Anonymize binders in tail call sig

Author: compiler-errors

compiler/rustc_mir_build/src/check_tail_calls.rs

@@ -63,6 +63,10 @@ impl<'tcx> TailCallCkVisitor<'_, 'tcx> {
                 "`become` outside of functions should have been disallowed by hit_typeck"
             )
         };
+        // While the `caller_sig` does have its regions erased, it does not have its
+        // binders anonymized. We call `erase_regions` once again to anonymize any binders
+        // within the signature, such as in function pointer or `dyn Trait` args.
+        let caller_sig = self.tcx.erase_regions(caller_sig);
 
         let ExprKind::Scope { value, .. } = call.kind else {
             span_bug!(call.span, "expected scope, found: {call:?}")

tests/ui/explicit-tail-calls/higher-ranked-arg.rs

@@ -0,0 +1,13 @@
+// Regression test for <https://github.com/rust-lang/rust/issues/144826>.
+//@ check-pass
+
+#![feature(explicit_tail_calls)]
+//~^ WARN the feature `explicit_tail_calls` is incomplete
+
+fn foo(x: fn(&i32)) {
+    become bar(x);
+}
+
+fn bar(_: fn(&i32)) {}
+
+fn main() {}

tests/ui/explicit-tail-calls/higher-ranked-arg.stderr

@@ -0,0 +1,11 @@
+warning: the feature `explicit_tail_calls` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/higher-ranked-arg.rs:4:12
+   |
+LL | #![feature(explicit_tail_calls)]
+   |            ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #112788 <https://github.com/rust-lang/rust/issues/112788> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+warning: 1 warning emitted
+