src/setup_interned_struct.rs
index 2b7f8d8f..bf9d98f5 100644
--- a/components/salsa-macro-rules/src/setup_interned_struct.rs
+++ b/components/salsa-macro-rules/src/setup_interned_struct.rs
@@ -32,6 +32,9 @@ macro_rules! setup_interned_struct {
         // Indices for each field from 0..N -- must be unsuffixed (e.g., `0`, `1`).
         field_indices: [$($field_index:tt),*],
 
+        // Indexed types for each field (T0, T1, ...)
+        field_indexed_tys: [$($indexed_ty:ident),*],
+
         // Number of fields
         num_fields: $N:literal,
 
@@ -62,10 +65,36 @@ macro_rules! setup_interned_struct {
 
             type $Configuration = $Struct<'static>;
 
+            type StructData<$db_lt> = ($($field_ty,)*);
+
+            /// Key to use during hash lookups. Each field is some type that implements `Lookup<T>`
+            /// for the owned type. This permits interning with an `&str` when a `String` is required and so forth.
+            struct StructKey<$db_lt, $($indexed_ty: $zalsa::interned::Lookup<$field_ty>),*>(
+                $($indexed_ty,)*
+                std::marker::PhantomData<&$db_lt ()>,
+            );
+
+            impl<$db_lt, $($indexed_ty: $zalsa::interned::Lookup<$field_ty>),*> $zalsa::interned::Lookup<StructData<$db_lt>>
+                for StructKey<$db_lt, $($indexed_ty),*> {
+
+                fn hash<H: std::hash::Hasher>(&self, h: &mut H) {
+                    $($zalsa::interned::Lookup::hash(&self.$field_index, &mut *h);)*
+                }
+
+                fn eq(&self, data: &StructData<$db_lt>) -> bool {
+                    ($($zalsa::interned::Lookup::eq(&self.$field_index, &data.$field_index) && )* true)
+                }
+
+                #[allow(unused_unit)]
+                fn into_owned(self) -> StructData<$db_lt> {
+                    ($($zalsa::interned::Lookup::into_owned(self.$field_index),)*)
+                }
+            }
+
             impl $zalsa_struct::Configuration for $Configuration {
                 const DEBUG_NAME: &'static str = stringify!($Struct);
-                type Data<$db_lt> = ($($field_ty,)*);
-                type Struct<$db_lt> = $Struct<$db_lt>;
+                type Data<'a> = StructData<'a>;
+                type Struct<'a> = $Struct<'a>;
                 fn struct_from_id<'db>(id: salsa::Id) -> Self::Struct<'db> {
                     $Struct(id, std::marker::PhantomData)
                 }
@@ -126,13 +155,14 @@ macro_rules! setup_interned_struct {
             }
 
             impl<$db_lt> $Struct<$db_lt> {
-                pub fn $new_fn<$Db>(db: &$db_lt $Db, $($field_id: $field_ty),*) -> Self
+                pub fn $new_fn<$Db>(db: &$db_lt $Db,  $($field_id: impl $zalsa::interned::Lookup<$field_ty>),*) -> Self
                 where
                     // FIXME(rust-lang/rust#65991): The `db` argument *should* have the type `dyn Database`
                     $Db: ?Sized + salsa::Database,
                 {
                     let current_revision = $zalsa::current_revision(db);
-                    $Configuration::ingredient(db).intern(db.as_dyn_database(), ($($field_id,)*))
+                    $Configuration::ingredient(db).intern(db.as_dyn_database(),
+                        StructKey::<$db_lt>($($field_id,)* std::marker::PhantomData::default()))
                 }
 
                 $(
diff --git a/components/salsa-macros/src/interned.rs b/components/salsa-macros/src/interned.rs
index b0fdb327..aea9a4e1 100644
--- a/components/salsa-macros/src/interned.rs
+++ b/components/salsa-macros/src/interned.rs
@@ -90,6 +90,7 @@ impl Macro {
         let field_getter_ids = salsa_struct.field_getter_ids();
         let field_options = salsa_struct.field_options();
         let field_tys = salsa_struct.field_tys();
+        let field_indexed_tys = salsa_struct.field_indexed_tys();
         let generate_debug_impl = salsa_struct.generate_debug_impl();
 
         let zalsa = self.hygiene.ident("zalsa");
@@ -112,6 +113,7 @@ impl Macro {
                     field_getters: [#(#field_vis #field_getter_ids),*],
                     field_tys: [#(#field_tys),*],
                     field_indices: [#(#field_indices),*],
+                    field_indexed_tys: [#(#field_indexed_tys),*],
                     num_fields: #num_fields,
                     generate_debug_impl: #generate_debug_impl,
                     unused_names: [
diff --git a/components/salsa-macros/src/salsa_struct.rs b/components/salsa-macros/src/salsa_struct.rs
index 54808240..b93470a4 100644
--- a/components/salsa-macros/src/salsa_struct.rs
+++ b/components/salsa-macros/src/salsa_struct.rs
@@ -242,6 +242,14 @@ where
         self.fields.iter().map(|f| &f.field.ty).collect()
     }
 
