[ClangImporter] Do not import enum when already imported via DeclContext #85424
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j-hui
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hnrklssn
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lib/ClangImporter/ImportDecl.cpp
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| if (!HadForwardDeclaration) { | ||
| auto it = ImportedDecls.try_emplace({Canon, version}, Result); | ||
| if (!it.second && Result != it.first->second) { | ||
| ABORT([&](auto &out) { |
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nice, didn't know about this macro
hnrklssn
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Nov 11, 2025
lib/ClangImporter/ImportDecl.cpp
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| Canon->getSourceRange().print(out, Instance->getSourceManager()); | ||
| } | ||
| out << "\nImported as Swift Decl:\n"; | ||
| Result->dump(out, 4); |
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there's an indentation parameter to dump?? is that true for all of them or just decls?
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Appears to be available for all swift::Decls
hnrklssn
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Nov 11, 2025
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It works 🥳 |
Before we import an enum, we import its DeclContext. If that DeclContext
gets resolved to a struct that contains that field of that enum type,
e.g.:
typedef CF_OPTIONS(uint32_t, MyFlags) {
...
} CF_SWIFT_NAME(MyCtx.Flags);
struct MyStruct {
MyFlags flags;
...
} CF_SWIFT_NAME(MyCtx);
We end up with a cycle, i.e., MyFlags -> MyCtx -> MyStruct -> MyFlags.
Existing cycle-breaking mechanisms seem to prevent this from looping
infinitely, but it leads to us importing two copies of the enum, which
can cause errors later during CodeGen.
This patch breaks the cycle by checking the cache again.
N.B. as of this commit, the circular-import-as-member.swift test doesn't
actually fail *without* the fix, because ClangImporter is quite
lenient about importing the same clang::Decl multiple times. An earlier
attempt at this patch ABORT()'d the compiler as soon as a duplicate is
detected, but that led to more isseus beyond the scope of this patch.
rdar://162317760
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If we try to import this in ObjC interop mode:
ClangImporter tries to import
MyCtx/MyStructbefore it importsMyFlags(viaimportDeclContextOf()), which in turn tries to importMyFlagsagain due to theflagsfield. The existing cycle-breaking mechanism prevents us from looping infinitely, but leads us to import two copies of the SwiftEnumDecl, which can cause errors later during CodeGen.This patch adds an assertion to catch such issues earlier, and breaks the cycle by checking the cache again.This patch no longer does so because that caused issues beyond the scope of this patch.rdar://162317760