diff options
| author | Aaron Hill <aa1ronham@gmail.com> | 2020-10-20 16:31:54 -0400 |
|---|---|---|
| committer | Aaron Hill <aa1ronham@gmail.com> | 2020-12-17 13:24:40 -0500 |
| commit | 419d3ae02849d47899f8fc221d37b05ac24f4efd (patch) | |
| tree | 74e550e80e64fc42f648ff447086a03c0b870b8d /src | |
| parent | d23e08448332425a84ae23124bea4dbd685536ce (diff) | |
Prefer regions with an `external_name` in `approx_universal_upper_bound`
Fixes #75785 When displaying a MIR borrowcheck error, we may need to find an upper bound for a region, which gives us a region to point to in the error message. However, a region might outlive multiple distinct universal regions, in which case the only upper bound is 'static To try to display a meaningful error message, we compute an 'approximate' upper bound by picking one of the universal regions. Currently, we pick the region with the lowest index - however, this caused us to produce a suboptimal error message in issue #75785 This PR `approx_universal_upper_bound` to prefer regions with an `external_name`. This causes us to prefer regions from function arguments/upvars, which seems to lead to a nicer error message in some cases.
Diffstat (limited to 'src')
3 files changed, 29 insertions, 1 deletions
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`. |