[cxx-interop] Mark some zero-sized value types as unavailable #77100
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Xazax-hun
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| std::optional<std::function<bool(const NominalTypeDecl *)>> isZeroSized = | ||
| std::nullopt); |
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Is it reasonable to invoke this without passing a zero-size check in some cases? Wondering if the default value of the parameter is needed here.
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Unfortunately, there is one user in the Swift AST that checks for the correct use of @_expose(Cxx). We do not have access to the type layout in that module, so we cannot do this check when doing semantic analysis for this attribute. I added the default argument for that user. We would still diagnose zero sized types as unavailable, but would do during the interop header generation via an unavailable attribe (not via a diagnostic while doing the semantic analysis for @expose).
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I don't feel strongly, but could we remove the default value on the declaration, and pass nullopt on that call site, since that seems to be an exception that we wouldn't want to be repeated elsewhere?
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Ah, good point! Will do.
Currently, we do not support exporting zero-sized value types from Swift to C++. It needs some work on our end as these types are not part of the lowered signature. In the meantime, this PR makes sure that common (but not all) zero sized types are properly marked as unavailable. This is important as the proper diagnostic will give users a hint how to work around this problem. Moreover, it is really easy to hit this when someone is experimenting with interop, so it is important to not have a cryptic failure mode. rdar://138122545
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Currently, we do not support exporting zero-sized value types from Swift to C++. It needs some work on our end as these types are not part of the lowered signature. In the meantime, this PR makes sure that common (but not all) zero sized types are properly marked as unavailable. This is important as the proper diagnostic will give users a hint how to work around this problem. Moreover, it is really easy to hit this when someone is experimenting with interop, so it is important to not have a cryptic failure mode.
rdar://138122545