Auto merge of #118668 - fmease:resolve-assoc-item-bindings-by-namespace, r=compiler-errors

Resolve associated item bindings by namespace

This is the 3rd commit split off from #118360 with tests reblessed (they no longer contain duplicated diags which were caused by 4c0addc80af4666f26d7ad51fe34a0e2dd0b8b74) & slightly adapted (removed supertraits from a UI test, cc #118040).

> * Resolve all assoc item bindings (type, const, fn (feature `return_type_notation`)) by namespace instead of trying to resolve a type first (in the non-RTN case) and falling back to consts afterwards. This is consistent with RTN. E.g., for `Tr<K = {…}>` we now always try to look up assoc consts (this extends to supertrait bounds). This gets rid of assoc tys shadowing assoc consts in assoc item bindings which is undesirable & inconsistent (types and consts live in different namespaces after all)
> * Consolidate the resolution of assoc {ty, const} bindings and RTN (dedup, better diags for RTN)
> * Fix assoc consts being labeled as assoc *types* in several diagnostics
> * Make a bunch of diagnostics translatable

Fixes #112560 (error → pass).

As discussed
r? `@compiler-errors`

---

**Addendum**: What I call “associated item bindings” are commonly referred to as “type bindings” for historical reasons. Nowadays, “type bindings” include assoc type bindings, assoc const bindings and RTN (return type notation) which is why I prefer not to use this outdated term.

22 files changed, 199 insertions, 81 deletions

diff --git a/tests/ui/associated-consts/assoc-const-eq-ambiguity.rs b/tests/ui/associated-consts/assoc-const-eq-ambiguity.rs
new file mode 100644
index 00000000000..ac085864ff0
--- /dev/null
+++ b/tests/ui/associated-consts/assoc-const-eq-ambiguity.rs
@@ -0,0 +1,19 @@
+// We used to say "ambiguous associated type" on ambiguous associated consts.
+// Ensure that we now use the correct label.
+
+#![feature(associated_const_equality)]
+
+trait Trait0: Parent0<i32> + Parent0<u32> {}
+trait Parent0<T> { const K: (); }
+
+fn take0(_: impl Trait0<K = { () }>) {}
+//~^ ERROR ambiguous associated constant `K` in bounds of `Trait0`
+
+trait Trait1: Parent1 + Parent2 {}
+trait Parent1 { const C: i32; }
+trait Parent2 { const C: &'static str; }
+
+fn take1(_: impl Trait1<C = "?">) {}
+//~^ ERROR ambiguous associated constant `C` in bounds of `Trait1`
+
+fn main() {}
diff --git a/tests/ui/associated-consts/assoc-const-eq-ambiguity.stderr b/tests/ui/associated-consts/assoc-const-eq-ambiguity.stderr
new file mode 100644
index 00000000000..ba3a8701316
--- /dev/null
+++ b/tests/ui/associated-consts/assoc-const-eq-ambiguity.stderr
@@ -0,0 +1,38 @@
+error[E0222]: ambiguous associated constant `K` in bounds of `Trait0`
+  --> $DIR/assoc-const-eq-ambiguity.rs:9:25
+   |
+LL | trait Parent0<T> { const K: (); }
+   |                    -----------
+   |                    |
+   |                    ambiguous `K` from `Parent0<u32>`
+   |                    ambiguous `K` from `Parent0<i32>`
+LL |
+LL | fn take0(_: impl Trait0<K = { () }>) {}
+   |                         ^^^^^^^^^^ ambiguous associated constant `K`
+   |
+   = help: consider introducing a new type parameter `T` and adding `where` constraints:
+               where
+                   T: Trait0,
+                   T: Parent0<u32>::K = { () },
+                   T: Parent0<i32>::K = { () }
+
+error[E0222]: ambiguous associated constant `C` in bounds of `Trait1`
+  --> $DIR/assoc-const-eq-ambiguity.rs:16:25
+   |
+LL | trait Parent1 { const C: i32; }
+   |                 ------------ ambiguous `C` from `Parent1`
+LL | trait Parent2 { const C: &'static str; }
+   |                 --------------------- ambiguous `C` from `Parent2`
+LL |
+LL | fn take1(_: impl Trait1<C = "?">) {}
+   |                         ^^^^^^^ ambiguous associated constant `C`
+   |
+   = help: consider introducing a new type parameter `T` and adding `where` constraints:
+               where
+                   T: Trait1,
+                   T: Parent2::C = "?",
+                   T: Parent1::C = "?"
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0222`.
diff --git a/tests/ui/associated-consts/assoc-const-eq-missing.rs b/tests/ui/associated-consts/assoc-const-eq-missing.rs
index 5e029a12df2..f384927e4a3 100644
--- a/tests/ui/associated-consts/assoc-const-eq-missing.rs
+++ b/tests/ui/associated-consts/assoc-const-eq-missing.rs
@@ -11,13 +11,12 @@ impl Foo for Bar {
   const N: usize = 3;
 }
 
