Merge pull request #21226 from benodiwal/fix/impl-display-trait-generic-args

fix: fixed Impl display to show trait generic args

Author: ChayimFriedman2

crates/hir/src/display.rs

@@ -192,9 +192,11 @@ fn write_impl_header<'db>(impl_: &Impl, f: &mut HirFormatter<'_, 'db>) -> Result
     let def_id = GenericDefId::ImplId(impl_.id);
     write_generic_params(def_id, f)?;
 
-    if let Some(trait_) = impl_.trait_(db) {
-        let trait_data = db.trait_signature(trait_.id);
-        write!(f, " {} for", trait_data.name.display(db, f.edition()))?;
+    let impl_data = db.impl_signature(impl_.id);
+    if let Some(target_trait) = &impl_data.target_trait {
+        f.write_char(' ')?;
+        hir_display_with_store(&impl_data.store[target_trait.path], &impl_data.store).hir_fmt(f)?;
+        f.write_str(" for")?;
     }
 
     f.write_char(' ')?;

crates/ide/src/hover/tests.rs

@@ -11169,3 +11169,60 @@ fn foo() {
         "#]],
     );
 }
+
+#[test]
+fn hover_trait_impl_shows_generic_args() {
+    // Single generic arg
+    check(
+        r#"
+trait Foo<T> {
+    fn foo(&self) {}
+}
+
+impl<T> Foo<()> for T {
+    fn fo$0o(&self) {}
+}
+
+fn bar() {
+    ().foo();
+}
+"#,
+        expect![[r#"
+            *foo*
+
+            ```rust
+            ra_test_fixture
+            ```
+
+            ```rust
+            impl<T> Foo<()> for T
+            fn foo(&self)
+            ```
+        "#]],
+    );
+
+    // Multiple generic args
+    check(
+        r#"
+trait Foo<A, B> {
+    fn foo(&self) {}
+}
+
+impl<T> Foo<i32, u64> for T {
+    fn fo$0o(&self) {}
+}
+"#,
+        expect![[r#"
+            *foo*
+
+            ```rust
+            ra_test_fixture
+            ```
+
+            ```rust
+            impl<T> Foo<i32, u64> for T
+            fn foo(&self)
+            ```
+        "#]],
+    );
+}