Rollup merge of #106176 - compiler-errors:fn-kw-as-fn-trait, r=estebank

Recover `fn` keyword as `Fn` trait in bounds

`impl fn()` -> `impl Fn()`

Fixes #82515

4 files changed, 90 insertions, 74 deletions

diff --git a/src/test/ui/parser/kw-in-trait-bounds.rs b/src/test/ui/parser/kw-in-trait-bounds.rs
index fa037e5937d..e9e85339aff 100644
--- a/src/test/ui/parser/kw-in-trait-bounds.rs
+++ b/src/test/ui/parser/kw-in-trait-bounds.rs
@@ -4,21 +4,13 @@ fn _f<F: fn(), G>(_: impl fn(), _: &dyn fn())
 //~^ ERROR expected identifier, found keyword `fn`
 //~| ERROR expected identifier, found keyword `fn`
 //~| ERROR expected identifier, found keyword `fn`
-//~| ERROR cannot find trait `r#fn` in this scope
-//~| ERROR cannot find trait `r#fn` in this scope
-//~| ERROR cannot find trait `r#fn` in this scope
-//~| HELP  a trait with a similar name exists
-//~| HELP  a trait with a similar name exists
-//~| HELP  a trait with a similar name exists
-//~| HELP  escape `fn` to use it as an identifier
-//~| HELP  escape `fn` to use it as an identifier
-//~| HELP  escape `fn` to use it as an identifier
+//~| HELP use `Fn` to refer to the trait
+//~| HELP use `Fn` to refer to the trait
+//~| HELP use `Fn` to refer to the trait
 where
 G: fn(),
     //~^ ERROR expected identifier, found keyword `fn`
-    //~| ERROR cannot find trait `r#fn` in this scope
-    //~| HELP  a trait with a similar name exists
-    //~| HELP  escape `fn` to use it as an identifier
+    //~| HELP use `Fn` to refer to the trait
 {}
 
 fn _g<A: struct, B>(_: impl struct, _: &dyn struct)
diff --git a/src/test/ui/parser/kw-in-trait-bounds.stderr b/src/test/ui/parser/kw-in-trait-bounds.stderr
index 79643660e8b..2d3aad4d6ba 100644
--- a/src/test/ui/parser/kw-in-trait-bounds.stderr
+++ b/src/test/ui/parser/kw-in-trait-bounds.stderr
@@ -2,48 +2,48 @@ error: expected identifier, found keyword `fn`
   --> $DIR/kw-in-trait-bounds.rs:3:10
    |
 LL | fn _f<F: fn(), G>(_: impl fn(), _: &dyn fn())
-   |          ^^ expected identifier, found keyword
+   |          ^^
    |
-help: escape `fn` to use it as an identifier
+help: use `Fn` to refer to the trait
    |
-LL | fn _f<F: r#fn(), G>(_: impl fn(), _: &dyn fn())
-   |          ++
+LL | fn _f<F: Fn(), G>(_: impl fn(), _: &dyn fn())
+   |          ~~
 
 error: expected identifier, found keyword `fn`
   --> $DIR/kw-in-trait-bounds.rs:3:27
    |
 LL | fn _f<F: fn(), G>(_: impl fn(), _: &dyn fn())
-   |                           ^^ expected identifier, found keyword
+   |                           ^^
    |
-help: escape `fn` to use it as an identifier
+help: use `Fn` to refer to the trait
    |
-LL | fn _f<F: fn(), G>(_: impl r#fn(), _: &dyn fn())
-   |                           ++
+LL | fn _f<F: fn(), G>(_: impl Fn(), _: &dyn fn())
+   |                           ~~
 
 error: expected identifier, found keyword `fn`
   --> $DIR/kw-in-trait-bounds.rs:3:41
    |
 LL | fn _f<F: fn(), G>(_: impl fn(), _: &dyn fn())
-   |                                         ^^ expected identifier, found keyword
+   |                                         ^^
    |
-help: escape `fn` to use it as an identifier
+help: use `Fn` to refer to the trait
    |
-LL | fn _f<F: fn(), G>(_: impl fn(), _: &dyn r#fn())
-   |                                         ++
+LL | fn _f<F: fn(), G>(_: impl fn(), _: &dyn Fn())
+   |                                         ~~
 
 error: expected identifier, found keyword `fn`
-  --> $DIR/kw-in-trait-bounds.rs:17:4
+  --> $DIR/kw-in-trait-bounds.rs:11:4
    |
 LL | G: fn(),
-   |    ^^ expected identifier, found keyword
+   |    ^^
    |
-help: escape `fn` to use it as an identifier
+help: use `Fn` to refer to the trait
    |
-LL | G: r#fn(),
-   |    ++
+LL | G: Fn(),
+   |    ~~
 
