[PATCH] D89001: [clang] Don't look into <sysroot> for C++ headers if they are found alongside the toolchain

[Dmitry Polukhin via Phabricator via cfe-commits]

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@ldionne and @dexonsmith, it seems that this diff breaks clang-tools like clang-tidy and clangd if `-isysroot` is specified in the compilation database. Moreover, clang from Xcode 14 and 15 uses paths specified in `-sysroot` and ignores headers alongside the clang binary. I don’t know if it is new behavior or it was this way when this diff was committed. Minimal reproducer is following:

  $ cat compile_commands.json
  [
      {
          "directory": "/Users/test/test",
          "file": "test.cpp",
          "arguments": [
              "/Applications/Xcode_14.3.1_14E300b.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang++",
              "-isysroot",
              "/Applications/Xcode_14.3.1_14E300b.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk",
              "-c",
              "test.cpp",
              "-v"
          ]
      }
  ]
  
  $ <upstream>/build/bin/clang-tidy -p compile_commands.json test.cpp
  ...
  #include <...> search starts here:
   /Applications/Xcode_14.3.1_14E300b.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1
   <upstream>/build/lib/clang/18/include
   /Applications/Xcode_14.3.1_14E300b.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include
   /Applications/Xcode_14.3.1_14E300b.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks (framework directory)
  End of search list.
  1 error generated.
  Error while processing test.cpp.
  test.cpp:1:10: error: 'cxxabi.h' file not found [clang-diagnostic-error]
      1 | #include <cxxabi.h>
        |          ^~~~~~~~~~
  Found compiler error(s).
  
  $ /Applications/Xcode_14.3.1_14E300b.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang++ -isysroot /Applications/Xcode_14.3.1_14E300b.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk -c test.cpp -v
  ...
  #include <...> search starts here:
   /Applications/Xcode_14.3.1_14E300b.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1
   /Applications/Xcode_14.3.1_14E300b.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/14.0.3/include
   /Applications/Xcode_14.3.1_14E300b.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include
   /Applications/Xcode_14.3.1_14E300b.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include
   /Applications/Xcode_14.3.1_14E300b.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks (framework directory)
  End of search list.

So upstream clang-tools uses a path to the compiler binary specified in CDB as an installation dir and searches in ".../XcodeDefault.xctoolchain/usr/bin/../include/c++/v1" but the Apple compiler from CDB searches in the path specified in sysroot ".../MacOSX.sdk/usr/include/c++/v1". I also checked clangd from Apple toolchain, it also uses path species in `-sysroot`. I have a local patch that honors `-isysroot` if it is explicitly specified in the command line but prefers headers alongside the binary in other cases and it seems that it matches the behavior of Apple compiler.  But it breaks all tests that specifically test that `-isysroot` is ignored. Should I change the test and send the patch for review?


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D89001/new/

https://reviews.llvm.org/D89001