[ClangImporter] Import C++ subscript overloads in stable order#89478
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airspeedswift wants to merge 1 commit into
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[ClangImporter] Import C++ subscript overloads in stable order#89478airspeedswift wants to merge 1 commit into
airspeedswift wants to merge 1 commit into
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`lookupAndImportSubscripts` grouped operator[] overloads in a SmallDenseMap keyed by CXXOverloadArgTypes, whose hash is built from clang::QualType opaque pointers. ASLR makes those pointer values vary across runs, so iteration order over the map varies too — and that order determined the order of subscripts added to the imported Swift struct. Downstream, that fed the constraint solver's overload set in varying order; for cases with multiple equally-ranked viable candidates, *which one wins* could change run-to-run. Switch to SmallMapVector so iteration follows insertion order. The hash-keyed lookup that groups same-arg-type getters/setters is preserved; only iteration becomes deterministic. Concrete repro: typechecking test/Interop/Cxx/operators/subscript-overloads-typechecker.swift 20 times produced 3 distinct outputs before this change and 1 afterwards.
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@swift-ci please smoke test |
j-hui
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May 27, 2026
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Oof, thanks for catching this!
Out of curiosity, how did this manifest elsewhere/outside of that test?
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I was trying to fix diagnostics like this and the tests for the fix were failing because the results varied run to run. That would mean if there were multiple diagnostics, the order would change (including the top one Xcode shows) unless we sorted them. |
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lookupAndImportSubscriptsgrouped operator[] overloads in a SmallDenseMap keyed by CXXOverloadArgTypes, whose hash is built from clang::QualType opaque pointers. ASLR makes those pointer values vary across runs, so iteration order over the map varies too — and that order determined the order of subscripts added to the imported Swift struct. Downstream, that fed the constraint solver's overload set in varying order; for cases with multiple equally-ranked viable candidates, which one wins could change run-to-run.Switch to SmallMapVector so iteration follows insertion order. The hash-keyed lookup that groups same-arg-type getters/setters is preserved; only iteration becomes deterministic.
Concrete repro: typechecking
test/Interop/Cxx/operators/subscript-overloads-typechecker.swift 20 times produced 3 distinct outputs before this change and 1 afterwards.