Rollup merge of #144835 - compiler-errors:tail-call-sig-binder, r=WaffleLapkin

Anonymize binders in tail call sig

See the comment for explanation

Fixes rust-lang/rust#144826

r? WaffleLapkin

compiler/rustc_mir_build/src/check_tail_calls.rs

@@ -60,9 +60,13 @@ impl<'tcx> TailCallCkVisitor<'_, 'tcx> {
         let BodyTy::Fn(caller_sig) = self.thir.body_type else {
             span_bug!(
                 call.span,
-                "`become` outside of functions should have been disallowed by hit_typeck"
+                "`become` outside of functions should have been disallowed by hir_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)]
+#![expect(incomplete_features)]
+
+fn foo(x: fn(&i32)) {
+    become bar(x);
+}
+
+fn bar(_: fn(&i32)) {}
+
+fn main() {}