E0220: only suggests associated types if there's only one candidate

Author: ShE3py

compiler/rustc_hir_analysis/src/astconv/errors.rs

@@ -201,33 +201,27 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
  }
  }
 
- // If we still couldn't find any associated type, just list them all.
-
- if all_candidate_names.is_empty() {
- err.help(format!(
- "`{ty_param_name}` has no associated type, try removing `{assoc_name}`"
- ));
- return err.emit();
- }
-
- let msg = if all_candidate_names.len() > 1 {
- format!("`{ty_param_name}` has the following associated types")
- } else {
- format!("`{ty_param_name}` has the following associated type")
- };
+ // If we still couldn't find any associated type, and only one associated type exists,
+ // suggests using it.
+
+ if all_candidate_names.len() == 1 {
+ // this should still compile, except on `#![feature(associated_type_defaults)]`
+ // where it could suggests `type A = Self::A`, thus recursing infinitely
+ let applicability = if self.tcx().features().associated_type_defaults {
+ Applicability::Unspecified
+ } else {
+ Applicability::MaybeIncorrect
+ };
 
- let applicability = if self.tcx().features().associated_type_defaults {
- Applicability::Unspecified // `type A = Self::B` would suggest `type A = Self::A`
+ err.span_suggestion(
+ assoc_name.span,
+ format!("`{ty_param_name}` has the following associated type"),
+ all_candidate_names.first().unwrap().to_string(),
+ applicability,
+ );
  } else {
- Applicability::MaybeIncorrect
- };
-
- err.span_suggestions(
- assoc_name.span,
- msg,
- all_candidate_names.iter().map(|symbol| symbol.to_string()),
- applicability,
- );
+ err.span_label(assoc_name.span, format!("associated type `{assoc_name}` not found"));
+ }
 
  err.emit()
  }

tests/ui/associated-consts/assoc-const-eq-missing.stderr

@@ -2,25 +2,19 @@ error[E0220]: associated type `Z` not found for `Foo`
  --> $DIR/assoc-const-eq-missing.rs:15:16
  |
 LL | fn foo1<F: Foo<Z=3>>() {}
- | ^
- |
- = help: `Foo` has no associated type, try removing `Z`
+ | ^ associated type `Z` not found
 
 error[E0220]: associated type `Z` not found for `Foo`
  --> $DIR/assoc-const-eq-missing.rs:17:16
  |
 LL | fn foo2<F: Foo<Z=usize>>() {}
- | ^
- |
- = help: `Foo` has no associated type, try removing `Z`
+ | ^ associated type `Z` not found
 
 error[E0220]: associated type `Z` not found for `Foo`
  --> $DIR/assoc-const-eq-missing.rs:19:16
  |
 LL | fn foo3<F: Foo<Z=5>>() {}
- | ^
- |
- = help: `Foo` has no associated type, try removing `Z`
+ | ^ associated type `Z` not found
 
 error: aborting due to 3 previous errors
 

tests/ui/associated-type-bounds/missing-trait-bound-for-assoc-fails.stderr

@@ -8,9 +8,7 @@ error[E0220]: associated type `Item` not found for `M`
  --> $DIR/missing-trait-bound-for-assoc-fails.rs:4:8
  |
 LL | M::Item: Temp,
- | ^^^^
- |
- = help: `M` has no associated type, try removing `Item`
+ | ^^^^ associated type `Item` not found
 
 error: aborting due to 2 previous errors
 

tests/ui/associated-types/associated-types-path-1.stderr

@@ -2,9 +2,7 @@ error[E0220]: associated type `A` not found for `T`
  --> $DIR/associated-types-path-1.rs:10:26
  |
 LL | pub fn f1<T>(a: T, x: T::A) {}
- | ^
- |
- = help: `T` has no associated type, try removing `A`
+ | ^ associated type `A` not found
 
 error[E0221]: ambiguous associated type `A` in bounds of `T`
  --> $DIR/associated-types-path-1.rs:11:34

tests/ui/feature-gates/feature-gate-return_type_notation.cfg.stderr

@@ -19,9 +19,7 @@ error[E0220]: associated type `m` not found for `Trait`
  --> $DIR/feature-gate-return_type_notation.rs:14:17
  |
 LL | fn foo<T: Trait<m(): Send>>() {}
- | ^
- |
- = help: `Trait` has no associated type, try removing `m`
+ | ^ associated type `m` not found
 
 error: aborting due to 3 previous errors
 

tests/ui/feature-gates/feature-gate-return_type_notation.cfg_current.stderr

@@ -19,9 +19,7 @@ error[E0220]: associated type `m` not found for `Trait`
  --> $DIR/feature-gate-return_type_notation.rs:17:17
  |
 LL | fn foo<T: Trait<m(): Send>>() {}
- | ^
- |
- = help: `Trait` has no associated type, try removing `m`
+ | ^ associated type `m` not found
 
 error: aborting due to 3 previous errors
 

tests/ui/feature-gates/feature-gate-return_type_notation.cfg_next.stderr

@@ -19,9 +19,7 @@ error[E0220]: associated type `m` not found for `Trait`
  --> $DIR/feature-gate-return_type_notation.rs:17:17
  |
 LL | fn foo<T: Trait<m(): Send>>() {}
- | ^
- |
- = help: `Trait` has no associated type, try removing `m`
+ | ^ associated type `m` not found
 
 error: aborting due to 3 previous errors