+    pub(crate) fn field_indexed_tys(&self) -> Vec<syn::Ident> {
+        self.fields
+            .iter()
+            .enumerate()
+            .map(|(i, _)| quote::format_ident!("T{i}"))
+            .collect()
+    }
+
     pub(crate) fn field_options(&self) -> Vec<TokenStream> {
         self.fields
             .iter()
diff --git a/src/interned.rs b/src/interned.rs
index 2003520c..94a6d896 100644
--- a/src/interned.rs
+++ b/src/interned.rs
@@ -1,7 +1,3 @@
-use std::fmt;
-use std::hash::Hash;
-use std::marker::PhantomData;
-
 use crate::durability::Durability;
 use crate::id::AsId;
 use crate::ingredient::fmt_index;
@@ -13,6 +9,10 @@ use crate::table::Slot;
 use crate::zalsa::IngredientIndex;
 use crate::zalsa_local::QueryOrigin;
 use crate::{Database, DatabaseKeyIndex, Id};
+use std::fmt;
+use std::hash::{BuildHasher, Hash, Hasher};
+use std::marker::PhantomData;
+use std::path::{Path, PathBuf};
 
 use super::hash::FxDashMap;
 use super::ingredient::Ingredient;
@@ -117,7 +117,7 @@ where
     pub fn intern_id<'db>(
         &'db self,
         db: &'db dyn crate::Database,
-        data: C::Data<'db>,
+        data: impl Lookup<C::Data<'db>>,
     ) -> crate::Id {
         C::deref_struct(self.intern(db, data)).as_id()
     }
@@ -126,7 +126,7 @@ where
     pub fn intern<'db>(
         &'db self,
         db: &'db dyn crate::Database,
-        data: C::Data<'db>,
+        data: impl Lookup<C::Data<'db>>,
     ) -> C::Struct<'db> {
         let zalsa_local = db.zalsa_local();
         zalsa_local.report_tracked_read(
@@ -137,12 +137,29 @@ where
 
         // Optimisation to only get read lock on the map if the data has already
         // been interned.
+        // We need to use the raw API for this lookup. See the [`Lookup`][] trait definition for an explanation of why.
+        let data_hash = {
+            let mut hasher = self.key_map.hasher().build_hasher();
+            data.hash(&mut hasher);
+            hasher.finish()
+        };
+        let shard = self.key_map.determine_shard(data_hash as _);
+        {
+            let lock = self.key_map.shards()[shard].read();
+            if let Some(bucket) = lock.find(data_hash, |(a, _)| {
+                // SAFETY: it's safe to go from Data<'static> to Data<'db>
+                // shrink lifetime here to use a single lifetime in Lookup::eq(&StructKey<'db>, &C::Data<'db>)
+                let a: &C::Data<'db> = unsafe { std::mem::transmute(a) };
+                Lookup::eq(&data, a)
+            }) {
+                // SAFETY: Read lock on map is held during this block
+                return C::struct_from_id(unsafe { *bucket.as_ref().1.get() });
+            }
+        };
+
+        let data = data.into_owned();
+
         let internal_data = unsafe { self.to_internal_data(data) };
-        if let Some(guard) = self.key_map.get(&internal_data) {
-            let id = *guard;
-            drop(guard);
-            return C::struct_from_id(id);
-        }
 
