test more failure cases for approximating the "longer" side

as suggested by arielb1

Author: nikomatsakis

src/test/ui/nll/closure-requirements/propagate-approximated-to-empty.stderr

@@ -8,8 +8,14 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// Test a case where we fail to approximate one of the regions and
-// hence report an error while checking the closure.
+// 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 knows of no relationships between `'x` and any
+// non-higher-ranked regions.
 
 // compile-flags:-Znll -Zborrowck=mir -Zverbose
 

src/test/ui/nll/closure-requirements/propagate-approximated-to-empty.rs renamed to src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-no-bounds.rs

@@ -0,0 +1,46 @@
+warning: not reporting region error due to -Znll
+  --> $DIR/propagate-fail-to-approximate-longer-no-bounds.rs:47:9
+   |
+47 |         demand_y(x, y, x.get())
+   |         ^^^^^^^^^^^^^^^^^^^^^^^
+
+error: free region `'_#6r` does not outlive free region `'_#4r`
+  --> $DIR/propagate-fail-to-approximate-longer-no-bounds.rs:47:21
+   |
+47 |         demand_y(x, y, x.get())
+   |                     ^
+
+note: External requirements
+  --> $DIR/propagate-fail-to-approximate-longer-no-bounds.rs:45:47
+   |
+45 |       establish_relationships(&cell_a, &cell_b, |_outlives, x, y| {
+   |  _______________________________________________^
+46 | |         // Only works if 'x: 'y:
+47 | |         demand_y(x, y, x.get())
+48 | |         //~^ WARN not reporting region error due to -Znll
+49 | |         //~| ERROR free region `'_#6r` does not outlive free region `'_#4r`
+50 | |     });
+   | |_____^
+   |
+   = note: defining type: DefId(0/1:18 ~ propagate_fail_to_approximate_longer_no_bounds[317d]::supply[0]::{{closure}}[0]) with closure substs [
+               i16,
+               for<'r, 's, 't0, 't1, 't2> extern "rust-call" fn((&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 'r)) std::cell::Cell<&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 's)) &'_#1r u32>, &ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 't0)) std::cell::Cell<&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 't1)) u32>, &ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 't2)) std::cell::Cell<&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 's)) u32>))
+           ]
+   = note: number of external vids: 2
+
+note: No external requirements
+  --> $DIR/propagate-fail-to-approximate-longer-no-bounds.rs:44:1
+   |
+44 | / fn supply<'a, 'b>(cell_a: Cell<&'a u32>, cell_b: Cell<&'b u32>) {
+45 | |     establish_relationships(&cell_a, &cell_b, |_outlives, x, y| {
+46 | |         // Only works if 'x: 'y:
+47 | |         demand_y(x, y, x.get())
+...  |
+50 | |     });
+51 | | }
+   | |_^
+   |
+   = note: defining type: DefId(0/0:6 ~ propagate_fail_to_approximate_longer_no_bounds[317d]::supply[0]) with substs []
+
+error: aborting due to previous error
+

src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-no-bounds.stderr

@@ -0,0 +1,57 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// 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:-Znll -Zborrowck=mir -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())
+        //~^ WARN not reporting region error due to -Znll
+        //~| ERROR free region `'_#5r` does not outlive free region `'_#7r`
+    });
+}
+
+fn main() {}

src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-wrong-bounds.rs

@@ -0,0 +1,46 @@
+warning: not reporting region error due to -Znll
+  --> $DIR/propagate-fail-to-approximate-longer-wrong-bounds.rs:51:9
+   |
+51 |         demand_y(x, y, x.get())
+   |         ^^^^^^^^^^^^^^^^^^^^^^^
+
+error: free region `'_#5r` does not outlive free region `'_#7r`
+  --> $DIR/propagate-fail-to-approximate-longer-wrong-bounds.rs:51:21
+   |
+51 |         demand_y(x, y, x.get())
+   |                     ^
+
+note: External requirements
+  --> $DIR/propagate-fail-to-approximate-longer-wrong-bounds.rs:49:47
+   |
+49 |       establish_relationships(&cell_a, &cell_b, |_outlives1, _outlives2, x, y| {
+   |  _______________________________________________^
+50 | |         // Only works if 'x: 'y:
+51 | |         demand_y(x, y, x.get())
+52 | |         //~^ WARN not reporting region error due to -Znll
+53 | |         //~| ERROR free region `'_#5r` does not outlive free region `'_#7r`
+54 | |     });
+   | |_____^
+   |
+   = note: defining type: DefId(0/1:18 ~ propagate_fail_to_approximate_longer_wrong_bounds[317d]::supply[0]::{{closure}}[0]) with closure substs [
+               i16,
+               for<'r, 's, 't0, 't1, 't2, 't3> extern "rust-call" fn((&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 'r)) std::cell::Cell<&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 's)) &'_#1r u32>, &ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 't0)) std::cell::Cell<&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 't1)) &'_#2r u32>, &ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 't2)) std::cell::Cell<&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 's)) u32>, &ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 't3)) std::cell::Cell<&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 't1)) u32>))
+           ]
+   = note: number of external vids: 3
+
+note: No external requirements
+  --> $DIR/propagate-fail-to-approximate-longer-wrong-bounds.rs:48:1
+   |
+48 | / fn supply<'a, 'b>(cell_a: Cell<&'a u32>, cell_b: Cell<&'b u32>) {
+49 | |     establish_relationships(&cell_a, &cell_b, |_outlives1, _outlives2, x, y| {
+50 | |         // Only works if 'x: 'y:
+51 | |         demand_y(x, y, x.get())
+...  |
+54 | |     });
+55 | | }
+   | |_^
+   |
+   = note: defining type: DefId(0/0:6 ~ propagate_fail_to_approximate_longer_wrong_bounds[317d]::supply[0]) with substs []
+
+error: aborting due to previous error
+