-
-fn foo1<F: Foo<Z=3>>() {}
-//~^ ERROR associated type
-fn foo2<F: Foo<Z=usize>>() {}
-//~^ ERROR associated type
-fn foo3<F: Foo<Z=5>>() {}
-//~^ ERROR associated type
+fn foo1<F: Foo<Z = 3>>() {}
+//~^ ERROR associated constant `Z` not found for `Foo`
+fn foo2<F: Foo<Z = usize>>() {}
+//~^ ERROR associated type `Z` not found for `Foo`
+fn foo3<F: Foo<Z = 5>>() {}
+//~^ ERROR associated constant `Z` not found for `Foo`
 
 fn main() {
   foo1::<Bar>();
diff --git a/tests/ui/associated-consts/assoc-const-eq-missing.stderr b/tests/ui/associated-consts/assoc-const-eq-missing.stderr
index b4bd6456c85..318c85dcfd6 100644
--- a/tests/ui/associated-consts/assoc-const-eq-missing.stderr
+++ b/tests/ui/associated-consts/assoc-const-eq-missing.stderr
@@ -1,20 +1,20 @@
-error[E0220]: associated type `Z` not found for `Foo`
-  --> $DIR/assoc-const-eq-missing.rs:15:16
+error[E0220]: associated constant `Z` not found for `Foo`
+  --> $DIR/assoc-const-eq-missing.rs:14:16
    |
-LL | fn foo1<F: Foo<Z=3>>() {}
-   |                ^ associated type `Z` not found
+LL | fn foo1<F: Foo<Z = 3>>() {}
+   |                ^ help: there is an associated constant with a similar name: `N`
 
 error[E0220]: associated type `Z` not found for `Foo`
-  --> $DIR/assoc-const-eq-missing.rs:17:16
+  --> $DIR/assoc-const-eq-missing.rs:16:16
    |
-LL | fn foo2<F: Foo<Z=usize>>() {}
+LL | fn foo2<F: Foo<Z = usize>>() {}
    |                ^ associated type `Z` not found
 
-error[E0220]: associated type `Z` not found for `Foo`
-  --> $DIR/assoc-const-eq-missing.rs:19:16
+error[E0220]: associated constant `Z` not found for `Foo`
+  --> $DIR/assoc-const-eq-missing.rs:18:16
    |
-LL | fn foo3<F: Foo<Z=5>>() {}
-   |                ^ associated type `Z` not found
+LL | fn foo3<F: Foo<Z = 5>>() {}
+   |                ^ help: there is an associated constant with a similar name: `N`
 
