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[clang-doc] concatenate SymbolIDs to truncated mangled names #159490

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merged 1 commit into from
Sep 23, 2025
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[clang-doc] concatenate SymbolIDs to truncated mangled names #159490

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10 changes: 4 additions & 6 deletions clang-tools-extra/clang-doc/Serialize.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -780,12 +780,10 @@ static void populateSymbolInfo(SymbolInfo &I, const T *D, const FullComment *C,
MangledStream << D->getNameAsString();
// A 250 length limit was chosen since 255 is a common limit across
// different filesystems, with a 5 character buffer for file extensions.
if (MangledName.size() > 250)
// File creation fails if the mangled name is too long, so default to the
// USR. We should look for a better check since filesystems differ in
// maximum filename length
I.MangledName = llvm::toStringRef(llvm::toHex(I.USR));
else
if (MangledName.size() > 250) {
auto SymbolID = llvm::toStringRef(llvm::toHex(I.USR)).str();
I.MangledName = MangledName.substr(0, 250 - SymbolID.size()) + SymbolID;
Comment on lines +784 to +785
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@ilovepi ilovepi Sep 22, 2025 •
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Its a micro optimization, but you can save 2 allocations by using Twine to concat in one go in the assignment. It does leave the code a bit less readable, but not too badly. Cant recall if the code below needs to be wrapped in ().str() or not either. But I'm also fine if you leave this as is.

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auto SymbolID = llvm::toStringRef(llvm::toHex(I.USR)).str();
I.MangledName = MangledName.substr(0, 250 - SymbolID.size()) + SymbolID;
I.MangledName = Twine(MangledName.substr(0, 250 - SymbolID.size())) + llvm::toStringRef(llvm::toHex(I.USR));

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I tried this but I need to know the hex version of the USR's length to subtract, not the Info's hashed SymbolID. I think the hex value is guaranteed to be at most 40. Do you know if that's an upper limit? There's a reference to that in the YAML generator. If it is a constant, this would work and be better than querying for the length since anything greater than that would break this anyways. The test has a 40 character hex.

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SymbolID is std::array<uint8_t,20>, so I'd guess thats why the length is fixed at 40, since you'd get 2chars per byte. the SHA1.cpp returns the same std::array<uint8_t,20> type, so I beleive you can rely on that as an upper limit, and sha1 has a 20 byte fixed size (160-bit).

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in any case, we can fix that later. its not important in the bigger scheme of things, and as i said is really just a micro optimization. we only do this once per file, so its not terrible, even for a large amount of files.

} else
I.MangledName = MangledName;
delete Mangler;
}
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4 changes: 2 additions & 2 deletions clang-tools-extra/test/clang-doc/long-name.cpp
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Expand Up @@ -9,6 +9,6 @@ struct ThisStructHasANameThatResultsInAMangledNameThatIsExactly250CharactersLong
struct ThisStructHasANameThatResultsInAMangledNameThatIsExactly251CharactersLongThatIsSupposedToTestTheFilenameLengthLimitsWithinClangDocInOrdertoSeeifclangdocwillcrashornotdependingonthelengthofthestructIfTheLengthIsTooLongThenClangDocWillCrashAnd123 {};

// CHECK-JSON: ThisStructHasANameThatResultsInAMangledNameThatIsExactly250CharactersLongThatIsSupposedToTestTheFilenameLengthLimitsWithinClangDocInOrdertoSeeifclangdocwillcrashornotdependingonthelengthofthestructIfTheLengthIsTooLongThenClangDocWillCrashAnd12.json
// CHECK-JSON: {{[0-9A-F]*}}.json
// CHECK-JSON: _ZTV244ThisStructHasANameThatResultsInAMangledNameThatIsExactly251CharactersLongThatIsSupposedToTestTheFilenameLengthLimitsWithinClangDocInOrdertoSeeifclangdocwillcrashornotdependingonthelengthofthestructIfTheL29DE8558215A13A506661C0E01E50AA3E5C9C7FA.json
// CHECK-HTML: ThisStructHasANameThatResultsInAMangledNameThatIsExactly250CharactersLongThatIsSupposedToTestTheFilenameLengthLimitsWithinClangDocInOrdertoSeeifclangdocwillcrashornotdependingonthelengthofthestructIfTheLengthIsTooLongThenClangDocWillCrashAnd12.html
// CHECK-HTML: {{[0-9A-F]*}}.html
// CHECK-HTML: _ZTV244ThisStructHasANameThatResultsInAMangledNameThatIsExactly251CharactersLongThatIsSupposedToTestTheFilenameLengthLimitsWithinClangDocInOrdertoSeeifclangdocwillcrashornotdependingonthelengthofthestructIfTheL29DE8558215A13A506661C0E01E50AA3E5C9C7FA.html