 error: expected identifier, found keyword `struct`
-  --> $DIR/kw-in-trait-bounds.rs:24:10
+  --> $DIR/kw-in-trait-bounds.rs:16:10
    |
 LL | fn _g<A: struct, B>(_: impl struct, _: &dyn struct)
    |          ^^^^^^ expected identifier, found keyword
@@ -54,7 +54,7 @@ LL | fn _g<A: r#struct, B>(_: impl struct, _: &dyn struct)
    |          ++
 
 error: expected identifier, found keyword `struct`
-  --> $DIR/kw-in-trait-bounds.rs:24:29
+  --> $DIR/kw-in-trait-bounds.rs:16:29
    |
 LL | fn _g<A: struct, B>(_: impl struct, _: &dyn struct)
    |                             ^^^^^^ expected identifier, found keyword
@@ -65,7 +65,7 @@ LL | fn _g<A: struct, B>(_: impl r#struct, _: &dyn struct)
    |                             ++
 
 error: expected identifier, found keyword `struct`
-  --> $DIR/kw-in-trait-bounds.rs:24:45
+  --> $DIR/kw-in-trait-bounds.rs:16:45
    |
 LL | fn _g<A: struct, B>(_: impl struct, _: &dyn struct)
    |                                             ^^^^^^ expected identifier, found keyword
@@ -76,7 +76,7 @@ LL | fn _g<A: struct, B>(_: impl struct, _: &dyn r#struct)
    |                                             ++
 
 error: expected identifier, found keyword `struct`
-  --> $DIR/kw-in-trait-bounds.rs:38:8
+  --> $DIR/kw-in-trait-bounds.rs:30:8
    |
 LL |     B: struct,
    |        ^^^^^^ expected identifier, found keyword
@@ -86,44 +86,8 @@ help: escape `struct` to use it as an identifier
 LL |     B: r#struct,
    |        ++
 
-error[E0405]: cannot find trait `r#fn` in this scope
-  --> $DIR/kw-in-trait-bounds.rs:3:10
-   |
-LL | fn _f<F: fn(), G>(_: impl fn(), _: &dyn fn())
-   |          ^^ help: a trait with a similar name exists (notice the capitalization): `Fn`
-  --> $SRC_DIR/core/src/ops/function.rs:LL:COL
-   |
-   = note: similarly named trait `Fn` defined here
-
-error[E0405]: cannot find trait `r#fn` in this scope
-  --> $DIR/kw-in-trait-bounds.rs:17:4
-   |
-LL | G: fn(),
-   |    ^^ help: a trait with a similar name exists (notice the capitalization): `Fn`
-  --> $SRC_DIR/core/src/ops/function.rs:LL:COL
-   |
-   = note: similarly named trait `Fn` defined here
-
-error[E0405]: cannot find trait `r#fn` in this scope
-  --> $DIR/kw-in-trait-bounds.rs:3:27
-   |
-LL | fn _f<F: fn(), G>(_: impl fn(), _: &dyn fn())
-   |                           ^^ help: a trait with a similar name exists (notice the capitalization): `Fn`
-  --> $SRC_DIR/core/src/ops/function.rs:LL:COL
-   |
-   = note: similarly named trait `Fn` defined here
-
-error[E0405]: cannot find trait `r#fn` in this scope
-  --> $DIR/kw-in-trait-bounds.rs:3:41
-   |
-LL | fn _f<F: fn(), G>(_: impl fn(), _: &dyn fn())
-   |                                         ^^ help: a trait with a similar name exists (notice the capitalization): `Fn`
-  --> $SRC_DIR/core/src/ops/function.rs:LL:COL
-   |
-   = note: similarly named trait `Fn` defined here
-
 error[E0405]: cannot find trait `r#struct` in this scope
-  --> $DIR/kw-in-trait-bounds.rs:24:10
+  --> $DIR/kw-in-trait-bounds.rs:16:10
    |
 LL | fn _g<A: struct, B>(_: impl struct, _: &dyn struct)
    |          ^^^^^^ help: a trait with a similar name exists (notice the capitalization): `Struct`
@@ -132,7 +96,7 @@ LL | trait Struct {}
    | ------------ similarly named trait `Struct` defined here
 
