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Note specific regions involved in 'borrowed data escapes' error

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Fixes #67007

Currently, a 'borrowed data escapes' error does not mention
the specific lifetime involved (except indirectly through a suggestion
about adding a lifetime bound). We now explain the specific lifetime
relationship that failed to hold, which improves otherwise vague
error messages.
This commit is contained in:
Aaron Hill 2021-10-03 15:25:26 -05:00
parent 25ec827385
commit 3c974adb4c
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GPG key ID: B4087E510E98B164
18 changed files with 209 additions and 39 deletions
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21
compiler/rustc_borrowck/src/diagnostics/region_errors.rs
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@ -498,6 +498,27 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
diag.span_label(*span, format!("`{}` escapes the {} body here", fr_name, escapes_from));
}
// Only show an extra note if we can find an 'error region' for both of the region
// variables. This avoids showing a noisy note that just mentions 'synthetic' regions
// that don't help the user understand the error.
if self.to_error_region(errci.fr).is_some()
&& self.to_error_region(errci.outlived_fr).is_some()
{
let fr_region_name = self.give_region_a_name(errci.fr).unwrap();
fr_region_name.highlight_region_name(&mut diag);
let outlived_fr_region_name = self.give_region_a_name(errci.outlived_fr).unwrap();
outlived_fr_region_name.highlight_region_name(&mut diag);
diag.span_label(
*span,
format!(
"{}requires that `{}` must outlive `{}`",
category.description(),
fr_region_name,
outlived_fr_region_name,
),
);
}
diag
}