Substitute missing trait items suggestion correctly

compiler/rustc_hir_analysis/src/check/check.rs

@@ -863,7 +863,7 @@ fn check_impl_items_against_trait<'tcx>(
         if !missing_items.is_empty() {
             let full_impl_span =
                 tcx.hir().span_with_body(tcx.hir().local_def_id_to_hir_id(impl_id));
-            missing_items_err(tcx, tcx.def_span(impl_id), &missing_items, full_impl_span);
+            missing_items_err(tcx, impl_id, &missing_items, full_impl_span);
         }
 
         if let Some(missing_items) = must_implement_one_of {

compiler/rustc_hir_analysis/src/check/mod.rs

@@ -198,7 +198,7 @@ fn report_forbidden_specialization(tcx: TyCtxt<'_>, impl_item: DefId, parent_imp
 
 fn missing_items_err(
     tcx: TyCtxt<'_>,
-    impl_span: Span,
+    impl_def_id: LocalDefId,
     missing_items: &[ty::AssocItem],
     full_impl_span: Span,
 ) {
@@ -211,6 +211,7 @@ fn missing_items_err(
         .collect::<Vec<_>>()
         .join("`, `");
 
+    let impl_span = tcx.def_span(impl_def_id);
     let mut err = struct_span_err!(
         tcx.sess,
         impl_span,
@@ -229,7 +230,11 @@ fn missing_items_err(
         tcx.sess.source_map().indentation_before(sugg_sp).unwrap_or_else(|| String::new());
 
     for &trait_item in missing_items {
-        let snippet = suggestion_signature(trait_item, tcx);
+        let snippet = suggestion_signature(
+            tcx,
+            trait_item,
+            tcx.impl_trait_ref(impl_def_id).unwrap().subst_identity(),
+        );
         let code = format!("{}{}\n{}", padding, snippet, padding);
         let msg = format!("implement the missing item: `{snippet}`");
         let appl = Applicability::HasPlaceholders;
@@ -301,11 +306,11 @@ fn default_body_is_unstable(
 /// Re-sugar `ty::GenericPredicates` in a way suitable to be used in structured suggestions.
 fn bounds_from_generic_predicates<'tcx>(
     tcx: TyCtxt<'tcx>,
-    predicates: ty::GenericPredicates<'tcx>,
+    predicates: impl IntoIterator<Item = (ty::Predicate<'tcx>, Span)>,
 ) -> (String, String) {
     let mut types: FxHashMap<Ty<'tcx>, Vec<DefId>> = FxHashMap::default();
     let mut projections = vec![];
-    for (predicate, _) in predicates.predicates {
+    for (predicate, _) in predicates {
         debug!("predicate {:?}", predicate);
         let bound_predicate = predicate.kind();
         match bound_predicate.skip_binder() {
@@ -367,7 +372,7 @@ fn fn_sig_suggestion<'tcx>(
     tcx: TyCtxt<'tcx>,
     sig: ty::FnSig<'tcx>,
     ident: Ident,
-    predicates: ty::GenericPredicates<'tcx>,
+    predicates: impl IntoIterator<Item = (ty::Predicate<'tcx>, Span)>,
     assoc: ty::AssocItem,
 ) -> String {
     let args = sig
@@ -436,7 +441,17 @@ pub fn ty_kind_suggestion(ty: Ty<'_>) -> Option<&'static str> {
 /// Return placeholder code for the given associated item.
 /// Similar to `ty::AssocItem::suggestion`, but appropriate for use as the code snippet of a
 /// structured suggestion.
-fn suggestion_signature(assoc: ty::AssocItem, tcx: TyCtxt<'_>) -> String {
+fn suggestion_signature<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    assoc: ty::AssocItem,
+    impl_trait_ref: ty::TraitRef<'tcx>,
+) -> String {
+    let substs = ty::InternalSubsts::identity_for_item(tcx, assoc.def_id).rebase_onto(
+        tcx,
+        assoc.container_id(tcx),
+        impl_trait_ref.with_self_ty(tcx, tcx.types.self_param).substs,
+    );
+
     match assoc.kind {
         ty::AssocKind::Fn => {
             // We skip the binder here because the binder would deanonymize all
@@ -445,16 +460,22 @@ fn suggestion_signature(assoc: ty::AssocItem, tcx: TyCtxt<'_>) -> String {
             // regions just fine, showing `fn(&MyType)`.
             fn_sig_suggestion(
                 tcx,
-                tcx.fn_sig(assoc.def_id).subst_identity().skip_binder(),
+                tcx.fn_sig(assoc.def_id).subst(tcx, substs).skip_binder(),
                 assoc.ident(tcx),
-                tcx.predicates_of(assoc.def_id),
+                tcx.predicates_of(assoc.def_id).instantiate_own(tcx, substs),
                 assoc,
             )
         }
-        ty::AssocKind::Type => format!("type {} = Type;", assoc.name),
+        ty::AssocKind::Type => {
+            let (generics, where_clauses) = bounds_from_generic_predicates(
+                tcx,
+                tcx.predicates_of(assoc.def_id).instantiate_own(tcx, substs),
+            );
+            format!("type {}{generics} = /* Type */{where_clauses};", 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