 error[E0405]: cannot find trait `r#struct` in this scope
-  --> $DIR/kw-in-trait-bounds.rs:38:8
+  --> $DIR/kw-in-trait-bounds.rs:30:8
    |
 LL |     B: struct,
    |        ^^^^^^ help: a trait with a similar name exists (notice the capitalization): `Struct`
@@ -141,7 +105,7 @@ LL | trait Struct {}
    | ------------ similarly named trait `Struct` defined here
 
 error[E0405]: cannot find trait `r#struct` in this scope
-  --> $DIR/kw-in-trait-bounds.rs:24:29
+  --> $DIR/kw-in-trait-bounds.rs:16:29
    |
 LL | fn _g<A: struct, B>(_: impl struct, _: &dyn struct)
    |                             ^^^^^^ help: a trait with a similar name exists (notice the capitalization): `Struct`
@@ -150,7 +114,7 @@ LL | trait Struct {}
    | ------------ similarly named trait `Struct` defined here
 
 error[E0405]: cannot find trait `r#struct` in this scope
-  --> $DIR/kw-in-trait-bounds.rs:24:45
+  --> $DIR/kw-in-trait-bounds.rs:16:45
    |
 LL | fn _g<A: struct, B>(_: impl struct, _: &dyn struct)
    |                                             ^^^^^^ help: a trait with a similar name exists (notice the capitalization): `Struct`
@@ -158,6 +122,6 @@ LL | fn _g<A: struct, B>(_: impl struct, _: &dyn struct)
 LL | trait Struct {}
    | ------------ similarly named trait `Struct` defined here
 
-error: aborting due to 16 previous errors
+error: aborting due to 12 previous errors
 
 For more information about this error, try `rustc --explain E0405`.
diff --git a/src/test/ui/parser/recover-fn-trait-from-fn-kw.rs b/src/test/ui/parser/recover-fn-trait-from-fn-kw.rs
new file mode 100644
index 00000000000..b6611e6273d
--- /dev/null
+++ b/src/test/ui/parser/recover-fn-trait-from-fn-kw.rs
@@ -0,0 +1,12 @@
+fn foo(_: impl fn() -> i32) {}
+//~^ ERROR expected identifier, found keyword `fn`
+
+fn foo2<T: fn(i32)>(_: T) {}
+//~^ ERROR expected identifier, found keyword `fn`
+
+fn main() {
+    foo(|| ());
+    //~^ mismatched types
+    foo2(|_: ()| {});
+    //~^ type mismatch in closure arguments
+}
diff --git a/src/test/ui/parser/recover-fn-trait-from-fn-kw.stderr b/src/test/ui/parser/recover-fn-trait-from-fn-kw.stderr
new file mode 100644
index 00000000000..3681a796c53
--- /dev/null
+++ b/src/test/ui/parser/recover-fn-trait-from-fn-kw.stderr
@@ -0,0 +1,48 @@
+error: expected identifier, found keyword `fn`
+  --> $DIR/recover-fn-trait-from-fn-kw.rs:1:16
+   |
+LL | fn foo(_: impl fn() -> i32) {}
+   |                ^^
+   |
+help: use `Fn` to refer to the trait
+   |
+LL | fn foo(_: impl Fn() -> i32) {}
+   |                ~~
+
+error: expected identifier, found keyword `fn`
+  --> $DIR/recover-fn-trait-from-fn-kw.rs:4:12
+   |
+LL | fn foo2<T: fn(i32)>(_: T) {}
+   |            ^^
+   |
+help: use `Fn` to refer to the trait
+   |
+LL | fn foo2<T: Fn(i32)>(_: T) {}
+   |            ~~
+
+error[E0308]: mismatched types
+  --> $DIR/recover-fn-trait-from-fn-kw.rs:8:12
+   |
+LL |     foo(|| ());
+   |            ^^ expected `i32`, found `()`
+
+error[E0631]: type mismatch in closure arguments
+  --> $DIR/recover-fn-trait-from-fn-kw.rs:10:5
+   |
+LL |     foo2(|_: ()| {});
+   |     ^^^^ ------- found signature defined here
+   |     |
+   |     expected due to this
+   |
+   = note: expected closure signature `fn(i32) -> _`
+              found closure signature `fn(()) -> _`
+note: required by a bound in `foo2`
+  --> $DIR/recover-fn-trait-from-fn-kw.rs:4:12
+   |
+LL | fn foo2<T: fn(i32)>(_: T) {}
+   |            ^^^^^^^ required by this bound in `foo2`
+
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0308, E0631.
+For more information about an error, try `rustc --explain E0308`.