 error: aborting due to 3 previous errors
 
diff --git a/tests/ui/associated-consts/assoc-const-eq-ty-alias-noninteracting.rs b/tests/ui/associated-consts/assoc-const-eq-ty-alias-noninteracting.rs
new file mode 100644
index 00000000000..de9008bfcf9
--- /dev/null
+++ b/tests/ui/associated-consts/assoc-const-eq-ty-alias-noninteracting.rs
@@ -0,0 +1,21 @@
+// Regression test for issue #112560.
+// Respect the fact that (associated) types and constants live in different namespaces and
+// therefore equality bounds involving identically named associated items don't conflict if
+// their kind (type vs. const) differs.
+
+// FIXME(fmease): Extend this test to cover supertraits again
+// once #118040 is fixed. See initial version of PR #118360.
+
+// check-pass
+
+#![feature(associated_const_equality)]
+
+trait Trait {
+    type N;
+
+    const N: usize;
+}
+
+fn take(_: impl Trait<N = 0, N = ()>) {}
+
+fn main() {}
diff --git a/tests/ui/associated-consts/assoc-const-ty-mismatch.rs b/tests/ui/associated-consts/assoc-const-ty-mismatch.rs
index c5d78469e95..7211637659b 100644
--- a/tests/ui/associated-consts/assoc-const-ty-mismatch.rs
+++ b/tests/ui/associated-consts/assoc-const-ty-mismatch.rs
@@ -2,30 +2,30 @@
 #![allow(unused)]
 
 pub trait Foo {
-  const N: usize;
+    const N: usize;
 }
 
 pub trait FooTy {
-  type T;
+    type T;
 }
 
 pub struct Bar;
 
 impl Foo for Bar {
-  const N: usize = 3;
+    const N: usize = 3;
 }
 
 impl FooTy for Bar {
-  type T = usize;
+    type T = usize;
 }
 
 
-fn foo<F: Foo<N=usize>>() {}
-//~^ ERROR expected associated constant bound, found type
-fn foo2<F: FooTy<T=3usize>>() {}
-//~^ ERROR expected associated type bound, found constant
+fn foo<F: Foo<N = usize>>() {}
+//~^ ERROR expected constant, found type
+fn foo2<F: FooTy<T = 3usize>>() {}
+//~^ ERROR expected type, found constant
 
 fn main() {
-  foo::<Bar>();
-  foo2::<Bar>();
+    foo::<Bar>();
+    foo2::<Bar>();
 }
diff --git a/tests/ui/associated-consts/assoc-const-ty-mismatch.stderr b/tests/ui/associated-consts/assoc-const-ty-mismatch.stderr
index 11198729e38..b844cfc4ae4 100644
--- a/tests/ui/associated-consts/assoc-const-ty-mismatch.stderr
+++ b/tests/ui/associated-consts/assoc-const-ty-mismatch.stderr
@@ -1,26 +1,30 @@
-error: expected associated constant bound, found type
-  --> $DIR/assoc-const-ty-mismatch.rs:23:15
+error: expected constant, found type
+  --> $DIR/assoc-const-ty-mismatch.rs:23:19
    |
-LL | fn foo<F: Foo<N=usize>>() {}
-   |               ^^^^^^^
+LL | fn foo<F: Foo<N = usize>>() {}
+   |               -   ^^^^^ unexpected type
+   |               |
+   |               expected a constant because of this associated constant
    |
-note: associated constant defined here
-  --> $DIR/assoc-const-ty-mismatch.rs:5:3
+note: the associated constant is defined here
+  --> $DIR/assoc-const-ty-mismatch.rs:5:5
    |
-LL |   const N: usize;
-   |   ^^^^^^^^^^^^^^
+LL |     const N: usize;
+   |     ^^^^^^^^^^^^^^
 