@@ -4,8 +4,8 @@ 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: `fn try_from(_: T) -> Result<Self, <Self as TryFrom<T>>::Error> { todo!() }`
+   = 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/generic-associated-types/auxiliary/missing-item-sugg.rs

@@ -0,0 +1,5 @@
+pub trait Foo {
+    type Gat<T>
+    where
+        T: std::fmt::Display;
+}

tests/ui/generic-associated-types/missing-item-sugg.rs

@@ -0,0 +1,11 @@
+// aux-build:missing-item-sugg.rs
+
+extern crate missing_item_sugg;
+
+struct Local;
+impl missing_item_sugg::Foo for Local {
+    //~^ ERROR not all trait items implemented, missing: `Gat`
+}
+//~^ HELP implement the missing item: `type Gat<T> = /* Type */ where T: std::fmt::Display;`
+
+fn main() {}

tests/ui/generic-associated-types/missing-item-sugg.stderr

@@ -0,0 +1,11 @@
+error[E0046]: not all trait items implemented, missing: `Gat`
+  --> $DIR/missing-item-sugg.rs:6:1
+   |
+LL | impl missing_item_sugg::Foo for Local {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `Gat` in implementation
+   |
+   = help: implement the missing item: `type Gat<T> = /* Type */ where T: std::fmt::Display;`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0046`.

tests/ui/issues/issue-3344.stderr

@@ -4,7 +4,7 @@ error[E0046]: not all trait items implemented, missing: `partial_cmp`
 LL | impl PartialOrd for Thing {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^ missing `partial_cmp` in implementation
    |
-   = help: implement the missing item: `fn partial_cmp(&self, _: &Rhs) -> Option<std::cmp::Ordering> { todo!() }`
+   = help: implement the missing item: `fn partial_cmp(&self, _: &Thing) -> Option<std::cmp::Ordering> { 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.rs

@@ -1,18 +1,15 @@
-// run-rustfix
-trait TraitB {
-    type Item;
-}
+// aux-build:missing-assoc-fn-applicable-suggestions.rs
 
-trait TraitA<A> {
-    type Type;
-    fn bar<T>(_: T) -> Self;
-    fn baz<T>(_: T) -> Self where T: TraitB, <T as TraitB>::Item: Copy;
-}
+extern crate missing_assoc_fn_applicable_suggestions;
+use missing_assoc_fn_applicable_suggestions::TraitA;
 
 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`
-  --> $DIR/missing-assoc-fn-applicable-suggestions.rs:15:1
+error[E0046]: not all trait items implemented, missing: `Type`, `bar`, `baz`, `A`
+  --> $DIR/missing-assoc-fn-applicable-suggestions.rs:7:1
    |
-LL |     type Type;
-   |     --------- `Type` from trait
-LL |     fn bar<T>(_: T) -> Self;
-   |     ------------------------ `bar` from trait
-LL |     fn baz<T>(_: T) -> Self where T: TraitB, <T as TraitB>::Item: Copy;
-   |     ------------------------------------------------------------------- `baz` from trait
-...
 LL | impl TraitA<()> for S {
-   | ^^^^^^^^^^^^^^^^^^^^^ missing `Type`, `bar`, `baz` in implementation
+   | ^^^^^^^^^^^^^^^^^^^^^ missing `Type`, `bar`, `baz`, `A` in implementation
+   |
+   = 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;`
 
 error: aborting due to previous error
 

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

@@ -28,7 +28,7 @@ error[E0046]: not all trait items implemented, missing: `from_iter`
 LL | impl FromIterator<()> for X {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `from_iter` in implementation
    |
-   = help: implement the missing item: `fn from_iter<T>(_: T) -> Self where T: IntoIterator, std::iter::IntoIterator::Item = A { todo!() }`
+   = help: implement the missing item: `fn from_iter<T>(_: T) -> Self where T: IntoIterator, std::iter::IntoIterator::Item = () { todo!() }`
 
 error: aborting due to 3 previous errors