Add regression test for #74400

src/test/ui/lifetimes/lifetime-errors/issue_74400.nll.stderr

@@ -0,0 +1,30 @@
+error[E0310]: the parameter type `T` may not live long enough
+  --> $DIR/issue_74400.rs:12:5
+   |
+LL |     f(data, identity)
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = help: consider adding an explicit lifetime bound `T: 'static`...
+
+error[E0308]: mismatched types
+  --> $DIR/issue_74400.rs:12:5
+   |
+LL |     f(data, identity)
+   |     ^^^^^^^^^^^^^^^^^ one type is more general than the other
+   |
+   = note: expected type `for<'r> Fn<(&'r T,)>`
+              found type `Fn<(&T,)>`
+
+error: implementation of `FnOnce` is not general enough
+  --> $DIR/issue_74400.rs:12:5
+   |
+LL |     f(data, identity)
+   |     ^^^^^^^^^^^^^^^^^ implementation of `FnOnce` is not general enough
+   |
+   = note: `fn(&'2 T) -> &'2 T {identity::<&'2 T>}` must implement `FnOnce<(&'1 T,)>`, for any lifetime `'1`...
+   = note: ...but it actually implements `FnOnce<(&'2 T,)>`, for some specific lifetime `'2`
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0308, E0310.
+For more information about an error, try `rustc --explain E0308`.

src/test/ui/lifetimes/lifetime-errors/issue_74400.rs

@@ -0,0 +1,13 @@
+//! Regression test for #74400: Type mismatch in function arguments E0631, E0271 are falsely
+//! recognized as E0308 mismatched types.
+
+use std::convert::identity;
+
+fn main() {}
+
+fn f<T, S>(data: &[T], key: impl Fn(&T) -> S) {
+}
+
+fn g<T>(data: &[T]) {
+    f(data, identity) //~ ERROR implementation of `FnOnce` is not general
+}

src/test/ui/lifetimes/lifetime-errors/issue_74400.stderr

@@ -0,0 +1,11 @@
+error: implementation of `FnOnce` is not general enough
+  --> $DIR/issue_74400.rs:12:5
+   |
+LL |     f(data, identity)
+   |     ^ implementation of `FnOnce` is not general enough
+   |
+   = note: `fn(&'2 T) -> &'2 T {identity::<&'2 T>}` must implement `FnOnce<(&'1 T,)>`, for any lifetime `'1`...
+   = note: ...but it actually implements `FnOnce<(&'2 T,)>`, for some specific lifetime `'2`
+
+error: aborting due to previous error
+