-error: expected associated type bound, found constant
-  --> $DIR/assoc-const-ty-mismatch.rs:25:18
+error: expected type, found constant
+  --> $DIR/assoc-const-ty-mismatch.rs:25:22
    |
-LL | fn foo2<F: FooTy<T=3usize>>() {}
-   |                  ^^^^^^^^
+LL | fn foo2<F: FooTy<T = 3usize>>() {}
+   |                  -   ^^^^^^ unexpected constant
+   |                  |
+   |                  expected a type because of this associated type
    |
-note: associated type defined here
-  --> $DIR/assoc-const-ty-mismatch.rs:9:3
+note: the associated type is defined here
+  --> $DIR/assoc-const-ty-mismatch.rs:9:5
    |
-LL |   type T;
-   |   ^^^^^^
+LL |     type T;
+   |     ^^^^^^
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/associated-consts/shadowed-const.rs b/tests/ui/associated-consts/shadowed-const.rs
index cfdb391d39d..d9b565742d4 100644
--- a/tests/ui/associated-consts/shadowed-const.rs
+++ b/tests/ui/associated-consts/shadowed-const.rs
@@ -17,7 +17,7 @@ trait Baz2: Foo {
 trait Baz3 {
   const BAR: usize;
   const QUX: Self::BAR;
-  //~^ ERROR found associated const
+  //~^ ERROR expected type, found constant
 }
 
 fn main() {}
diff --git a/tests/ui/associated-consts/shadowed-const.stderr b/tests/ui/associated-consts/shadowed-const.stderr
index a01a9ae561f..2db645b3c96 100644
--- a/tests/ui/associated-consts/shadowed-const.stderr
+++ b/tests/ui/associated-consts/shadowed-const.stderr
@@ -1,8 +1,14 @@
-error: found associated const `BAR` when type was expected
-  --> $DIR/shadowed-const.rs:19:14
+error: expected type, found constant
+  --> $DIR/shadowed-const.rs:19:20
    |
 LL |   const QUX: Self::BAR;
-   |              ^^^^^^^^^
+   |                    ^^^ unexpected constant
+   |
+note: the associated constant is defined here
+  --> $DIR/shadowed-const.rs:18:3
+   |
+LL |   const BAR: usize;
+   |   ^^^^^^^^^^^^^^^^
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/associated-type-bounds/consts.rs b/tests/ui/associated-type-bounds/consts.rs
index 9b95b1b52c0..8f90c36ed45 100644
--- a/tests/ui/associated-type-bounds/consts.rs
+++ b/tests/ui/associated-type-bounds/consts.rs
@@ -1,7 +1,7 @@
 #![feature(associated_type_bounds)]
 
 pub fn accept(_: impl Trait<K: Copy>) {}
-//~^ ERROR expected associated type, found associated constant
+//~^ ERROR expected type, found constant
 
 pub trait Trait {
     const K: i32;
diff --git a/tests/ui/associated-type-bounds/consts.stderr b/tests/ui/associated-type-bounds/consts.stderr
index eef24c8827b..7f9fe5e500a 100644
--- a/tests/ui/associated-type-bounds/consts.stderr
+++ b/tests/ui/associated-type-bounds/consts.stderr
@@ -1,10 +1,16 @@
-error: expected associated type, found associated constant
+error: expected type, found constant
   --> $DIR/consts.rs:3:29
    |
 LL | pub fn accept(_: impl Trait<K: Copy>) {}
-   |                             ^
+   |                             ^------ bounds are not allowed on associated constants
+   |                             |
+   |                             unexpected constant
    |
-   = note: trait bounds not allowed on associated constant
+note: the associated constant is defined here
+  --> $DIR/consts.rs:7:5
+   |
+LL |     const K: i32;
+   |     ^^^^^^^^^^^^
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/associated-type-bounds/issue-99828.rs b/tests/ui/associated-type-bounds/issue-99828.rs
index 7b711283f5b..67ba50f3cbc 100644
--- a/tests/ui/associated-type-bounds/issue-99828.rs
+++ b/tests/ui/associated-type-bounds/issue-99828.rs
@@ -1,5 +1,5 @@
 fn get_iter(vec: &[i32]) -> impl Iterator<Item = {}> + '_ {
-    //~^ ERROR expected associated type bound, found constant
+    //~^ ERROR expected type, found constant
     //~| ERROR associated const equality is incomplete
     vec.iter()
 }
diff --git a/tests/ui/associated-type-bounds/issue-99828.stderr b/tests/ui/associated-type-bounds/issue-99828.stderr
index dc93c47dace..8813baf84de 100644
--- a/tests/ui/associated-type-bounds/issue-99828.stderr
+++ b/tests/ui/associated-type-bounds/issue-99828.stderr
@@ -7,13 +7,15 @@ LL | fn get_iter(vec: &[i32]) -> impl Iterator<Item = {}> + '_ {
    = note: see issue #92827 <https://github.com/rust-lang/rust/issues/92827> for more information
    = help: add `#![feature(associated_const_equality)]` to the crate attributes to enable
 
