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coverage: Fix an unstable-sort inconsistency in coverage spans

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This code was calling `sort_unstable_by`, but failed to impose a total order on
the initial spans. That resulted in unpredictable handling of closure spans,
producing inconsistencies in the coverage maps and in user-visible coverage
reports.

This patch fixes the problem by always sorting closure spans before
otherwise-identical non-closure spans, and also switches to a stable sort in
case the ordering is still not total.
This commit is contained in:
Zalathar 2023-09-18 21:11:14 +10:00
parent 078eb1120a
commit 4690f97099
4 changed files with 20 additions and 17 deletions
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5
compiler/rustc_mir_transform/src/coverage/spans.rs
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@ -333,7 +333,7 @@ impl<'a, 'tcx> CoverageSpans<'a, 'tcx> {
initial_spans.push(CoverageSpan::for_fn_sig(self.fn_sig_span));
initial_spans.sort_unstable_by(|a, b| {
initial_spans.sort_by(|a, b| {
if a.span.lo() == b.span.lo() {
if a.span.hi() == b.span.hi() {
if a.is_in_same_bcb(b) {
@ -357,6 +357,9 @@ impl<'a, 'tcx> CoverageSpans<'a, 'tcx> {
a.span.lo().partial_cmp(&b.span.lo())
}
.unwrap()
// If two spans are otherwise identical, put closure spans first,
// as this seems to be what the refinement step expects.
.then_with(|| Ord::cmp(&a.is_closure, &b.is_closure).reverse())
});
initial_spans