fixed diagnostic

Author: Kivooeo

compiler/rustc_mir_build/src/check_tail_calls.rs

@@ -132,7 +132,11 @@ impl<'tcx> TailCallCkVisitor<'_, 'tcx> {
 
         if caller_sig.inputs_and_output != callee_sig.inputs_and_output {
             if caller_sig.inputs() != callee_sig.inputs() {
-                self.report_arguments_mismatch(expr.span, caller_sig, callee_sig);
+                self.report_arguments_mismatch(
+                    expr.span,
+                    self.caller_ty.fn_sig(self.tcx).skip_binder(),
+                    callee_sig,
+                );
             }
 
             // FIXME(explicit_tail_calls): this currently fails for cases where opaques are used.

tests/ui/explicit-tail-calls/caller-lifetime-presence.rs

@@ -0,0 +1,29 @@
+//! Regression test for: https://github.com/rust-lang/rust/issues/144957
+//!
+//! Once upon a time, the compiler decided lifetimes weren’t important enough to show in diagnostics
+//! That decision did not go well. This test ensures we don’t repeat that mistake.
+//!
+//! Specifically: we’re checking that the `become` call produces an error
+//! **with** lifetimes preserved
+//! in both caller and callee signatures. Otherwise, good luck figuring out what went wrong.
+//!
+//! If this test fails:
+//! - Either lifetimes are being omitted from the diagnostic again (bad, fix it),
+//! - Or the message format changed (okay, update the test).
+
+#![feature(explicit_tail_calls)]
+#![allow(incomplete_features)]
+
+fn foo<'a>(_: fn(&'a ())) {
+    become bar(dummy);
+    //~^ ERROR mismatched signatures
+    //~| NOTE `become` requires caller and callee to have matching signatures
+    //~| NOTE caller signature: `fn(fn(&'a ()))`
+    //~| NOTE callee signature: `fn(for<'a> fn(&'a ()))`
+}
+
+fn bar(_: fn(&())) {}
+
+fn dummy(_: &()) {}
+
+fn main() {}

tests/ui/explicit-tail-calls/caller-lifetime-presence.stderr

@@ -0,0 +1,12 @@
+error: mismatched signatures
+  --> $DIR/caller-lifetime-presence.rs:18:5
+   |
+LL |     become bar(dummy);
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: `become` requires caller and callee to have matching signatures
+   = note: caller signature: `fn(fn(&'a ()))`
+   = note: callee signature: `fn(for<'a> fn(&'a ()))`
+
+error: aborting due to 1 previous error
+