-error: expected associated type bound, found constant
-  --> $DIR/issue-99828.rs:1:43
+error: expected type, found constant
+  --> $DIR/issue-99828.rs:1:50
    |
 LL | fn get_iter(vec: &[i32]) -> impl Iterator<Item = {}> + '_ {
-   |                                           ^^^^^^^^^
+   |                                           ----   ^^ unexpected constant
+   |                                           |
+   |                                           expected a type because of this associated type
    |
-note: associated type defined here
+note: the associated type is defined here
   --> $SRC_DIR/core/src/iter/traits/iterator.rs:LL:COL
 
 error: aborting due to 2 previous errors
diff --git a/tests/ui/associated-type-bounds/return-type-notation/missing.rs b/tests/ui/associated-type-bounds/return-type-notation/missing.rs
index 0679b96f6c5..e6270ec3166 100644
--- a/tests/ui/associated-type-bounds/return-type-notation/missing.rs
+++ b/tests/ui/associated-type-bounds/return-type-notation/missing.rs
@@ -8,6 +8,6 @@ trait Trait {
 }
 
 fn bar<T: Trait<methid(): Send>>() {}
-//~^ ERROR cannot find associated function `methid` for `Trait`
+//~^ ERROR associated function `methid` not found for `Trait`
 
 fn main() {}
diff --git a/tests/ui/associated-type-bounds/return-type-notation/missing.stderr b/tests/ui/associated-type-bounds/return-type-notation/missing.stderr
index 3ca5e66866d..db9cb9f49a3 100644
--- a/tests/ui/associated-type-bounds/return-type-notation/missing.stderr
+++ b/tests/ui/associated-type-bounds/return-type-notation/missing.stderr
@@ -7,11 +7,12 @@ LL | #![feature(return_type_notation)]
    = note: see issue #109417 <https://github.com/rust-lang/rust/issues/109417> for more information
    = note: `#[warn(incomplete_features)]` on by default
 
-error: cannot find associated function `methid` for `Trait`
+error[E0220]: associated function `methid` not found for `Trait`
   --> $DIR/missing.rs:10:17
    |
 LL | fn bar<T: Trait<methid(): Send>>() {}
-   |                 ^^^^^^^^^^^^^^
+   |                 ^^^^^^ help: there is an associated function with a similar name: `method`
 
 error: aborting due to 1 previous error; 1 warning emitted
 
+For more information about this error, try `rustc --explain E0220`.
diff --git a/tests/ui/async-await/return-type-notation/super-method-bound-ambig.rs b/tests/ui/async-await/return-type-notation/super-method-bound-ambig.rs
index 891b30638ee..73c08531599 100644
--- a/tests/ui/async-await/return-type-notation/super-method-bound-ambig.rs
+++ b/tests/ui/async-await/return-type-notation/super-method-bound-ambig.rs
@@ -23,7 +23,7 @@ impl Foo for () {}
 fn test<T>()
 where
     T: Foo<test(): Send>,
-    //~^ ERROR ambiguous associated function `test` for `Foo`
+    //~^ ERROR ambiguous associated function `test` in bounds of `Foo`
 {
 }
 
