1 files changed, 57 insertions, 0 deletions
diff --git a/src/test/ui/unboxed-closures/unboxed-closures-mutate-upvar.rs b/src/test/ui/unboxed-closures/unboxed-closures-mutate-upvar.rs
new file mode 100644
index 000000000..57e6d3065
--- /dev/null
+++ b/src/test/ui/unboxed-closures/unboxed-closures-mutate-upvar.rs
@@ -0,0 +1,57 @@
+// Test that we cannot mutate an outer variable that is not declared
+// as `mut` through a closure. Also test that we CAN mutate a moved copy,
+// unless this is a `Fn` closure. Issue #16749.
+
+#![feature(unboxed_closures)]
+
+use std::mem;
+
+fn to_fn<A,F:Fn<A>>(f: F) -> F { f }
+fn to_fn_mut<A,F:FnMut<A>>(f: F) -> F { f }
+
+fn a() {
+    let n = 0;
+    let mut f = to_fn_mut(|| {
+        n += 1; //~ ERROR cannot assign to `n`, as it is not declared as mutable
+    });
+}
+
+fn b() {
+    let mut n = 0;
+    let mut f = to_fn_mut(|| {
+        n += 1; // OK
+    });
+}
+
+fn c() {
+    let n = 0;
+    let mut f = to_fn_mut(move || {
+        // If we just did a straight-forward desugaring, this would
+        // compile, but we do something a bit more subtle, and hence
+        // we get an error.
+        n += 1; //~ ERROR cannot assign
+    });
+}
+
+fn d() {
+    let mut n = 0;
+    let mut f = to_fn_mut(move || {
+        n += 1; // OK
+    });
+}
+
+fn e() {
+    let n = 0;
+    let mut f = to_fn(move || {
+        n += 1; //~ ERROR cannot assign
+    });
+}
+
+fn f() {
+    let mut n = 0;
+    let mut f = to_fn(move || {
+        n += 1; //~ ERROR cannot assign
+    });
+}
+
+fn main() { }