1 files changed, 34 insertions, 0 deletions
diff --git a/src/test/ui/polymorphization/closure_in_upvar/fnmut.rs b/src/test/ui/polymorphization/closure_in_upvar/fnmut.rs
new file mode 100644
index 000000000..62164ff94
--- /dev/null
+++ b/src/test/ui/polymorphization/closure_in_upvar/fnmut.rs
@@ -0,0 +1,34 @@
+// build-pass
+// compile-flags:-Zpolymorphize=on -Csymbol-mangling-version=v0
+
+fn foo(f: impl Fn()) {
+    // Mutate an upvar from `x` so that it implements `FnMut`.
+    let mut outer = 3;
+    let mut x = |_: ()| {
+        outer = 4;
+        ()
+    };
+
+    // Don't use `f` in `y`, but refer to `x` so that the closure substs contain a reference to
+    // `x` that will differ for each instantiation despite polymorphisation of the varying
+    // argument.
+    let mut y = || x(());
+
+    // Consider `f` used in `foo`.
+    f();
+    // Use `y` so that it is visited in monomorphisation collection.
+    y();
+}
+
+fn entry_a() {
+    foo(|| ());
+}
+
+fn entry_b() {
+    foo(|| ());
+}
+
+fn main() {
+    entry_a();
+    entry_b();
+}