Rollup merge of #84316 - teymour-aldridge:improve-defaulted-never-note, r=petrochenkov

Improve an error message.

Author: GuillaumeGomez

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

@@ -503,14 +503,14 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                             let unit_obligation =
                                 obligation.with(predicate.without_const().to_predicate(tcx));
                             if self.predicate_may_hold(&unit_obligation) {
+                                err.note("this trait is implemented for `()`.");
                                 err.note(
-                                    "the trait is implemented for `()`. \
-                                     Possibly this error has been caused by changes to \
-                                     Rust's type-inference algorithm (see issue #48950 \
-                                     <https://github.com/rust-lang/rust/issues/48950> \
-                                     for more information). Consider whether you meant to use \
-                                     the type `()` here instead.",
+                                    "this error might have been caused by changes to \
+                                    Rust's type-inference algorithm (see issue #48950 \
+                                    <https://github.com/rust-lang/rust/issues/48950> \
+                                    for more information).",
                                 );
+                                err.help("did you intend to use the type `()` here instead?");
                             }
                         }
 

src/test/ui/never_type/defaulted-never-note.rs

@@ -26,7 +26,9 @@ fn smeg() {
     foo(_x);
     //~^ ERROR the trait bound
     //~| NOTE the trait `ImplementedForUnitButNotNever` is not implemented
-    //~| NOTE the trait is implemented for `()`
+    //~| NOTE this trait is implemented for `()`
+    //~| NOTE this error might have been caused
+    //~| HELP did you intend
 }
 
 fn main() {

src/test/ui/never_type/defaulted-never-note.stderr

@@ -7,7 +7,9 @@ LL | fn foo<T: ImplementedForUnitButNotNever>(_t: T) {}
 LL |     foo(_x);
    |     ^^^ the trait `ImplementedForUnitButNotNever` is not implemented for `!`
    |
-   = note: the trait is implemented for `()`. Possibly this error has been caused by changes to Rust's type-inference algorithm (see issue #48950 <https://github.com/rust-lang/rust/issues/48950> for more information). Consider whether you meant to use the type `()` here instead.
+   = note: this trait is implemented for `()`.
+   = note: this error might have been caused by changes to Rust's type-inference algorithm (see issue #48950 <https://github.com/rust-lang/rust/issues/48950> for more information).
+   = help: did you intend to use the type `()` here instead?
 
 error: aborting due to previous error