Auto merge of #56479 - mark-i-m:unsat, r=nikomatsakis

Better lifetime error message

I propose the following error message as more user-friendly

r? @nikomatsakis

Author: bors

src/librustc_mir/borrow_check/nll/region_infer/error_reporting/mod.rs

@@ -505,7 +505,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     ) {
         let mut diag = infcx.tcx.sess.struct_span_err(
             span,
-            "unsatisfied lifetime constraints", // FIXME
+            "lifetime may not live long enough"
         );
 
         let counter = &mut 1;

src/test/ui/nll/closure-requirements/escape-argument-callee.stderr

@@ -9,7 +9,7 @@ LL |         let mut closure = expect_sig(|p, y| *p = y);
                for<'r, 's, 't0> extern "rust-call" fn((&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 'r)) mut &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) i32, &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't0)) i32))
            ]
 
-error: unsatisfied lifetime constraints
+error: lifetime may not live long enough
   --> $DIR/escape-argument-callee.rs:26:45
    |
 LL |         let mut closure = expect_sig(|p, y| *p = y);

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

@@ -16,7 +16,7 @@ LL | |         },
    = note: late-bound region is '_#5r
    = note: late-bound region is '_#6r
 
-error: unsatisfied lifetime constraints
+error: lifetime may not live long enough
   --> $DIR/propagate-approximated-fail-no-postdom.rs:46:13
    |
 LL |         |_outlives1, _outlives2, _outlives3, x, y| {

src/test/ui/nll/closure-requirements/propagate-approximated-ref.rs

@@ -41,10 +41,9 @@ fn demand_y<'x, 'y>(_cell_x: &Cell<&'x u32>, _cell_y: &Cell<&'y u32>, _y: &'y u3
 #[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 unsatisfied lifetime constraints
+        //~^ ERROR lifetime may not live long enough
     });
 }
 

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

@@ -3,10 +3,9 @@ note: External requirements
    |
 LL |       establish_relationships(&cell_a, &cell_b, |_outlives1, _outlives2, x, y| {
    |  _______________________________________________^
-LL | |
 LL | |         // Only works if 'x: 'y:
 LL | |         demand_y(x, y, x.get())
-LL | |         //~^ ERROR unsatisfied lifetime constraints
+LL | |         //~^ ERROR lifetime may not live long enough
 LL | |     });
    | |_____^
    |
@@ -24,17 +23,17 @@ note: No external requirements
    |
 LL | / fn supply<'a, 'b>(cell_a: Cell<&'a u32>, cell_b: Cell<&'b u32>) {
 LL | |     establish_relationships(&cell_a, &cell_b, |_outlives1, _outlives2, x, y| {
-LL | |
 LL | |         // Only works if 'x: 'y:
-...  |
+LL | |         demand_y(x, y, x.get())
+LL | |         //~^ ERROR lifetime may not live long enough
 LL | |     });
 LL | | }
    | |_^
    |
    = note: defining type: DefId(0/0:6 ~ propagate_approximated_ref[317d]::supply[0]) with substs []
 
-error: unsatisfied lifetime constraints
-  --> $DIR/propagate-approximated-ref.rs:46:9
+error: lifetime may not live long enough
+  --> $DIR/propagate-approximated-ref.rs:45:9
    |
 LL | fn supply<'a, 'b>(cell_a: Cell<&'a u32>, cell_b: Cell<&'b u32>) {
    |           --  -- lifetime `'b` defined here

src/test/ui/nll/closure-requirements/propagate-approximated-val.rs

@@ -34,10 +34,9 @@ fn demand_y<'x, 'y>(_outlives1: Cell<&&'x u32>, _outlives2: Cell<&'y &u32>, _y:
 #[rustc_regions]
 fn test<'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(outlives1, outlives2, x.get())
-        //~^ ERROR unsatisfied lifetime constraints
+        //~^ ERROR lifetime may not live long enough
     });
 }
 

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

@@ -3,10 +3,9 @@ note: External requirements
    |
 LL |       establish_relationships(cell_a, cell_b, |outlives1, outlives2, x, y| {
    |  _____________________________________________^
-LL | |
 LL | |         // Only works if 'x: 'y:
 LL | |         demand_y(outlives1, outlives2, x.get())
-LL | |         //~^ ERROR unsatisfied lifetime constraints
+LL | |         //~^ ERROR lifetime may not live long enough
 LL | |     });
    | |_____^
    |
@@ -24,17 +23,17 @@ note: No external requirements
    |
 LL | / fn test<'a, 'b>(cell_a: Cell<&'a u32>, cell_b: Cell<&'b u32>) {
 LL | |     establish_relationships(cell_a, cell_b, |outlives1, outlives2, x, y| {
-LL | |
 LL | |         // Only works if 'x: 'y:
-...  |
+LL | |         demand_y(outlives1, outlives2, x.get())
+LL | |         //~^ ERROR lifetime may not live long enough
 LL | |     });
 LL | | }
    | |_^
    |
    = note: defining type: DefId(0/0:6 ~ propagate_approximated_val[317d]::test[0]) with substs []
 
-error: unsatisfied lifetime constraints
-  --> $DIR/propagate-approximated-val.rs:39:9
+error: lifetime may not live long enough
+  --> $DIR/propagate-approximated-val.rs:38:9
    |
 LL | fn test<'a, 'b>(cell_a: Cell<&'a u32>, cell_b: Cell<&'b u32>) {
    |         --  -- lifetime `'b` defined here

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

@@ -16,7 +16,7 @@ LL | |     });
    = note: late-bound region is '_#2r
    = note: late-bound region is '_#3r
 
-error: unsatisfied lifetime constraints
+error: lifetime may not live long enough
   --> $DIR/propagate-fail-to-approximate-longer-no-bounds.rs:37:9
    |
 LL |     establish_relationships(&cell_a, &cell_b, |_outlives, x, y| {

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

@@ -16,7 +16,7 @@ LL | |     });
    = note: late-bound region is '_#3r
    = note: late-bound region is '_#4r
 
-error: unsatisfied lifetime constraints
+error: lifetime may not live long enough
   --> $DIR/propagate-fail-to-approximate-longer-wrong-bounds.rs:41:9
    |
 LL |     establish_relationships(&cell_a, &cell_b, |_outlives1, _outlives2, x, y| {

src/test/ui/nll/closure-requirements/region-lbr-named-does-not-outlive-static.stderr

@@ -1,4 +1,4 @@
-error: unsatisfied lifetime constraints
+error: lifetime may not live long enough
   --> $DIR/region-lbr-named-does-not-outlive-static.rs:9:5
    |
 LL | fn foo<'a>(x: &'a u32) -> &'static u32 {