1 files changed, 57 insertions, 0 deletions
diff --git a/src/test/ui/regions/regions-relate-bound-regions-on-closures-to-inference-variables.rs b/src/test/ui/regions/regions-relate-bound-regions-on-closures-to-inference-variables.rs
new file mode 100644
index 000000000..b1bdb813a
--- /dev/null
+++ b/src/test/ui/regions/regions-relate-bound-regions-on-closures-to-inference-variables.rs
@@ -0,0 +1,57 @@
+// run-pass
+#![allow(dead_code)]
+// Test that this fairly specialized, but also reasonable, pattern
+// typechecks. The pattern involves regions bound in closures that
+// wind up related to inference variables.
+//
+// NB. Changes to the region implementations have broken this pattern
+// a few times, but it happens to be used in the compiler so those
+// changes were caught. However, those uses in the compiler could
+// easily get changed or refactored away in the future.
+
+struct Ctxt<'tcx> {
+    x: &'tcx Vec<isize>
+}
+
+struct Foo<'a,'tcx:'a> {
+    cx: &'a Ctxt<'tcx>,
+}
+
+impl<'a,'tcx> Foo<'a,'tcx> {
+    fn bother(&mut self) -> isize {
+        self.elaborate_bounds(Box::new(|this| {
+            // (*) Here: type of `this` is `&'f0 Foo<&'f1, '_2>`,
+            // where `'f0` and `'f1` are fresh, free regions that
+            // result from the bound regions on the closure, and `'2`
+            // is a region inference variable created by the call. Due
+            // to the constraints on the type, we find that `'_2 : 'f1
+            // + 'f2` must hold (and can be assumed by the callee).
+            // Region inference has to do some clever stuff to avoid
+            // inferring `'_2` to be `'static` in this case, because
+            // it is created outside the closure but then related to
+            // regions bound by the closure itself. See the
+            // `region_constraints.rs` file (and the `givens` field, in
+            // particular) for more details.
+            this.foo()
+        }))
+    }
+
+    fn foo(&mut self) -> isize {
+        22
+    }
+
+    fn elaborate_bounds(
+        &mut self,
+        mut mk_cand: Box<dyn for<'b> FnMut(&mut Foo<'b, 'tcx>) -> isize>)
+        -> isize
+    {
+        mk_cand(self)
+    }
+}
+
+fn main() {
+    let v = vec![];
+    let cx = Ctxt { x: &v };
+    let mut foo = Foo { cx: &cx };
+    assert_eq!(foo.bother(), 22); // just so the code is not dead, basically
+}