Test showing previous behavior

tests/mir-opt/build_correct_coerce.main.built.after.mir

@@ -0,0 +1,18 @@
+// MIR for `main` after built
+
+fn main() -> () {
+    let mut _0: ();
+    let _1: for<'a> fn(&'a (), &'a ());
+    scope 1 {
+        debug x => _1;
+    }
+
+    bb0: {
+        StorageLive(_1);
+        _1 = foo as for<'a, 'b> fn(&'a (), &'b ()) (PointerCoercion(ReifyFnPointer));
+        FakeRead(ForLet(None), _1);
+        _0 = const ();
+        StorageDead(_1);
+        return;
+    }
+}

tests/mir-opt/build_correct_coerce.rs

@@ -0,0 +1,12 @@
+// skip-filecheck
+
+// Validate that we record the type of the local for `x` as `for<'a> fn(&'a (), &'a ())`,
+// and not `for<'a, 'b>(&'a (), &'b ())`. We previously did the latter due to a bug in
+// the code that records adjustments in HIR typeck.
+
+fn foo<'a, 'b>(_: &'a (), _: &'b ()) {}
+
+// EMIT_MIR build_correct_coerce.main.built.after.mir
+fn main() {
+    let x = foo as for<'a> fn(&'a (), &'a ());
+}