diff --git a/tests/ui/async-await/return-type-notation/super-method-bound-ambig.stderr b/tests/ui/async-await/return-type-notation/super-method-bound-ambig.stderr
index 7eaf3b82d98..4003aad6d03 100644
--- a/tests/ui/async-await/return-type-notation/super-method-bound-ambig.stderr
+++ b/tests/ui/async-await/return-type-notation/super-method-bound-ambig.stderr
@@ -7,13 +7,18 @@ LL | #![feature(return_type_notation)]
    = note: see issue #109417 <https://github.com/rust-lang/rust/issues/109417> for more information
    = note: `#[warn(incomplete_features)]` on by default
 
-error: ambiguous associated function `test` for `Foo`
+error[E0221]: ambiguous associated function `test` in bounds of `Foo`
   --> $DIR/super-method-bound-ambig.rs:25:12
    |
+LL |     async fn test();
+   |     ---------------- ambiguous `test` from `for<'a> Super1<'a>`
+...
+LL |     async fn test();
+   |     ---------------- ambiguous `test` from `Super2`
+...
 LL |     T: Foo<test(): Send>,
-   |            ^^^^^^^^^^^^
-   |
-   = note: `test` is declared in two supertraits: `Super2` and `Super1<'a>`
+   |            ^^^^^^^^^^^^ ambiguous associated function `test`
 
 error: aborting due to 1 previous error; 1 warning emitted
 
+For more information about this error, try `rustc --explain E0221`.
diff --git a/tests/ui/const-generics/assoc_const_eq_diagnostic.rs b/tests/ui/const-generics/assoc_const_eq_diagnostic.rs
index bf8202ac152..d51696f9ebd 100644
--- a/tests/ui/const-generics/assoc_const_eq_diagnostic.rs
+++ b/tests/ui/const-generics/assoc_const_eq_diagnostic.rs
@@ -9,9 +9,9 @@ pub trait Parse {
 }
 
 pub trait CoolStuff: Parse<MODE = Mode::Cool> {}
-//~^ ERROR expected associated constant bound
-//~| ERROR expected associated constant bound
-//~| ERROR expected type
+//~^ ERROR expected type, found variant
+//~| ERROR expected constant, found type
+//~| ERROR expected constant, found type
 
 fn no_help() -> Mode::Cool {}
 //~^ ERROR expected type, found variant
diff --git a/tests/ui/const-generics/assoc_const_eq_diagnostic.stderr b/tests/ui/const-generics/assoc_const_eq_diagnostic.stderr
index 6d5cd45479e..3d724bb1642 100644
--- a/tests/ui/const-generics/assoc_const_eq_diagnostic.stderr
+++ b/tests/ui/const-generics/assoc_const_eq_diagnostic.stderr
@@ -16,30 +16,42 @@ LL | fn no_help() -> Mode::Cool {}
    |                 not a type
    |                 help: try using the variant's enum: `Mode`
 
-error: expected associated constant bound, found type
-  --> $DIR/assoc_const_eq_diagnostic.rs:11:28
+error: expected constant, found type
+  --> $DIR/assoc_const_eq_diagnostic.rs:11:35
    |
 LL | pub trait CoolStuff: Parse<MODE = Mode::Cool> {}
-   |                            ^^^^^^^^^^^^^^^^^ help: if equating a const, try wrapping with braces: `MODE = { const }`
+   |                            ----   ^^^^^^^^^^ unexpected type
+   |                            |
+   |                            expected a constant because of this associated constant
    |
-note: associated constant defined here
+note: the associated constant is defined here
   --> $DIR/assoc_const_eq_diagnostic.rs:8:5
    |
 LL |     const MODE: Mode;
    |     ^^^^^^^^^^^^^^^^
+help: consider adding braces here
+   |
+LL | pub trait CoolStuff: Parse<MODE = { Mode::Cool }> {}
+   |                                   +            +
 
