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[Clang] Use stable_sort in VerifyDiagnosticsConsumer. (#187827)

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The new code introduced for `-verify-directives` in PR #179835 enforces
that the order of diagnostics matches the order of the directives.
However, before checking this, it sorts the directives by
SourceLocation. Perhaps non-obviously, all directives which appear
inside a single comment are given the same SourceLocation, pointing to
the beginning of the comment. While these are added in order they appear
in the comment, the non-stable std::sort may non-detministically
misorder them. Switching to stable_sort ensures the correct order is
verified.

This was observed as a random test failure on the checks in
clang/test/CXX/drs/cwg25xx.cpp lines 250 and 264, in some builds of
Clang. Note that those lines end in backslashes, and thus, despite
appearances, the directives on the following lines are also within the
same single comment.
This commit is contained in:
James Y Knight 2026-03-21 23:11:29 -04:00 committed by GitHub
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commit 3258d361cb
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clang/lib/Frontend/VerifyDiagnosticConsumer.cpp
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@ -1178,7 +1178,7 @@ static unsigned CheckResultsAreInOrder(DiagnosticsEngine &Diags,
std::vector<const Directive *> Ordered(Unordered.size());
std::transform(Unordered.cbegin(), Unordered.cend(), Ordered.begin(),
[](const std::unique_ptr<Directive> &D) { return &*D; });
std::sort(Ordered.begin(), Ordered.end(), directiveComparator);
std::stable_sort(Ordered.begin(), Ordered.end(), directiveComparator);
return Ordered;
};
std::vector<const Directive *> OrderedErrors = sortDirectives(ED.Errors);