bless test about post dominating lower bounds

Author: LorrensP-2158466

tests/ui/nll/closure-requirements/propagate-approximated-fail-no-postdom.rs

@@ -1,5 +1,5 @@
-// Test where we fail to approximate due to demanding a postdom
-// relationship between our upper bounds.
+// Test that we can propagate multiple region errors by propagating all
+// non-local lower bounds of `fr_longer`.
 
 //@ compile-flags:-Zverbose-internals
 
@@ -13,9 +13,8 @@ use std::cell::Cell;
 // 'x: 'b
 // 'c: 'y
 //
-// we have to prove that `'x: 'y`. We currently can only approximate
-// via a postdominator -- hence we fail to choose between `'a` and
-// `'b` here and report the error in the closure.
+// we have to prove that `'x: 'y`. We find non-local lower bounds of 'x to be 'a and 'b and
+// non-local upper bound of 'y to be 'c. So we propagate `'b: 'c` and `'a: 'c`.
 fn establish_relationships<'a, 'b, 'c, F>(
     _cell_a: Cell<&'a u32>,
     _cell_b: Cell<&'b u32>,
@@ -36,14 +35,16 @@ fn demand_y<'x, 'y>(_cell_x: Cell<&'x u32>, _cell_y: Cell<&'y u32>, _y: &'y u32)
 
 #[rustc_regions]
 fn supply<'a, 'b, 'c>(cell_a: Cell<&'a u32>, cell_b: Cell<&'b u32>, cell_c: Cell<&'c u32>) {
+    //~vv ERROR lifetime may not live long enough
+    //~v ERROR lifetime may not live long enough
     establish_relationships(
         cell_a,
         cell_b,
         cell_c,
         |_outlives1, _outlives2, _outlives3, x, y| {
             // Only works if 'x: 'y:
             let p = x.get();
-            demand_y(x, y, p) //~ ERROR
+            demand_y(x, y, p)
         },
     );
 }

tests/ui/nll/closure-requirements/propagate-approximated-fail-no-postdom.stderr

@@ -1,5 +1,5 @@
-note: no external requirements
-  --> $DIR/propagate-approximated-fail-no-postdom.rs:43:9
+note: external requirements
+  --> $DIR/propagate-approximated-fail-no-postdom.rs:44:9
    |
 LL |         |_outlives1, _outlives2, _outlives3, x, y| {
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -14,29 +14,66 @@ LL |         |_outlives1, _outlives2, _outlives3, x, y| {
    = note: late-bound region is '?4
    = note: late-bound region is '?5
    = note: late-bound region is '?6
+   = note: number of external vids: 7
+   = note: where '?2: '?3
+   = note: where '?1: '?3
+
+note: no external requirements
+  --> $DIR/propagate-approximated-fail-no-postdom.rs:37:1
+   |
+LL | fn supply<'a, 'b, 'c>(cell_a: Cell<&'a u32>, cell_b: Cell<&'b u32>, cell_c: Cell<&'c u32>) {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: defining type: supply
 
 error: lifetime may not live long enough
-  --> $DIR/propagate-approximated-fail-no-postdom.rs:46:13
+  --> $DIR/propagate-approximated-fail-no-postdom.rs:40:5
    |
-LL |         |_outlives1, _outlives2, _outlives3, x, y| {
-   |          ----------              ---------- has type `Cell<&'2 &'?3 u32>`
-   |          |
-   |          has type `Cell<&'?1 &'1 u32>`
+LL |   fn supply<'a, 'b, 'c>(cell_a: Cell<&'a u32>, cell_b: Cell<&'b u32>, cell_c: Cell<&'c u32>) {
+   |             --      -- lifetime `'c` defined here
+   |             |
+   |             lifetime `'a` defined here
 ...
-LL |             demand_y(x, y, p)
-   |             ^^^^^^^^^^^^^^^^^ argument requires that `'1` must outlive `'2`
+LL | /     establish_relationships(
+LL | |         cell_a,
+LL | |         cell_b,
+LL | |         cell_c,
+...  |
+LL | |         },
+LL | |     );
+   | |_____^ argument requires that `'a` must outlive `'c`
    |
-   = note: requirement occurs because of the type `Cell<&'?34 u32>`, which makes the generic argument `&'?34 u32` invariant
+   = help: consider adding the following bound: `'a: 'c`
+   = note: requirement occurs because of the type `Cell<&'?10 u32>`, which makes the generic argument `&'?10 u32` invariant
    = note: the struct `Cell<T>` is invariant over the parameter `T`
    = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
 
-note: no external requirements
-  --> $DIR/propagate-approximated-fail-no-postdom.rs:38:1
+error: lifetime may not live long enough
+  --> $DIR/propagate-approximated-fail-no-postdom.rs:40:5
    |
-LL | fn supply<'a, 'b, 'c>(cell_a: Cell<&'a u32>, cell_b: Cell<&'b u32>, cell_c: Cell<&'c u32>) {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |   fn supply<'a, 'b, 'c>(cell_a: Cell<&'a u32>, cell_b: Cell<&'b u32>, cell_c: Cell<&'c u32>) {
+   |                 --  -- lifetime `'c` defined here
+   |                 |
+   |                 lifetime `'b` defined here
+...
+LL | /     establish_relationships(
+LL | |         cell_a,
+LL | |         cell_b,
+LL | |         cell_c,
+...  |
+LL | |         },
+LL | |     );
+   | |_____^ argument requires that `'b` must outlive `'c`
    |
-   = note: defining type: supply
+   = help: consider adding the following bound: `'b: 'c`
+   = note: requirement occurs because of the type `Cell<&'?10 u32>`, which makes the generic argument `&'?10 u32` invariant
+   = note: the struct `Cell<T>` is invariant over the parameter `T`
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
+
+help: the following changes may resolve your lifetime errors
+   |
+   = help: add bound `'a: 'c`
+   = help: add bound `'b: 'c`
 
-error: aborting due to 1 previous error
+error: aborting due to 2 previous errors