diff options
4 files changed, 46 insertions, 2 deletions
diff --git a/compiler/rustc_mir/src/borrow_check/region_infer/mod.rs b/compiler/rustc_mir/src/borrow_check/region_infer/mod.rs index 3586be2804d..9d45f6fd0d3 100644 --- a/compiler/rustc_mir/src/borrow_check/region_infer/mod.rs +++ b/compiler/rustc_mir/src/borrow_check/region_infer/mod.rs @@ -1145,8 +1145,24 @@ impl<'tcx> RegionInferenceContext<'tcx> { for ur in self.scc_values.universal_regions_outlived_by(r_scc) { let new_lub = self.universal_region_relations.postdom_upper_bound(lub, ur); debug!("approx_universal_upper_bound: ur={:?} lub={:?} new_lub={:?}", ur, lub, new_lub); + // The upper bound of two non-static regions is static: this + // means we know nothing about the relationship between these + // two regions. Pick a 'better' one to use when constructing + // a diagnostic if ur != static_r && lub != static_r && new_lub == static_r { - lub = std::cmp::min(ur, lub); + // Prefer the region with an `external_name` - this + // indicates that the region is early-bound, so working with + // it can produce a nicer error. + if self.region_definition(ur).external_name.is_some() { + lub = ur; + } else if self.region_definition(lub).external_name.is_some() { + // Leave lub unchanged + } else { + // If we get here, we don't have any reason to prefer + // one region over the other. Just pick the + // one with the lower index for now. + lub = std::cmp::min(ur, lub); + } } else { lub = new_lub; } diff --git a/src/test/ui/async-await/issue-74072-lifetime-name-annotations.stderr b/src/test/ui/async-await/issue-74072-lifetime-name-annotations.stderr index 123c3192cff..b96cab9f0f5 100644 --- a/src/test/ui/async-await/issue-74072-lifetime-name-annotations.stderr +++ b/src/test/ui/async-await/issue-74072-lifetime-name-annotations.stderr @@ -2,7 +2,7 @@ error[E0506]: cannot assign to `*x` because it is borrowed --> $DIR/issue-74072-lifetime-name-annotations.rs:9:5 | LL | pub async fn async_fn(x: &mut i32) -> &i32 { - | - let's call the lifetime of this reference `'1` + | - let's call the lifetime of this reference `'1` LL | let y = &*x; | --- borrow of `*x` occurs here LL | *x += 1; diff --git a/src/test/ui/async-await/issue-75785-confusing-named-region.rs b/src/test/ui/async-await/issue-75785-confusing-named-region.rs new file mode 100644 index 00000000000..452614087be --- /dev/null +++ b/src/test/ui/async-await/issue-75785-confusing-named-region.rs @@ -0,0 +1,13 @@ +// edition:2018 +// +// Regression test for issue #75785 +// Tests that we don't point to a confusing named +// region when emitting a diagnostic + +pub async fn async_fn(x: &mut i32) -> (&i32, &i32) { + let y = &*x; + *x += 1; //~ ERROR cannot assign to + (&32, y) +} + +fn main() {} diff --git a/src/test/ui/async-await/issue-75785-confusing-named-region.stderr b/src/test/ui/async-await/issue-75785-confusing-named-region.stderr new file mode 100644 index 00000000000..3b731d9c60a --- /dev/null +++ b/src/test/ui/async-await/issue-75785-confusing-named-region.stderr @@ -0,0 +1,15 @@ +error[E0506]: cannot assign to `*x` because it is borrowed + --> $DIR/issue-75785-confusing-named-region.rs:9:5 + | +LL | pub async fn async_fn(x: &mut i32) -> (&i32, &i32) { + | - let's call the lifetime of this reference `'1` +LL | let y = &*x; + | --- borrow of `*x` occurs here +LL | *x += 1; + | ^^^^^^^ assignment to borrowed `*x` occurs here +LL | (&32, y) + | -------- returning this value requires that `*x` is borrowed for `'1` + +error: aborting due to previous error + +For more information about this error, try `rustc --explain E0506`. |