Fixing bad suggestion for _ in const type when a function #81885

compiler/rustc_typeck/src/astconv/mod.rs

@@ -2327,6 +2327,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 &generics.params[..],
                 visitor.0,
                 true,
+                true
             );
         }
 

compiler/rustc_typeck/src/collect.rs

@@ -141,6 +141,7 @@ crate fn placeholder_type_error(
     generics: &[hir::GenericParam<'_>],
     placeholder_types: Vec<Span>,
     suggest: bool,
+    is_fn: bool,
 ) {
     if placeholder_types.is_empty() {
         return;
@@ -171,7 +172,9 @@ crate fn placeholder_type_error(
     }
 
     let mut err = bad_placeholder_type(tcx, placeholder_types);
-    if suggest {
+    
+    // Suggest, but only if it is not a function
+    if suggest && !is_fn {
         err.multipart_suggestion(
             "use type parameters instead",
             sugg,
@@ -198,7 +201,14 @@ fn reject_placeholder_type_signatures_in_item(tcx: TyCtxt<'tcx>, item: &'tcx hir
     let mut visitor = PlaceholderHirTyCollector::default();
     visitor.visit_item(item);
 
-    placeholder_type_error(tcx, Some(generics.span), &generics.params[..], visitor.0, suggest);
+    placeholder_type_error(
+        tcx, 
+        Some(generics.span), 
+        &generics.params[..], 
+        visitor.0, 
+        suggest, 
+        false
+    );
 }
 
 impl Visitor<'tcx> for CollectItemTypesVisitor<'tcx> {
@@ -743,7 +753,7 @@ fn convert_trait_item(tcx: TyCtxt<'_>, trait_item_id: hir::HirId) {
             // Account for `const C: _;`.
             let mut visitor = PlaceholderHirTyCollector::default();
             visitor.visit_trait_item(trait_item);
-            placeholder_type_error(tcx, None, &[], visitor.0, false);
+            placeholder_type_error(tcx, None, &[], visitor.0, false, false);
         }
 
         hir::TraitItemKind::Type(_, Some(_)) => {
@@ -752,7 +762,7 @@ fn convert_trait_item(tcx: TyCtxt<'_>, trait_item_id: hir::HirId) {
             // Account for `type T = _;`.
             let mut visitor = PlaceholderHirTyCollector::default();
             visitor.visit_trait_item(trait_item);
-            placeholder_type_error(tcx, None, &[], visitor.0, false);
+            placeholder_type_error(tcx, None, &[], visitor.0, false, false);
         }
 
         hir::TraitItemKind::Type(_, None) => {
@@ -761,7 +771,7 @@ fn convert_trait_item(tcx: TyCtxt<'_>, trait_item_id: hir::HirId) {
             // even if there is no concrete type.
             let mut visitor = PlaceholderHirTyCollector::default();
             visitor.visit_trait_item(trait_item);
-            placeholder_type_error(tcx, None, &[], visitor.0, false);
+            placeholder_type_error(tcx, None, &[], visitor.0, false, false);
         }
     };
 
@@ -782,7 +792,7 @@ fn convert_impl_item(tcx: TyCtxt<'_>, impl_item_id: hir::HirId) {
             // Account for `type T = _;`
             let mut visitor = PlaceholderHirTyCollector::default();
             visitor.visit_impl_item(impl_item);
-            placeholder_type_error(tcx, None, &[], visitor.0, false);
+            placeholder_type_error(tcx, None, &[], visitor.0, false, false);
         }
         hir::ImplItemKind::Const(..) => {}
     }

src/test/ui/did_you_mean/bad-assoc-ty.stderr

@@ -129,33 +129,18 @@ LL | fn foo<X: K<_, _>>(x: X) {}
    |             ^  ^ not allowed in type signatures
    |             |
    |             not allowed in type signatures
-   |
-help: use type parameters instead
-   |
-LL | fn foo<X: K<T, T>, T>(x: X) {}
-   |             ^  ^ ^^^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
   --> $DIR/bad-assoc-ty.rs:52:34
    |
 LL | fn bar<F>(_: F) where F: Fn() -> _ {}
    |                                  ^ not allowed in type signatures
-   |
-help: use type parameters instead
-   |
-LL | fn bar<F, T>(_: F) where F: Fn() -> T {}
-   |         ^^^                         ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
   --> $DIR/bad-assoc-ty.rs:55:19
    |
 LL | fn baz<F: Fn() -> _>(_: F) {}
    |                   ^ not allowed in type signatures
-   |
-help: use type parameters instead
-   |
-LL | fn baz<F: Fn() -> T, T>(_: F) {}
-   |                   ^^^^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
   --> $DIR/bad-assoc-ty.rs:58:33
@@ -217,11 +202,6 @@ error[E0121]: the type placeholder `_` is not allowed within types on item signa
    |
 LL |     fn foo<F>(_: F) where F: Fn() -> _ {}
    |                                      ^ not allowed in type signatures
-   |
-help: use type parameters instead
-   |
-LL |     fn foo<F, T>(_: F) where F: Fn() -> T {}
-   |             ^^^                         ^
 
 error: aborting due to 28 previous errors
 

src/test/ui/issues/issue-74086.stderr

@@ -2,10 +2,7 @@ error[E0121]: the type placeholder `_` is not allowed within types on item signa
   --> $DIR/issue-74086.rs:2:20
    |
 LL |     static BUG: fn(_) -> u8 = |_| 8;
-   |                    ^
+   |                    ^ not allowed in type signatures
-   |                    |
-   |                    not allowed in type signatures
-   |                    help: use type parameters instead: `T`
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-81885.rs