         match self.key_map.entry(internal_data.clone()) {
             // Data has been interned by a racing call, use that ID instead
@@ -288,3 +305,119 @@ where
         &self.syncs
     }
 }
+
+/// The `Lookup` trait is a more flexible variant on [`std::borrow::Borrow`]
+/// and [`std::borrow::ToOwned`].
+///
+/// It is implemented by "some type that can be used as the lookup key for `O`".
+/// This means that `self` can be hashed and compared for equality with values
+/// of type `O` without actually creating an owned value. It `self` needs to be interned,
+/// it can be converted into an equivalent value of type `O`.
+///
+/// The canonical example is `&str: Lookup<String>`. However, this example
+/// alone can be handled by [`std::borrow::Borrow`][]. In our case, we may have
+/// multiple keys accumulated into a struct, like `ViewStruct: Lookup<(K1, ...)>`,
+/// where `struct ViewStruct<L1: Lookup<K1>...>(K1...)`. The `Borrow` trait
+/// requires that `&(K1...)` be convertible to `&ViewStruct` which just isn't
+/// possible. `Lookup` instead offers direct `hash` and `eq` methods.
+pub trait Lookup<O> {
+    fn hash<H: Hasher>(&self, h: &mut H);
+    fn eq(&self, data: &O) -> bool;
+    fn into_owned(self) -> O;
+}
+
+impl<T> Lookup<T> for T
+where
+    T: Hash + Eq,
+{
+    fn hash<H: Hasher>(&self, h: &mut H) {
+        Hash::hash(self, &mut *h);
+    }
+
+    fn eq(&self, data: &T) -> bool {
+        self == data
+    }
+
+    fn into_owned(self) -> T {
+        self
+    }
+}
+
+impl<T> Lookup<T> for &T
+where
+    T: Clone + Eq + Hash,
+{
+    fn hash<H: Hasher>(&self, h: &mut H) {
+        Hash::hash(self, &mut *h);
+    }
+
+    fn eq(&self, data: &T) -> bool {
+        *self == data
+    }
+
+    fn into_owned(self) -> T {
+        Clone::clone(self)
+    }
+}
+
+impl Lookup<String> for &str {
+    fn hash<H: Hasher>(&self, h: &mut H) {
+        Hash::hash(self, &mut *h)
+    }
+
+    fn eq(&self, data: &String) -> bool {
+        self == data
+    }
+
+    fn into_owned(self) -> String {
+        self.to_owned()
+    }
+}
+
+impl<A: Hash + Eq + PartialEq<T> + Clone + Lookup<T>, T> Lookup<Vec<T>> for &[A] {
+    fn hash<H: Hasher>(&self, h: &mut H) {
+        for a in *self {
+            Hash::hash(a, h);
+        }
+    }
+
+    fn eq(&self, data: &Vec<T>) -> bool {
+        self.len() == data.len() && data.iter().enumerate().all(|(i, a)| &self[i] == a)
+    }
+
+    fn into_owned(self) -> Vec<T> {
+        self.iter().map(|a| Lookup::into_owned(a.clone())).collect()
+    }
+}
+
+impl<const N: usize, A: Hash + Eq + PartialEq<T> + Clone + Lookup<T>, T> Lookup<Vec<T>> for [A; N] {
+    fn hash<H: Hasher>(&self, h: &mut H) {
+        for a in self {
+            Hash::hash(a, h);
+        }
+    }
+
+    fn eq(&self, data: &Vec<T>) -> bool {
+        self.len() == data.len() && data.iter().enumerate().all(|(i, a)| &self[i] == a)
+    }
+
+    fn into_owned(self) -> Vec<T> {
+        self.into_iter()
+            .map(|a| Lookup::into_owned(a.clone()))
+            .collect()
+    }
+}
+
+impl Lookup<PathBuf> for &Path {
+    fn hash<H: Hasher>(&self, h: &mut H) {
+        Hash::hash(self, h);
+    }
+
+    fn eq(&self, data: &PathBuf) -> bool {
+        self == data
+    }
+
+    fn into_owned(self) -> PathBuf {
+        self.to_owned()
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index c23d9c2e..0ee7d3ec 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -132,6 +132,7 @@ pub mod plumbing {
         pub use crate::interned::Configuration;
         pub use crate::interned::IngredientImpl;
         pub use crate::interned::JarImpl;
+        pub use crate::interned::Lookup;
         pub use crate::interned::Value;
     }
 


