ClangTidy: clang-analyzer-core.uninitialized.Branch in third_party/dawn/third_party/dxc/tools/clang/tools/libclang/CIndex.cpp

Description
A preprocessor defintion to block out code not needed for dxc means that TU is expected to be set via
clang_createTranslationUnit2's *out_TU = MakeCXTranslationUnit(CXXIdx, AU.release()); Even though it is not necessary for it to do so becauseCXTranslationUnit TU; is return by value via clang_createTranslationUnit.

https://github.com/microsoft/DirectXShaderCompiler/blob/ceff9b8043df3ac8d7d3ce71b409d83afcd7925b/tools/clang/tools/libclang/CIndex.cpp#L2944:2961

While this is a false positive it is the only case in chromium third party (https://chromium.googlesource.com/external/github.com/microsoft/DirectXShaderCompiler) that violates this rule.

An altenative:

CXTranslationUnit clang_createTranslationUnit(CXIndex CIdx,
                                              const char *ast_filename) {
  CXTranslationUnit TU;
#if 1 // HLSL Change Starts - no support for serialization
  enum CXErrorCode Result = CXError_Failure;
#else 
 enum CXErrorCode Result = 
      clang_createTranslationUnit2(CIdx, ast_filename, &TU);
#endif // HLSL Change Ends - no support for serialization
  (void)Result;
  assert((TU && Result == CXError_Success) ||
         (!TU && Result != CXError_Success));
  return TU;
}

This way you avoid calling clang_createTranslationUnit2 entirely.

Start in third_party/dawn/third_party/dxc/tools/clang/tools/libclang/CIndex.cpp around lines 2944-2961, focusing on clang_createTranslationUnit and clang_createTranslationUnit2. Review the preprocessor-controlled path and the proposed alternative, then verify that the clang-analyzer-core.uninitialized.Branch warning is resolved without changing the translation-unit behavior.