@@ -0,0 +1,10 @@
+const TEST4: fn() -> _ = 42;
+                  //~^ ERROR the type placeholder `_` is not allowed within types on item
+                  //signatures
+
+fn main() {
+    const TEST5: fn() -> _ = 42;
+                      //~^ ERROR the type placeholder `_` is not allowed within types on item
+                      //signatures
+
+}

src/test/ui/issues/issue-81885.stderr

@@ -0,0 +1,15 @@
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/issue-81885.rs:1:22
+   |
+LL | const TEST4: fn() -> _ = 42;
+   |                      ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/issue-81885.rs:6:26
+   |
+LL |     const TEST5: fn() -> _ = 42;
+   |                          ^ not allowed in type signatures
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0121`.

src/test/ui/self/self-infer.stderr

@@ -3,22 +3,12 @@ error[E0121]: the type placeholder `_` is not allowed within types on item signa
    |
 LL |     fn f(self: _) {}
    |                ^ not allowed in type signatures
-   |
-help: use type parameters instead
-   |
-LL |     fn f<T>(self: T) {}
-   |         ^^^       ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
   --> $DIR/self-infer.rs:5:17
    |
 LL |     fn g(self: &_) {}
    |                 ^ not allowed in type signatures
-   |
-help: use type parameters instead
-   |
-LL |     fn g<T>(self: &T) {}
-   |         ^^^        ^
 
