1 files changed, 40 insertions, 0 deletions
diff --git a/src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-comparing-against-free.rs b/src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-comparing-against-free.rs
new file mode 100644
index 000000000..afe6f10a5
--- /dev/null
+++ b/src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-comparing-against-free.rs
@@ -0,0 +1,40 @@
+// Test a case where we setup relationships like `'x: 'a` or `'a: 'x`,
+// where `'x` is bound in closure type but `'a` is free. This forces
+// us to approximate `'x` one way or the other.
+
+// compile-flags:-Zverbose
+
+#![feature(rustc_attrs)]
+
+use std::cell::Cell;
+
+fn foo<'a, F>(_cell: Cell<&'a u32>, _f: F)
+where
+    F: for<'x> FnOnce(Cell<&'a u32>, Cell<&'x u32>),
+{
+}
+
+#[rustc_regions]
+fn case1() {
+    let a = 0;
+    let cell = Cell::new(&a);
+    foo(cell, |cell_a, cell_x| {
+        cell_a.set(cell_x.get()); // forces 'x: 'a, error in closure
+        //~^ ERROR
+    })
+}
+
+#[rustc_regions]
+fn case2() {
+    let a = 0;
+    let cell = Cell::new(&a);
+    //~^ ERROR `a` does not live long enough
+
+    // As you can see in the stderr output, this closure propoagates a
+    // requirement that `'a: 'static'.
+    foo(cell, |cell_a, cell_x| {
+        cell_x.set(cell_a.get()); // forces 'a: 'x, implies 'a = 'static -> borrow error
+    })
+}
+
+fn main() { }