Test patch:
diff --git a/tests/interned-struct-with-lifetime.rs b/tests/interned-struct-with-lifetime.rs
deleted file mode 100644
index a74d2c42..00000000
--- a/tests/interned-struct-with-lifetime.rs
+++ /dev/null
@@ -1,31 +0,0 @@
-//! Test that a `tracked` fn on a `salsa::input`
-//! compiles and executes successfully.
-
-use expect_test::expect;
-use test_log::test;
-
-#[salsa::interned]
-struct InternedString<'db> {
-    data: String,
-}
-
-#[salsa::interned]
-struct InternedPair<'db> {
-    data: (InternedString<'db>, InternedString<'db>),
-}
-
-#[salsa::tracked]
-fn intern_stuff(db: &dyn salsa::Database) -> String {
-    let s1 = InternedString::new(db, "Hello, ".to_string());
-    let s2 = InternedString::new(db, "World, ".to_string());
-    let s3 = InternedPair::new(db, (s1, s2));
-    format!("{s3:?}")
-}
-
-#[test]
-fn execute() {
-    let db = salsa::DatabaseImpl::new();
-    expect![[r#"
-        "InternedPair { data: (InternedString { data: \"Hello, \" }, InternedString { data: \"World, \" }) }"
-    "#]].assert_debug_eq(&intern_stuff(&db));
-}
diff --git a/tests/interned-structs.rs b/tests/interned-structs.rs
new file mode 100644
index 00000000..70dbc263
--- /dev/null
+++ b/tests/interned-structs.rs
@@ -0,0 +1,105 @@
+//! Test that a `tracked` fn on a `salsa::input`
+//! compiles and executes successfully.
+
+use expect_test::expect;
+use std::path::{Path, PathBuf};
+use test_log::test;
+
+#[salsa::interned]
+struct InternedString<'db> {
+    data: String,
+}
+
+#[salsa::interned]
+struct InternedPair<'db> {
+    data: (InternedString<'db>, InternedString<'db>),
+}
+
+#[salsa::interned]
+struct InternedTwoFields<'db> {
+    data1: String,
+    data2: String,
+}
+
+#[salsa::interned]
+struct InternedVec<'db> {
+    data1: Vec<String>,
+}
+
+#[salsa::interned]
+struct InternedPathBuf<'db> {
+    data1: PathBuf,
+}
+
+#[salsa::tracked]
+fn intern_stuff(db: &dyn salsa::Database) -> String {
+    let s1 = InternedString::new(db, "Hello, ".to_string());
+    let s2 = InternedString::new(db, "World, ");
+    let s3 = InternedPair::new(db, (s1, s2));
+
+    format!("{s3:?}")
+}
+
+#[test]
+fn execute() {
+    let db = salsa::DatabaseImpl::new();
+    expect![[r#"
+        "InternedPair { data: (InternedString { data: \"Hello, \" }, InternedString { data: \"World, \" }) }"
+    "#]].assert_debug_eq(&intern_stuff(&db));
+}
+
+#[test]
+fn interning_returns_equal_keys_for_equal_data() {
+    let db = salsa::DatabaseImpl::new();
+    let s1 = InternedString::new(&db, "Hello, ".to_string());
+    let s2 = InternedString::new(&db, "World, ".to_string());
+    let s1_2 = InternedString::new(&db, "Hello, ");
+    let s2_2 = InternedString::new(&db, "World, ");
+    assert_eq!(s1, s1_2);
+    assert_eq!(s2, s2_2);
+}
+#[test]
+fn interning_returns_equal_keys_for_equal_data_multi_field() {
+    let db = salsa::DatabaseImpl::new();
+    let s1 = InternedTwoFields::new(&db, "Hello, ".to_string(), "World");
+    let s2 = InternedTwoFields::new(&db, "World, ", "Hello".to_string());
+    let s1_2 = InternedTwoFields::new(&db, "Hello, ", "World");
+    let s2_2 = InternedTwoFields::new(&db, "World, ", "Hello");
+    let new = InternedTwoFields::new(&db, "Hello, World", "");
+
+    assert_eq!(s1, s1_2);
+    assert_eq!(s2, s2_2);
+    assert_ne!(s1, s2_2);
+    assert_ne!(s1, new);
+}
+
+#[test]
+fn interning_vec() {
+    let db = salsa::DatabaseImpl::new();
+    let s1 = InternedVec::new(&db, ["Hello, ".to_string(), "World".to_string()].as_slice());
+    let s2 = InternedVec::new(&db, ["Hello, ", "World"].as_slice());
+    let s3 = InternedVec::new(&db, vec!["Hello, ".to_string(), "World".to_string()]);
+    let s4 = InternedVec::new(&db, ["Hello, ", "World"].as_slice());
+    let s5 = InternedVec::new(&db, ["Hello, ", "World", "Test"].as_slice());
+    let s6 = InternedVec::new(&db, ["Hello, ", "World", ""].as_slice());
+    let s7 = InternedVec::new(&db, ["Hello, "].as_slice());
+    assert_eq!(s1, s2);
+    assert_eq!(s1, s3);
+    assert_eq!(s1, s4);
+    assert_ne!(s1, s5);
+    assert_ne!(s1, s6);
+    assert_ne!(s5, s6);
+    assert_ne!(s6, s7);
+}
+
+#[test]
+fn interning_path_buf() {
+    let db = salsa::DatabaseImpl::new();
+    let s1 = InternedPathBuf::new(&db, PathBuf::from("test_path".to_string()));
+    let s2 = InternedPathBuf::new(&db, Path::new("test_path"));
+    let s3 = InternedPathBuf::new(&db, Path::new("test_path/"));
+    let s4 = InternedPathBuf::new(&db, Path::new("test_path/a"));
+    assert_eq!(s1, s2);
+    assert_eq!(s1, s3);
+    assert_ne!(s1, s4);
+}