test approximations of the "shorter side" that resort to 'static

This includes the additional case suggested by arielb1.

Author: nikomatsakis

src/test/ui/nll/closure-requirements/propagate-approximated-to-static.rs renamed to src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-no-bound.rs

@@ -8,8 +8,13 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// Test a case where we are forced to approximate one end-point with
-// `'static`. Note that `'static` shows up in the stderr output as `'0`.
+// Test a case where we are trying to prove `'x: 'y` and are forced to
+// approximate the shorter end-point (`'y`) to with `'static`. This is
+// because `'y` is higher-ranked but we know of no relations to other
+// regions. Note that `'static` shows up in the stderr output as `'0`.
+//
+// FIXME(#45827) Because of shortcomings in the MIR type checker,
+// these errors are not (yet) reported.
 
 // compile-flags:-Znll -Zborrowck=mir -Zverbose
 

src/test/ui/nll/closure-requirements/propagate-approximated-to-static.stderr renamed to src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-no-bound.stderr

@@ -1,36 +1,36 @@
 warning: not reporting region error due to -Znll
-  --> $DIR/propagate-approximated-to-static.rs:42:9
+  --> $DIR/propagate-approximated-shorter-to-static-no-bound.rs:47:9
    |
-42 |         demand_y(x, y, x.get())
+47 |         demand_y(x, y, x.get())
    |         ^^^^^^^^^^^^^^^^^^^^^^^
 
 note: External requirements
-  --> $DIR/propagate-approximated-to-static.rs:40:47
+  --> $DIR/propagate-approximated-shorter-to-static-no-bound.rs:45:47
    |
-40 |       establish_relationships(&cell_a, &cell_b, |_outlives, x, y| {
+45 |       establish_relationships(&cell_a, &cell_b, |_outlives, x, y| {
    |  _______________________________________________^
-41 | |         // Only works if 'x: 'y:
-42 | |         demand_y(x, y, x.get())
-43 | |     });
+46 | |         // Only works if 'x: 'y:
+47 | |         demand_y(x, y, x.get())
+48 | |     });
    | |_____^
    |
-   = note: defining type: DefId(0/1:18 ~ propagate_approximated_to_static[317d]::supply[0]::{{closure}}[0]) with closure substs [
+   = note: defining type: DefId(0/1:18 ~ propagate_approximated_shorter_to_static_no_bound[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<&'_#1r &ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 's)) u32>, &ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 't0)) std::cell::Cell<&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 's)) u32>, &ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 't1)) std::cell::Cell<&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 't2)) u32>))
            ]
    = note: number of external vids: 2
    = note: where '_#1r: '_#0r
 
 note: No external requirements
-  --> $DIR/propagate-approximated-to-static.rs:39:1
+  --> $DIR/propagate-approximated-shorter-to-static-no-bound.rs:44:1
    |
-39 | / fn supply<'a, 'b>(cell_a: Cell<&'a u32>, cell_b: Cell<&'b u32>) {
-40 | |     establish_relationships(&cell_a, &cell_b, |_outlives, x, y| {
-41 | |         // Only works if 'x: 'y:
-42 | |         demand_y(x, y, x.get())
-43 | |     });
-44 | | }
+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())
+48 | |     });
+49 | | }
    | |_^
    |
-   = note: defining type: DefId(0/0:6 ~ propagate_approximated_to_static[317d]::supply[0]) with substs []
+   = note: defining type: DefId(0/0:6 ~ propagate_approximated_shorter_to_static_no_bound[317d]::supply[0]) with substs []
 

src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-wrong-bound.rs

@@ -0,0 +1,54 @@
+// 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.
+
+// Test a case where we are trying to prove `'x: 'y` and are forced to
+// approximate the shorter end-point (`'y`) to with `'static`. This is
+// because `'y` is higher-ranked but we know of only irrelevant
+// relations to other regions. Note that `'static` shows up in the
+// stderr output as `'0`.
+//
+// FIXME(#45827) Because of shortcomings in the MIR type checker,
+// these errors are not (yet) reported.
+
+// compile-flags:-Znll -Zborrowck=mir -Zverbose
+
+#![feature(rustc_attrs)]
+
+use std::cell::Cell;
+
+// Callee knows that:
+//
+// 'x: 'a
+// 'y: 'b
+//
+// so the only way we can ensure that `'x: 'y` is to show that
+// `'a: 'static`.
+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<&'b &'y u32>, // shows that 'y: 'b
+        &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())
+    });
+}
+
+fn main() {}

src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-wrong-bound.stderr

@@ -0,0 +1,36 @@
+warning: not reporting region error due to -Znll
+  --> $DIR/propagate-approximated-shorter-to-static-wrong-bound.rs:50:9
+   |
+50 |         demand_y(x, y, x.get())
+   |         ^^^^^^^^^^^^^^^^^^^^^^^
+
+note: External requirements
+  --> $DIR/propagate-approximated-shorter-to-static-wrong-bound.rs:48:47
+   |
+48 |       establish_relationships(&cell_a, &cell_b, |_outlives1, _outlives2, x, y| {
+   |  _______________________________________________^
+49 | |         // Only works if 'x: 'y:
+50 | |         demand_y(x, y, x.get())
+51 | |     });
+   | |_____^
+   |
+   = note: defining type: DefId(0/1:18 ~ propagate_approximated_shorter_to_static_wrong_bound[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<&'_#1r &ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 's)) u32>, &ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 't0)) std::cell::Cell<&'_#2r &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>, &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: where '_#1r: '_#0r
+
+note: No external requirements
+  --> $DIR/propagate-approximated-shorter-to-static-wrong-bound.rs:47:1
+   |
+47 | / fn supply<'a, 'b>(cell_a: Cell<&'a u32>, cell_b: Cell<&'b u32>) {
+48 | |     establish_relationships(&cell_a, &cell_b, |_outlives1, _outlives2, x, y| {
+49 | |         // Only works if 'x: 'y:
+50 | |         demand_y(x, y, x.get())
+51 | |     });
+52 | | }
+   | |_^
+   |
+   = note: defining type: DefId(0/0:6 ~ propagate_approximated_shorter_to_static_wrong_bound[317d]::supply[0]) with substs []
+