Do not talk about "trait <Foo = Bar>"

Pass in an appropriate `Option<DefId>` in more cases from hir ty lowering.

Author: estebank

compiler/rustc_hir_analysis/src/hir_ty_lowering/errors.rs

@@ -279,7 +279,13 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                     } else {
                         let mut err = self.dcx().create_err(err);
                         if suggest_constraining_type_param(
-                            tcx, generics, &mut err, &qself_str, &trait_ref, None, None,
+                            tcx,
+                            generics,
+                            &mut err,
+                            &qself_str,
+                            &trait_ref,
+                            Some(best_trait),
+                            None,
                         ) && !identically_named
                         {
                             // We suggested constraining a type parameter, but the associated item on it

compiler/rustc_middle/src/ty/diagnostics.rs

@@ -345,6 +345,7 @@ pub fn suggest_constraining_type_params<'a>(
         let mut constraint = constraints.iter().map(|&(c, _, _)| c).collect::<Vec<_>>();
         constraint.sort();
         constraint.dedup();
+        let all_known = constraints.iter().all(|&(_, def_id, _)| def_id.is_some());
         let all_stable = constraints.iter().all(|&(_, _, stable)| stable.is_empty());
         let all_unstable = constraints.iter().all(|&(_, _, stable)| !stable.is_empty());
         let post = if all_stable || all_unstable {
@@ -360,7 +361,8 @@ pub fn suggest_constraining_type_params<'a>(
             trait_names.dedup();
             let n = trait_names.len();
             let stable = if all_stable { "" } else { "unstable " };
-            format!("{stable}trait{} {}", pluralize!(n), match &trait_names[..] {
+            let trait_ = if all_known { "trait" } else { "" };
+            format!("{stable}{trait_}{} {}", pluralize!(n), match &trait_names[..] {
                 [t] => t.to_string(),
                 [ts @ .., last] => format!("{} and {last}", ts.join(", ")),
                 [] => return false,
@@ -370,7 +372,7 @@ pub fn suggest_constraining_type_params<'a>(
             let mut trait_names = constraints
                 .iter()
                 .map(|&(c, def_id, stable)| match def_id {
-                    None => format!("{stable}trait `{c}`"),
+                    None => format!("`{c}`"),
                     Some(def_id) => format!("{stable}trait `{}`", tcx.item_name(def_id)),
                 })
                 .collect::<Vec<_>>();

tests/ui/associated-types/hr-associated-type-projection-1.stderr

@@ -16,7 +16,7 @@ LL | trait UnsafeCopy<'a, T: Copy>
 LL | where
 LL |     for<'b> <Self as UnsafeCopy<'b, T>>::Item: std::ops::Deref<Target = T>,
    |                                                                ^^^^^^^^^^ required by this bound in `UnsafeCopy`
-help: consider further restricting this bound with trait `<Target = T>`
+help: consider further restricting this bound with  `<Target = T>`
    |
 LL | impl<T: Copy + std::ops::Deref<Target = T>> UnsafeCopy<'_, T> for T {
    |                               ++++++++++++

tests/ui/generic-associated-types/issue-68656-unsized-values.stderr

@@ -13,7 +13,7 @@ note: required by a bound in `UnsafeCopy::Item`
    |
 LL |     type Item<'a>: std::ops::Deref<Target = T>;
    |                                    ^^^^^^^^^^ required by this bound in `UnsafeCopy::Item`
-help: consider further restricting this bound with trait `<Target = T>`
+help: consider further restricting this bound with  `<Target = T>`
    |
 LL | impl<T: Copy + std::ops::Deref<Target = T>> UnsafeCopy<T> for T {
    |                               ++++++++++++

tests/ui/generic-associated-types/missing-bounds.stderr

@@ -35,7 +35,7 @@ note: tuple struct defined here
    |
 LL | struct A<B>(B);
    |        ^
-help: consider further restricting this bound with trait `<Output = B>`
+help: consider further restricting this bound with  `<Output = B>`
    |
 LL | impl<B> Add for A<B> where B: Add<Output = B> {
    |                                  ++++++++++++
@@ -58,7 +58,7 @@ note: tuple struct defined here
    |
 LL | struct C<B>(B);
    |        ^
-help: consider further restricting this bound with trait `<Output = B>`
+help: consider further restricting this bound with  `<Output = B>`
    |
 LL | impl<B: Add<Output = B>> Add for C<B> {
    |            ++++++++++++
@@ -94,7 +94,7 @@ note: tuple struct defined here
    |
 LL | struct E<B>(B);
    |        ^
-help: consider further restricting this bound with trait `<Output = B>`
+help: consider further restricting this bound with  `<Output = B>`
    |
 LL | impl<B: Add<Output = B>> Add for E<B> where <B as Add>::Output = B {
    |            ++++++++++++

tests/ui/suggestions/restrict-existing-type-bounds.stderr

@@ -20,7 +20,7 @@ LL |         Ok(self)
    |            this argument influences the type of `Ok`
 note: tuple variant defined here
   --> $SRC_DIR/core/src/result.rs:LL:COL
-help: consider further restricting this bound with trait `<Output = T>`
+help: consider further restricting this bound with  `<Output = T>`
    |
 LL | impl<T: TryAdd<Output = T>> TryAdd for Option<T> {
    |               ++++++++++++
@@ -47,7 +47,7 @@ LL |         Ok(self)
    |            this argument influences the type of `Ok`
 note: tuple variant defined here
   --> $SRC_DIR/core/src/result.rs:LL:COL
-help: consider further restricting this bound with trait `, Output = T`
+help: consider further restricting this bound with  `, Output = T`
    |
 LL | impl<T: TryAdd<Error = X, Output = T>> TryAdd for Other<T> {
    |                         ++++++++++++

tests/ui/trait-bounds/restrict-assoc-type-of-generic-bound.stderr

@@ -11,7 +11,7 @@ LL |     return a.bar();
    = note: expected type parameter `B`
              found associated type `<A as MyTrait>::T`
    = note: the caller chooses a type for `B` which can be different from `<A as MyTrait>::T`
-help: consider further restricting this bound with trait `<T = B>`
+help: consider further restricting this bound with  `<T = B>`
    |
 LL | pub fn foo<A: MyTrait<T = B>, B>(a: A) -> B {
    |                      +++++++

tests/ui/traits/copy-is-not-modulo-regions.not_static.stderr

@@ -12,7 +12,7 @@ note: the `Copy` impl for `Foo<'any>` requires that `'any: 'static`
    |
 LL | struct Bar<'lt>(Foo<'lt>);
    |                 ^^^^^^^^
-help: consider restricting type parameter `'any` with trait `'static`
+help: consider restricting type parameter `'any` with  `'static`
    |
 LL | impl<'any: 'static> Copy for Bar<'any> {}
    |          +++++++++

tests/ui/type-alias/unresolved-assoc-ty-suggest-trait.lazy.stderr

@@ -30,7 +30,7 @@ error[E0220]: associated type `Proj` not found for `T`
 LL | type ProjOf<T> = T::Proj;
    |                     ^^^^ there is an associated type `Proj` in the trait `Parametrized`
    |
-help: consider restricting type parameter `T` with trait `Parametrized</* 'a, T, N */>`
+help: consider restricting type parameter `T` with trait `Parametrized`
    |
 LL | type ProjOf<T: Parametrized</* 'a, T, N */>> = T::Proj;
    |              ++++++++++++++++++++++++++++++