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try_promote_type_test: correctly promote lower_bound 
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6 files changed

+81
-63
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6 files changed

+81
-63
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‎compiler/rustc_borrowck/src/region_infer/mod.rs‎

Lines changed: 17 additions & 36 deletions
Original file line numberDiff line numberDiff line change
@@ -973,7 +973,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
973973
propagated_outlives_requirements: &mut Vec<ClosureOutlivesRequirement<'tcx>>,
974974
) -> bool {
975975
let tcx = infcx.tcx;
976-
let TypeTest { generic_kind, lower_bound, span: blame_span, ref verify_bound } = *type_test;
976+
let TypeTest { generic_kind, lower_bound, span: blame_span, verify_bound: _ } = *type_test;
977977

978978
let generic_ty = generic_kind.to_ty(tcx);
979979
let Some(subject) = self.try_promote_type_test_subject(infcx, generic_ty) else {
@@ -1008,50 +1008,31 @@ impl<'tcx> RegionInferenceContext<'tcx> {
10081008
return true;
10091009
}
10101010

1011-
// For each region outlived by lower_bound find a non-local,
1012-
// universal region (it may be the same region) and add it to
1013-
// `ClosureOutlivesRequirement`.
1011+
// Add all non-local universal regions which are outlived by
1012+
// `lower_bound` to the `ClosureOutlivesRequirement`.
1013+
//
1014+
// This is slightly too conservative. To show T: '1, given `'2: '1`
1015+
// and `'3: '1` we only need to prove that T: '2 *or* T: '3, but to
1016+
// avoid potential non-determinism we approximate this by requiring
1017+
// T: '1 and T: '2.
1018+
let mut found_candidate = false;
10141019
for ur in self.scc_values.universal_regions_outlived_by(r_scc) {
1015-
debug!("universal_region_outlived_by ur={:?}", ur);
1016-
// Check whether we can already prove that the "subject" outlives `ur`.
1017-
// If so, we don't have to propagate this requirement to our caller.
1018-
//
1019-
// To continue the example from the function, if we are trying to promote
1020-
// a requirement that `T: 'X`, and we know that `'X = '1 + '2` (i.e., the union
1021-
// `'1` and `'2`), then in this loop `ur` will be `'1` (and `'2`). So here
1022-
// we check whether `T: '1` is something we *can* prove. If so, no need
1023-
// to propagate that requirement.
1024-
//
1025-
// This is needed because -- particularly in the case
1026-
// where `ur` is a local bound -- we are sometimes in a
1027-
// position to prove things that our caller cannot. See
1028-
// #53570 for an example.
1029-
if self.eval_verify_bound(infcx, generic_ty, ur, &verify_bound) {
1030-
continue;
1031-
}
1032-
1033-
let non_local_ub = self.universal_region_relations.non_local_upper_bounds(ur);
1034-
debug!(?non_local_ub);
1035-
1036-
// This is slightly too conservative. To show T: '1, given `'2: '1`
1037-
// and `'3: '1` we only need to prove that T: '2 *or* T: '3, but to
1038-
// avoid potential non-determinism we approximate this by requiring
1039-
// T: '1 and T: '2.
1040-
for upper_bound in non_local_ub {
1041-
debug_assert!(self.universal_regions().is_universal_region(upper_bound));
1042-
debug_assert!(!self.universal_regions().is_local_free_region(upper_bound));
1043-
1020+
if !self.universal_regions().is_local_free_region(ur) {
1021+
debug_assert!(!self.universal_regions().is_local_free_region(ur));
10441022
let requirement = ClosureOutlivesRequirement {
10451023
subject,
1046-
outlived_free_region: upper_bound,
1024+
outlived_free_region: ur,
10471025
blame_span,
10481026
category: ConstraintCategory::Boring,
10491027
};
1050-
debug!(?requirement, "adding closure requirement");
1028+
debug!(?requirement, ?ur, "adding closure requirement");
10511029
propagated_outlives_requirements.push(requirement);
1030+
found_candidate = true;
1031+
} else {
1032+
debug!(?ur, "skippiung local universal");
10521033
}
10531034
}
1054-
true
1035+
found_candidate
10551036
}
10561037

10571038
/// When we promote a type test `T: 'r`, we have to replace all region

‎tests/crashes/122704.rs‎

Lines changed: 0 additions & 14 deletions
This file was deleted.

