Make missing impl item suggestions more obvious that they're missing

compiler/rustc_hir_analysis/src/check/mod.rs

@@ -466,10 +466,10 @@ fn suggestion_signature<'tcx>(
                 assoc,
             )
         }
-        ty::AssocKind::Type => format!("type {} = Type;", assoc.name),
+        ty::AssocKind::Type => format!("type {} = /* Type */;", assoc.name),
         ty::AssocKind::Const => {
             let ty = tcx.type_of(assoc.def_id).subst_identity();
-            let val = ty_kind_suggestion(ty).unwrap_or("value");
+            let val = ty_kind_suggestion(ty).unwrap_or("todo!()");
             format!("const {}: {} = {};", assoc.name, ty, val)
         }
     }

tests/ui/async-await/issue-74047.stderr

@@ -4,7 +4,7 @@ error[E0046]: not all trait items implemented, missing: `Error`, `try_from`
 LL | impl TryFrom<OtherStream> for MyStream {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `Error`, `try_from` in implementation
    |
-   = help: implement the missing item: `type Error = Type;`
+   = help: implement the missing item: `type Error = /* Type */;`
    = help: implement the missing item: `fn try_from(_: OtherStream) -> Result<Self, <Self as TryFrom<OtherStream>>::Error> { todo!() }`
 
 error: aborting due to previous error

tests/ui/missing/missing-items/m2.stderr

@@ -5,7 +5,7 @@ LL | impl m1::X for X {
    | ^^^^^^^^^^^^^^^^ missing `CONSTANT`, `Type`, `method`, `method2`, `method3`, `method4`, `method5` in implementation
    |
    = help: implement the missing item: `const CONSTANT: u32 = 42;`
-   = help: implement the missing item: `type Type = Type;`
+   = help: implement the missing item: `type Type = /* Type */;`
    = help: implement the missing item: `fn method(&self, _: String) -> <Self as m1::X>::Type { todo!() }`
    = help: implement the missing item: `fn method2(self: Box<Self>, _: String) -> <Self as m1::X>::Type { todo!() }`
    = help: implement the missing item: `fn method3(_: &Self, _: String) -> <Self as m1::X>::Type { todo!() }`

tests/ui/span/issue-23729.stderr

@@ -4,7 +4,7 @@ error[E0046]: not all trait items implemented, missing: `Item`
 LL |         impl Iterator for Recurrence {
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `Item` in implementation
    |
-   = help: implement the missing item: `type Item = Type;`
+   = help: implement the missing item: `type Item = /* Type */;`
 
 error: aborting due to previous error
 

tests/ui/span/issue-23827.stderr

@@ -4,7 +4,7 @@ error[E0046]: not all trait items implemented, missing: `Output`
 LL | impl<C: Component> FnOnce<(C,)> for Prototype {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `Output` in implementation
    |
-   = help: implement the missing item: `type Output = Type;`
+   = help: implement the missing item: `type Output = /* Type */;`
 
 error: aborting due to previous error
 

tests/ui/span/issue-24356.stderr

@@ -4,7 +4,7 @@ error[E0046]: not all trait items implemented, missing: `Target`
 LL |         impl Deref for Thing {
    |         ^^^^^^^^^^^^^^^^^^^^ missing `Target` in implementation
    |
-   = help: implement the missing item: `type Target = Type;`
+   = help: implement the missing item: `type Target = /* Type */;`
 
 error: aborting due to previous error
 

tests/ui/suggestions/auxiliary/missing-assoc-fn-applicable-suggestions.rs

@@ -0,0 +1,16 @@
+pub trait TraitB {
+    type Item;
+}
+
+pub trait TraitA<A> {
+    type Type;
+
+    fn bar<T>(_: T) -> Self;
+
+    fn baz<T>(_: T) -> Self
+    where
+        T: TraitB,
+        <T as TraitB>::Item: Copy;
+
+    const A: usize;
+}

tests/ui/suggestions/missing-assoc-fn-applicable-suggestions.fixed

@@ -1,21 +0,0 @@
-// run-rustfix
-trait TraitB {
-    type Item;
-}
-
-trait TraitA<A> {
-    type Type;
-    fn bar<T>(_: T) -> Self;
-    fn baz<T>(_: T) -> Self where T: TraitB, <T as TraitB>::Item: Copy;
-}
-
-struct S;
-struct Type;
-
-impl TraitA<()> for S { //~ ERROR not all trait items implemented
-fn baz<T>(_: T) -> Self where T: TraitB, <T as TraitB>::Item: Copy { todo!() }
-fn bar<T>(_: T) -> Self { todo!() }
-type Type = Type;
-}
-
-fn main() {}

tests/ui/suggestions/missing-assoc-fn-applicable-suggestions.rs

@@ -1,18 +1,15 @@
-// run-rustfix
+// aux-build:missing-assoc-fn-applicable-suggestions.rs
-trait TraitB {
-    type Item;
-}
 
-trait TraitA<A> {
+extern crate missing_assoc_fn_applicable_suggestions;
-    type Type;
+use missing_assoc_fn_applicable_suggestions::TraitA;
-    fn bar<T>(_: T) -> Self;
-    fn baz<T>(_: T) -> Self where T: TraitB, <T as TraitB>::Item: Copy;
-}
 
 struct S;
-struct Type;
+impl TraitA<()> for S {
-
+    //~^ ERROR not all trait items implemented
-impl TraitA<()> for S { //~ ERROR not all trait items implemented
 }
+//~^ HELP implement the missing item: `type Type = /* Type */;`
+//~| HELP implement the missing item: `fn bar<T>(_: T) -> Self { todo!() }`
+//~| HELP implement the missing item: `fn baz<T>(_: T) -> Self where T: TraitB, <T as TraitB>::Item: Copy { todo!() }`
+//~| HELP implement the missing item: `const A: usize = 42;`
 
 fn main() {}

tests/ui/suggestions/missing-assoc-fn-applicable-suggestions.stderr

@@ -1,15 +1,13 @@
-error[E0046]: not all trait items implemented, missing: `Type`, `bar`, `baz`
+error[E0046]: not all trait items implemented, missing: `Type`, `bar`, `baz`, `A`
-  --> $DIR/missing-assoc-fn-applicable-suggestions.rs:15:1
+  --> $DIR/missing-assoc-fn-applicable-suggestions.rs:7:1
    |
-LL |     type Type;
+LL | impl TraitA<()> for S { 
-   |     --------- `Type` from trait
+   | ^^^^^^^^^^^^^^^^^^^^^ missing `Type`, `bar`, `baz`, `A` in implementation
-LL |     fn bar<T>(_: T) -> Self;
+   |
-   |     ------------------------ `bar` from trait
+   = help: implement the missing item: `type Type = /* Type */;`
-LL |     fn baz<T>(_: T) -> Self where T: TraitB, <T as TraitB>::Item: Copy;
+   = help: implement the missing item: `fn bar<T>(_: T) -> Self { todo!() }`
-   |     ------------------------------------------------------------------- `baz` from trait
+   = help: implement the missing item: `fn baz<T>(_: T) -> Self where T: TraitB, <T as TraitB>::Item: Copy { todo!() }`
-...
+   = help: implement the missing item: `const A: usize = 42;`
-LL | impl TraitA<()> for S {
-   | ^^^^^^^^^^^^^^^^^^^^^ missing `Type`, `bar`, `baz` in implementation
 
 error: aborting due to previous error