Rollup merge of #110555 - compiler-errors:subst-missing-trait-items, r=cjgillot

Substitute missing trait items suggestion correctly

Properly substitute missing item suggestions, so that when they reference generics from their parent trait they actually have the right time for the impl.

Also, some other minor tweaks like using `/* Type */` to signify a GAT's type is actually missing, and fixing generic arg suggestions for GATs in general.

16 files changed, 100 insertions, 62 deletions

diff --git a/compiler/rustc_hir_analysis/src/check/check.rs b/compiler/rustc_hir_analysis/src/check/check.rs
index 0c54fd70c9b..51ec5dd7a28 100644
--- a/compiler/rustc_hir_analysis/src/check/check.rs
+++ b/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 {
diff --git a/compiler/rustc_hir_analysis/src/check/mod.rs b/compiler/rustc_hir_analysis/src/check/mod.rs
index 8fe4c44fca4..4b3f3cf169d 100644
--- a/compiler/rustc_hir_analysis/src/check/mod.rs
+++ b/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)
         }
     }
diff --git a/tests/ui/async-await/issue-74047.stderr b/tests/ui/async-await/issue-74047.stderr
index 28174825d8b..6bdb9ded482 100644
--- a/tests/ui/async-await/issue-74047.stderr
+++ b/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
 
diff --git a/tests/ui/generic-associated-types/auxiliary/missing-item-sugg.rs b/tests/ui/generic-associated-types/auxiliary/missing-item-sugg.rs
new file mode 100644
index 00000000000..5b10aab4b3f
--- /dev/null
+++ b/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;
+}
diff --git a/tests/ui/generic-associated-types/missing-item-sugg.rs b/tests/ui/generic-associated-types/missing-item-sugg.rs
new file mode 100644
index 00000000000..35d573d8188
--- /dev/null
+++ b/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() {}
diff --git a/tests/ui/generic-associated-types/missing-item-sugg.stderr b/tests/ui/generic-associated-types/missing-item-sugg.stderr
new file mode 100644
index 00000000000..378115f6d38
--- /dev/null
+++ b/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`.
diff --git a/tests/ui/issues/issue-3344.stderr b/tests/ui/issues/issue-3344.stderr
index 11d5999672e..e849f5d0490 100644
--- a/tests/ui/issues/issue-3344.stderr
+++ b/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
 
diff --git a/tests/ui/missing/missing-items/m2.stderr b/tests/ui/missing/missing-items/m2.stderr
index d18fb443aa4..835c9b2aa48 100644
--- a/tests/ui/missing/missing-items/m2.stderr
+++ b/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!() }`
diff --git a/tests/ui/span/issue-23729.stderr b/tests/ui/span/issue-23729.stderr
index f88ce6c88db..cd854e61f2f 100644
--- a/tests/ui/span/issue-23729.stderr
+++ b/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
 
diff --git a/tests/ui/span/issue-23827.stderr b/tests/ui/span/issue-23827.stderr
index 46a820f1b76..83a9e8c9b98 100644
--- a/tests/ui/span/issue-23827.stderr
+++ b/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
 
diff --git a/tests/ui/span/issue-24356.stderr b/tests/ui/span/issue-24356.stderr
index a1f9b255020..cf666e8b4a7 100644
--- a/tests/ui/span/issue-24356.stderr
+++ b/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
 
diff --git a/tests/ui/suggestions/auxiliary/missing-assoc-fn-applicable-suggestions.rs b/tests/ui/suggestions/auxiliary/missing-assoc-fn-applicable-suggestions.rs
new file mode 100644
index 00000000000..b026035a6a1
--- /dev/null
+++ b/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;
+}
diff --git a/tests/ui/suggestions/missing-assoc-fn-applicable-suggestions.fixed b/tests/ui/suggestions/missing-assoc-fn-applicable-suggestions.fixed
deleted file mode 100644
index a0cb39a3f8a..00000000000
--- a/tests/ui/suggestions/missing-assoc-fn-applicable-suggestions.fixed
+++ /dev/null
@@ -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() {}
diff --git a/tests/ui/suggestions/missing-assoc-fn-applicable-suggestions.rs b/tests/ui/suggestions/missing-assoc-fn-applicable-suggestions.rs
index c80ede1b2be..11e0c9a3a72 100644
--- a/tests/ui/suggestions/missing-assoc-fn-applicable-suggestions.rs
+++ b/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() {}
diff --git a/tests/ui/suggestions/missing-assoc-fn-applicable-suggestions.stderr b/tests/ui/suggestions/missing-assoc-fn-applicable-suggestions.stderr
index 4c75fbe4c78..4c2d2776d3d 100644
--- a/tests/ui/suggestions/missing-assoc-fn-applicable-suggestions.stderr
+++ b/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
 
diff --git a/tests/ui/suggestions/missing-assoc-fn.stderr b/tests/ui/suggestions/missing-assoc-fn.stderr
index 136ec2152e0..77fa9562878 100644
--- a/tests/ui/suggestions/missing-assoc-fn.stderr
+++ b/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