[cxx-interop] Do not crash when emitting layout of std::string
#81844
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lib/IRGen/GenStruct.cpp
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| auto fieldTypeSize = ClangContext.getTypeSizeInChars(clangField->getType()); | ||
| auto fieldSize = isZeroSized | ||
| ? clang::CharUnits::Zero() | ||
| : dataSize.value_or(Size(fieldTypeSize.getQuantity())); |
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What are the types involved here? Do we need to wrap fieldTypeSize.getQuantity() in Size?
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Size is a type from the Swift codebase, and fieldTypeSize is coming from Clang, so these are different types.
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Yeah, what confuses me is that the other branch of the expression is clang::CharUnits::Zero(). So what type does fieldSize end up having?
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Ah, I see what you mean. Yeah, let me simplify the types here.
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fieldSize is clang::CharUnits, which swift::Size implicitly converts to.
If a `[[no_unique_address]]` field has zero size according to Clang, and field has a type that isn't representable in Swift, Swift would previously try to add an opaque field of size 1 for it. This is wrong and was causing crashes for `std::string` while emitting a padding field: ``` _LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T1> _LIBCPP_CONCAT3(__padding1_, __LINE__, _); ``` rdar://151941799
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If a
[[no_unique_address]]field has zero size according to Clang, and field has a type that isn't representable in Swift, Swift would previously try to add an opaque field of size 1 for it.This is wrong and was causing crashes for
std::stringwhile emitting a padding field:rdar://151941799