‎tests/ui/nll/closure-requirements/no-non-local-upper-bound.rs‎

Lines changed: 15 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,15 @@
1+
// This previously ICE'd as it failed to find a non-local universal
2+
// region which is outlived by the `lower_bound` of a type outlives
3+
// when promoting closure requirements. Regression test for #122704.
4+
trait IsStatic: 'static {}
5+
6+
impl<T: 'static> IsStatic for T {}
7+
8+
fn foo<T>(x: Box<T>) -> Box<dyn for<'a> FnOnce(&'a ()) -> Box<dyn IsStatic + 'a>> {
9+
Box::new(move |_| x)
10+
//~^ ERROR the parameter type `T` may not live long enough
11+
//~| ERROR the parameter type `T` may not live long enough
12+
//~| ERROR the parameter type `T` may not live long enough
13+
}
14+
15+
fn main() {}

‎tests/ui/nll/closure-requirements/no-non-local-upper-bound.stderr‎

Lines changed: 42 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,42 @@
1+
error[E0311]: the parameter type `T` may not live long enough
2+
--> $DIR/no-non-local-upper-bound.rs:9:23
3+
|
4+
LL | Box::new(move |_| x)
5+
| -------- ^ ...so that the type `T` will meet its required lifetime bounds
6+
| |
7+
| the parameter type `T` must be valid for the anonymous lifetime as defined here...
8+
|
9+
= help: consider adding an explicit lifetime bound `T: '_`...
10+
11+
error[E0310]: the parameter type `T` may not live long enough
12+
--> $DIR/no-non-local-upper-bound.rs:9:5
13+
|
14+
LL | Box::new(move |_| x)
15+
| ^^^^^^^^^^^^^^^^^^^^
16+
| |
17+
| the parameter type `T` must be valid for the static lifetime...
18+
| ...so that the type `T` will meet its required lifetime bounds
19+
|
20+
help: consider adding an explicit lifetime bound
21+
|
22+
LL | fn foo<T: 'static>(x: Box<T>) -> Box<dyn for<'a> FnOnce(&'a ()) -> Box<dyn IsStatic + 'a>> {
23+
| +++++++++
24+
25+
error[E0310]: the parameter type `T` may not live long enough
26+
--> $DIR/no-non-local-upper-bound.rs:9:23
27+
|
28+
LL | Box::new(move |_| x)
29+
| ^
30+
| |
31+
| the parameter type `T` must be valid for the static lifetime...
32+
| ...so that the type `T` will meet its required lifetime bounds
33+
|
34+
help: consider adding an explicit lifetime bound
35+
|
36+
LL | fn foo<T: 'static>(x: Box<T>) -> Box<dyn for<'a> FnOnce(&'a ()) -> Box<dyn IsStatic + 'a>> {
37+
| +++++++++
38+
39+
error: aborting due to 3 previous errors
40+
41+
Some errors have detailed explanations: E0310, E0311.
42+
For more information about an error, try `rustc --explain E0310`.

‎tests/ui/nll/ty-outlives/projection-implied-bounds.rs‎

Lines changed: 0 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1,8 +1,6 @@
11
// Test that we can deduce when projections like `T::Item` outlive the
22
// function body. Test that this does not imply that `T: 'a` holds.
33

4-
//@ compile-flags:-Zverbose-internals
5-
64
use std::cell::Cell;
75

86
fn twice<F, T>(mut value: T, mut f: F)

‎tests/ui/nll/ty-outlives/projection-implied-bounds.stderr‎

Lines changed: 7 additions & 11 deletions
Original file line numberDiff line numberDiff line change
@@ -1,17 +1,13 @@
1-
error[E0310]: the parameter type `T` may not live long enough
2-
--> $DIR/projection-implied-bounds.rs:30:36
1+
error[E0311]: the parameter type `T` may not live long enough
2+
--> $DIR/projection-implied-bounds.rs:28:36
33
|
44
LL | twice(value, |value_ref, item| invoke2(value_ref, item));
5-
| ^^^^^^^^^^^^^^^^^^^^^^^^
6-
| |
7-
| the parameter type `T` must be valid for the static lifetime...
8-
| ...so that the type `T` will meet its required lifetime bounds
5+
| ----------------- ^^^^^^^^^^^^^^^^^^^^^^^^ ...so that the type `T` will meet its required lifetime bounds
6+
| |
7+
| the parameter type `T` must be valid for the anonymous lifetime as defined here...
98
|
10-
help: consider adding an explicit lifetime bound
11-
|
12-
LL | fn generic2<T: Iterator + 'static>(value: T) {
13-
| +++++++++
9+
= help: consider adding an explicit lifetime bound `T: '_`...
1410

1511
error: aborting due to 1 previous error
1612

17-
For more information about this error, try `rustc --explain E0310`.
13+
For more information about this error, try `rustc --explain E0311`.

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