From 64d98f8ee037282c35007b64c2649055c56af1db Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Wed, 17 Apr 2024 14:19:03 +0200
Subject: Merging upstream version 1.68.2+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 .../propagate-approximated-ref.rs                  | 50 ++++++++++++++++++++++
 1 file changed, 50 insertions(+)
 create mode 100644 tests/ui/nll/closure-requirements/propagate-approximated-ref.rs

(limited to 'tests/ui/nll/closure-requirements/propagate-approximated-ref.rs')

diff --git a/tests/ui/nll/closure-requirements/propagate-approximated-ref.rs b/tests/ui/nll/closure-requirements/propagate-approximated-ref.rs
new file mode 100644
index 000000000..7291c6e97
--- /dev/null
+++ b/tests/ui/nll/closure-requirements/propagate-approximated-ref.rs
@@ -0,0 +1,50 @@
+// Rather convoluted setup where we infer a relationship between two
+// free regions in the closure signature (`'a` and `'b`) on the basis
+// of a relationship between two bound regions (`'x` and `'y`).
+//
+// The idea is that, thanks to invoking `demand_y`, `'x: 'y` must
+// hold, where `'x` and `'y` are bound regions. The closure can't
+// prove that directly, and because `'x` and `'y` are bound it cannot
+// ask the caller to prove it either. But it has bounds on `'x` and
+// `'y` in terms of `'a` and `'b`, and it can propagate a relationship
+// between `'a` and `'b` to the caller.
+//
+// Note: the use of `Cell` here is to introduce invariance. One less
+// variable.
+
+// compile-flags:-Zverbose
+
+#![feature(rustc_attrs)]
+
+use std::cell::Cell;
+
+// Callee knows that:
+//
+// 'x: 'a
+// 'b: 'y
+//
+// so if we are going to ensure that `'x: 'y`, then `'a: 'b` must
+// hold.
+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<&'a &'x u32>, // shows that 'x: 'a
+        &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 lifetime may not live long enough
+    });
+}
+
+fn main() {}
-- 
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