-error: expected associated constant bound, found type
-  --> $DIR/assoc_const_eq_diagnostic.rs:11:28
+error: expected constant, found type
+  --> $DIR/assoc_const_eq_diagnostic.rs:11:35
    |
 LL | pub trait CoolStuff: Parse<MODE = Mode::Cool> {}
-   |                            ^^^^^^^^^^^^^^^^^ help: if equating a const, try wrapping with braces: `MODE = { const }`
+   |                            ----   ^^^^^^^^^^ unexpected type
+   |                            |
+   |                            expected a constant because of this associated constant
    |
-note: associated constant defined here
+note: the associated constant is defined here
   --> $DIR/assoc_const_eq_diagnostic.rs:8:5
    |
 LL |     const MODE: Mode;
    |     ^^^^^^^^^^^^^^^^
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+help: consider adding braces here
+   |
+LL | pub trait CoolStuff: Parse<MODE = { Mode::Cool }> {}
+   |                                   +            +
 
 error: aborting due to 4 previous errors
 
diff --git a/tests/ui/error-codes/E0221.stderr b/tests/ui/error-codes/E0221.stderr
index e600acf7834..07e7485b67e 100644
--- a/tests/ui/error-codes/E0221.stderr
+++ b/tests/ui/error-codes/E0221.stderr
@@ -28,7 +28,7 @@ LL |     fn test() {
 LL |         let _: Self::Err;
    |                ^^^^^^^^^ ambiguous associated type `Err`
    |
-   = note: associated type `Self` could derive from `FromStr`
+   = note: associated type `Err` could derive from `FromStr`
 help: use fully-qualified syntax to disambiguate
    |
 LL |         let _: <Self as My>::Err;
diff --git a/tests/ui/feature-gates/feature-gate-return_type_notation.cfg.stderr b/tests/ui/feature-gates/feature-gate-return_type_notation.cfg.stderr
index 1bdb2574ead..a15b01618f5 100644
--- a/tests/ui/feature-gates/feature-gate-return_type_notation.cfg.stderr
+++ b/tests/ui/feature-gates/feature-gate-return_type_notation.cfg.stderr
@@ -15,13 +15,18 @@ LL | fn foo<T: Trait<m(): Send>>() {}
    |                  |
    |                  help: remove these parentheses
 
-error[E0220]: associated type `m` not found for `Trait`
+error: expected type, found function
   --> $DIR/feature-gate-return_type_notation.rs:14:17
    |
 LL | fn foo<T: Trait<m(): Send>>() {}
-   |                 ^ associated type `m` not found
+   |                 ^ unexpected function
+   |
+note: the associated function is defined here
+  --> $DIR/feature-gate-return_type_notation.rs:10:5
+   |
+LL |     async fn m();
+   |     ^^^^^^^^^^^^^
 
 error: aborting due to 3 previous errors
 
-Some errors have detailed explanations: E0220, E0658.
-For more information about an error, try `rustc --explain E0220`.
+For more information about this error, try `rustc --explain E0658`.
diff --git a/tests/ui/feature-gates/feature-gate-return_type_notation.rs b/tests/ui/feature-gates/feature-gate-return_type_notation.rs
index 86e2c48e188..60ac9f8d4f1 100644
--- a/tests/ui/feature-gates/feature-gate-return_type_notation.rs
+++ b/tests/ui/feature-gates/feature-gate-return_type_notation.rs
@@ -14,7 +14,7 @@ trait Trait {
 fn foo<T: Trait<m(): Send>>() {}
 //[cfg]~^ ERROR return type notation is experimental
 //[cfg]~| ERROR parenthesized generic arguments cannot be used in associated type constraints
-//[cfg]~| ERROR associated type `m` not found for `Trait`
+//[cfg]~| ERROR expected type, found function
 //[no]~^^^^ WARN return type notation is experimental
 //[no]~| WARN unstable syntax can change at any point in the future, causing a hard error!