1 files changed, 46 insertions, 0 deletions
diff --git a/src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-wrong-bounds.rs b/src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-wrong-bounds.rs
new file mode 100644
index 000000000..98be92d1c
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+++ b/src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-wrong-bounds.rs
@@ -0,0 +1,46 @@
+// Similarly to escape-argument-callee, a test case where the closure
+// requires a relationship between 2 unrelated higher-ranked regions,
+// with no helpful relations between the HRRs and free regions.
+//
+// In this case, the error is reported by the closure itself. This is
+// because it is unable to approximate the higher-ranked region `'x`,
+// as it only knows of regions that `'x` is outlived by, and none that
+// `'x` outlives.
+
+// compile-flags:-Zverbose
+
+#![feature(rustc_attrs)]
+
+use std::cell::Cell;
+
+// Callee knows that:
+//
+// 'a: 'x
+// 'b: 'y
+//
+// but this doesn't really help us in proving that `'x: 'y`, so
+// closure gets an error.  In particular, we would need to know that
+// `'x: 'a`, so that we could approximate `'x` "downwards" to `'a`.
+fn establish_relationships<'a, 'b, F>(_cell_a: &Cell<&'a u32>, _cell_b: &Cell<&'b u32>, _closure: F)
+where
+    F: for<'x, 'y> FnMut(
+        &Cell<&'x &'a u32>, // shows that 'a: 'x
+        &Cell<&'y &'b u32>, // shows that 'b: 'y
+        &Cell<&'x u32>,
+        &Cell<&'y u32>,
+    ),
+{
+}
+
+fn demand_y<'x, 'y>(_cell_x: &Cell<&'x u32>, _cell_y: &Cell<&'y u32>, _y: &'y u32) {}
+
+#[rustc_regions]
+fn supply<'a, 'b>(cell_a: Cell<&'a u32>, cell_b: Cell<&'b u32>) {
+    establish_relationships(&cell_a, &cell_b, |_outlives1, _outlives2, x, y| {
+        // Only works if 'x: 'y:
+        demand_y(x, y, x.get())
+        //~^ ERROR
+    });
+}
+
+fn main() {}