Auto merge of rust-lang#16544 - dfireBird:impl_trait_completion, r=Veykril

Add completions to show only traits in trait `impl` statement

This is prerequisite PR for adding the assist mentioned in rust-lang#12500

P.S: If wanted, I will add the implementation of the assist in this PR as well.

Author: bors

crates/ide-completion/src/completions/flyimport.rs

@@ -238,6 +238,8 @@ fn import_on_the_fly(
             (PathKind::Type { location }, ItemInNs::Types(ty)) => {
                 if matches!(location, TypeLocation::TypeBound) {
                     matches!(ty, ModuleDef::Trait(_))
+                } else if matches!(location, TypeLocation::ImplTrait) {
+                    matches!(ty, ModuleDef::Trait(_) | ModuleDef::Module(_))
                 } else {
                     true
                 }

crates/ide-completion/src/completions/type.rs

@@ -31,6 +31,11 @@ pub(crate) fn complete_type_path(
             ScopeDef::ImplSelfType(_) => location.complete_self_type(),
             // Don't suggest attribute macros and derives.
             ScopeDef::ModuleDef(Macro(mac)) => mac.is_fn_like(ctx.db),
+            ScopeDef::ModuleDef(Trait(_) | Module(_))
+                if matches!(location, TypeLocation::ImplTrait) =>
+            {
+                true
+            }
             // Type things are fine
             ScopeDef::ModuleDef(
                 BuiltinType(_) | Adt(_) | Module(_) | Trait(_) | TraitAlias(_) | TypeAlias(_),
@@ -184,6 +189,21 @@ pub(crate) fn complete_type_path(
                         }
                     }
                 }
+                TypeLocation::ImplTrait => {
+                    acc.add_nameref_keywords_with_colon(ctx);
+                    ctx.process_all_names(&mut |name, def, doc_aliases| {
+                        let is_trait_or_module = matches!(
+                            def,
+                            ScopeDef::ModuleDef(
+                                hir::ModuleDef::Module(_) | hir::ModuleDef::Trait(_)
+                            )
+                        );
+                        if is_trait_or_module {
+                            acc.add_path_resolution(ctx, path_ctx, name, def, doc_aliases);
+                        }
+                    });
+                    return;
+                }
                 _ => {}
             };
 

crates/ide-completion/src/context.rs

@@ -202,6 +202,7 @@ impl TypeLocation {
             }
             TypeLocation::AssocConstEq => false,
             TypeLocation::AssocTypeEq => true,
+            TypeLocation::ImplTrait => false,
             _ => true,
         }
     }

crates/ide-completion/src/tests/flyimport.rs

@@ -1397,3 +1397,22 @@ pub use bridge2::server2::Span2;
         "#]],
     );
 }
+
+#[test]
+fn flyimport_only_traits_in_impl_trait_block() {
+    check(
+        r#"
+//- /main.rs crate:main deps:dep
+pub struct Bar;
+
+impl Foo$0 for Bar { }
+//- /lib.rs crate:dep
+pub trait FooTrait;
+
+pub struct FooStruct;
+"#,
+        expect![[r#"
+            tt FooTrait (use dep::FooTrait)
+        "#]],
+    );
+}

crates/ide-completion/src/tests/type_pos.rs

@@ -989,3 +989,43 @@ fn foo<'a>() { S::<'static, F$0, _, _>; }
         "#]],
     );
 }
+
+#[test]
+fn complete_traits_on_impl_trait_block() {
+    check(
+        r#"
+trait Foo {}
+
+struct Bar;
+
+impl $0 for Bar { }
+"#,
+        expect![[r#"
+            md module
+            tt Foo
+            tt Trait
+            kw crate::
+            kw self::
+        "#]],
+    );
+}
+
+#[test]
+fn complete_traits_with_path_on_impl_trait_block() {
+    check(
+        r#"
+mod outer {
+    pub trait Foo {}
+    pub struct Bar;
+    pub mod inner {
+    }
+}
+
+impl outer::$0 for Bar { }
+"#,
+        expect![[r#"
+            md inner
+            tt Foo
+        "#]],
+    );
+}