 error: aborting due to 2 previous errors
 

src/test/ui/typeck/typeck_type_placeholder_item.stderr

@@ -92,64 +92,36 @@ error[E0121]: the type placeholder `_` is not allowed within types on item signa
    |
 LL | fn test6(_: _) { }
    |             ^ not allowed in type signatures
-   |
-help: use type parameters instead
-   |
-LL | fn test6<T>(_: T) { }
-   |         ^^^    ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
   --> $DIR/typeck_type_placeholder_item.rs:24:18
    |
 LL | fn test6_b<T>(_: _, _: T) { }
    |                  ^ not allowed in type signatures
-   |
-help: use type parameters instead
-   |
-LL | fn test6_b<T, U>(_: U, _: T) { }
-   |             ^^^     ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
   --> $DIR/typeck_type_placeholder_item.rs:27:30
    |
 LL | fn test6_c<T, K, L, A, B>(_: _, _: (T, K, L, A, B)) { }
    |                              ^ not allowed in type signatures
-   |
-help: use type parameters instead
-   |
-LL | fn test6_c<T, K, L, A, B, U>(_: U, _: (T, K, L, A, B)) { }
-   |                         ^^^     ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
   --> $DIR/typeck_type_placeholder_item.rs:30:13
    |
 LL | fn test7(x: _) { let _x: usize = x; }
    |             ^ not allowed in type signatures
-   |
-help: use type parameters instead
-   |
-LL | fn test7<T>(x: T) { let _x: usize = x; }
-   |         ^^^    ^
-
-error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:33:22
-   |
-LL | fn test8(_f: fn() -> _) { }
-   |                      ^
-   |                      |
-   |                      not allowed in type signatures
-   |                      help: use type parameters instead: `T`
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
   --> $DIR/typeck_type_placeholder_item.rs:33:22
    |
 LL | fn test8(_f: fn() -> _) { }
    |                      ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:33:22
    |
-help: use type parameters instead
+LL | fn test8(_f: fn() -> _) { }
-   |
+   |                      ^ not allowed in type signatures
-LL | fn test8<T>(_f: fn() -> T) { }
-   |         ^^^             ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
   --> $DIR/typeck_type_placeholder_item.rs:47:26
@@ -257,42 +229,24 @@ error[E0121]: the type placeholder `_` is not allowed within types on item signa
    |
 LL |     fn fn_test6(_: _) { }
    |                    ^ not allowed in type signatures
-   |
-help: use type parameters instead
-   |
-LL |     fn fn_test6<T>(_: T) { }
-   |                ^^^    ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
   --> $DIR/typeck_type_placeholder_item.rs:97:20
    |
 LL |     fn fn_test7(x: _) { let _x: usize = x; }
    |                    ^ not allowed in type signatures
-   |
-help: use type parameters instead
-   |
-LL |     fn fn_test7<T>(x: T) { let _x: usize = x; }
-   |                ^^^    ^
-
-error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/typeck_type_placeholder_item.rs:100:29
-   |
-LL |     fn fn_test8(_f: fn() -> _) { }
-   |                             ^
-   |                             |
-   |                             not allowed in type signatures
-   |                             help: use type parameters instead: `T`
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
   --> $DIR/typeck_type_placeholder_item.rs:100:29
    |
 LL |     fn fn_test8(_f: fn() -> _) { }
    |                             ^ not allowed in type signatures
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/typeck_type_placeholder_item.rs:100:29
    |
-help: use type parameters instead
+LL |     fn fn_test8(_f: fn() -> _) { }
-   |
+   |                             ^ not allowed in type signatures
-LL |     fn fn_test8<T>(_f: fn() -> T) { }
-   |                ^^^             ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
   --> $DIR/typeck_type_placeholder_item.rs:123:12
@@ -415,11 +369,6 @@ error[E0121]: the type placeholder `_` is not allowed within types on item signa
    |
 LL |     fn method_test1(&self, x: _);
    |                               ^ not allowed in type signatures
-   |
-help: use type parameters instead
-   |
-LL |     fn method_test1<T>(&self, x: T);
-   |                    ^^^           ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
   --> $DIR/typeck_type_placeholder_item.rs:142:31
@@ -428,33 +377,18 @@ LL |     fn method_test2(&self, x: _) -> _;
    |                               ^     ^ not allowed in type signatures
    |                               |
    |                               not allowed in type signatures
-   |
-help: use type parameters instead
-   |
-LL |     fn method_test2<T>(&self, x: T) -> T;
-   |                    ^^^           ^     ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
   --> $DIR/typeck_type_placeholder_item.rs:144:31
    |
 LL |     fn method_test3(&self) -> _;
    |                               ^ not allowed in type signatures
-   |
-help: use type parameters instead
-   |
-LL |     fn method_test3<T>(&self) -> T;
-   |                    ^^^           ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
   --> $DIR/typeck_type_placeholder_item.rs:146:26
    |
 LL |     fn assoc_fn_test1(x: _);
    |                          ^ not allowed in type signatures
-   |
-help: use type parameters instead
-   |
-LL |     fn assoc_fn_test1<T>(x: T);
-   |                      ^^^    ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
   --> $DIR/typeck_type_placeholder_item.rs:148:26
@@ -463,22 +397,12 @@ LL |     fn assoc_fn_test2(x: _) -> _;
    |                          ^     ^ not allowed in type signatures
    |                          |
    |                          not allowed in type signatures
-   |
-help: use type parameters instead
-   |
-LL |     fn assoc_fn_test2<T>(x: T) -> T;
-   |                      ^^^    ^     ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
   --> $DIR/typeck_type_placeholder_item.rs:150:28
    |
 LL |     fn assoc_fn_test3() -> _;
    |                            ^ not allowed in type signatures
-   |
-help: use type parameters instead
-   |
-LL |     fn assoc_fn_test3<T>() -> T;
-   |                      ^^^      ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
   --> $DIR/typeck_type_placeholder_item.rs:190:14
@@ -521,11 +445,6 @@ error[E0121]: the type placeholder `_` is not allowed within types on item signa
    |
 LL |     fn test10(&self, _x : _) { }
    |                           ^ not allowed in type signatures
-   |
-help: use type parameters instead
-   |
-LL |     fn test10<T>(&self, _x : T) { }
-   |              ^^^             ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
   --> $DIR/typeck_type_placeholder_item.rs:58:24
@@ -541,11 +460,6 @@ error[E0121]: the type placeholder `_` is not allowed within types on item signa
    |
 LL |     fn clone_from(&mut self, other: _) { *self = Test9; }
    |                                     ^ not allowed in type signatures
-   |
-help: use type parameters instead
-   |
-LL |     fn clone_from<T>(&mut self, other: T) { *self = Test9; }
-   |                  ^^^                   ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
   --> $DIR/typeck_type_placeholder_item.rs:107:31
@@ -561,11 +475,6 @@ error[E0121]: the type placeholder `_` is not allowed within types on item signa
    |
 LL |         fn fn_test10(&self, _x : _) { }
    |                                  ^ not allowed in type signatures
-   |
-help: use type parameters instead
-   |
-LL |         fn fn_test10<T>(&self, _x : T) { }
-   |                     ^^^             ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
   --> $DIR/typeck_type_placeholder_item.rs:115:28
@@ -581,11 +490,6 @@ error[E0121]: the type placeholder `_` is not allowed within types on item signa
    |
 LL |         fn clone_from(&mut self, other: _) { *self = FnTest9; }
    |                                         ^ not allowed in type signatures
-   |
-help: use type parameters instead
-   |
-LL |         fn clone_from<T>(&mut self, other: T) { *self = FnTest9; }
-   |                      ^^^                   ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
   --> $DIR/typeck_type_placeholder_item.rs:201:14

src/test/ui/typeck/typeck_type_placeholder_item_help.stderr

@@ -29,10 +29,7 @@ error[E0121]: the type placeholder `_` is not allowed within types on item signa
   --> $DIR/typeck_type_placeholder_item_help.rs:13:22
    |
 LL | const TEST4: fn() -> _ = 42;
-   |                      ^
+   |                      ^ not allowed in type signatures
-   |                      |
-   |                      not allowed in type signatures
-   |                      help: use type parameters instead: `T`
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
   --> $DIR/typeck_type_placeholder_item_help.rs:17:18