Add regression test for higher-ranked fn pointer trait impl mismatch errors

tests/ui/higher-ranked/hr-fn-ptr-trait-impl-mismatch-29061.rs

@@ -0,0 +1,33 @@
+//! Regression test for <https://github.com/rust-lang/rust/issues/29061>.
+//!
+//! A trait implemented for a higher-ranked fn pointer is not implemented for a fn pointer
+//! with a specific lifetime, and vice versa. The errors now spell out which form the impl
+//! applies to instead of just saying the bound is unsatisfied.
+
+//@ edition: 2024
+
+#![allow(dead_code)]
+
+fn x(_: &()) {}
+
+trait HR {}
+impl HR for fn(&()) {}
+fn hr<T: HR>(_: T) {}
+
+trait NotHR {}
+impl<'a> NotHR for fn(&'a ()) {}
+fn not_hr<T: NotHR>(_: T) {}
+
+fn a<'a>() {
+    let not_hr_func: fn(&'a ()) = x;
+    let hr_func: fn(&()) = x;
+    let hr_func2: for<'b> fn(&'b ()) = x;
+    hr(not_hr_func);
+    //~^ ERROR implementation of `HR` is not general enough
+    not_hr(hr_func);
+    //~^ ERROR implementation of `NotHR` is not general enough
+    not_hr(hr_func2);
+    //~^ ERROR implementation of `NotHR` is not general enough
+}
+
+fn main() {}

tests/ui/higher-ranked/hr-fn-ptr-trait-impl-mismatch-29061.stderr

@@ -0,0 +1,29 @@
+error: implementation of `HR` is not general enough
+  --> $DIR/hr-fn-ptr-trait-impl-mismatch-29061.rs:25:5
+   |
+LL |     hr(not_hr_func);
+   |     ^^^^^^^^^^^^^^^ implementation of `HR` is not general enough
+   |
+   = note: `HR` would have to be implemented for the type `fn(&'0 ())`, for some specific lifetime `'0`...
+   = note: ...but `HR` is actually implemented for the type `for<'a> fn(&'a ())`
+
+error: implementation of `NotHR` is not general enough
+  --> $DIR/hr-fn-ptr-trait-impl-mismatch-29061.rs:27:5
+   |
+LL |     not_hr(hr_func);
+   |     ^^^^^^^^^^^^^^^ implementation of `NotHR` is not general enough
+   |
+   = note: `NotHR` would have to be implemented for the type `for<'a> fn(&'a ())`
+   = note: ...but `NotHR` is actually implemented for the type `fn(&'0 ())`, for some specific lifetime `'0`
+
+error: implementation of `NotHR` is not general enough
+  --> $DIR/hr-fn-ptr-trait-impl-mismatch-29061.rs:29:5
+   |
+LL |     not_hr(hr_func2);
+   |     ^^^^^^^^^^^^^^^^ implementation of `NotHR` is not general enough
+   |
+   = note: `NotHR` would have to be implemented for the type `for<'b> fn(&'b ())`
+   = note: ...but `NotHR` is actually implemented for the type `fn(&'0 ())`, for some specific lifetime `'0`
+
+error: aborting due to 3 previous errors
+