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

[Louis Dionne via Phabricator via cfe-commits]

ldionne created this revision.
ldionne added reviewers: arphaman, dexonsmith.
Herald added subscribers: cfe-commits, jkorous.
Herald added a project: clang.
ldionne requested review of this revision.

Currently, Clang looks for libc++ headers alongside the installation
directory of Clang, and it also adds a search path for headers in the
-isysroot. This is problematic if headers are found in both the toolchain
and in the sysroot, since #include_next will end up finding the libc++
headers in the sysroot instead of the intended system headers.

This patch changes the logic such that if the toolchain contains libc++
headers, no C++ header paths are added in the sysroot. However, if the
toolchain does *not* contain libc++ headers, the sysroot is searched as
usual.

This should not be a breaking change, since any code that previously
relied on some libc++ headers being found in the sysroot suffered from
the #include_next issue described above, which renders any libc++ header
basically useless.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D89001

Files:
  clang/lib/Driver/ToolChains/Darwin.cpp
  clang/test/Driver/Inputs/basic_darwin_sdk_usr_cxx_v1/usr/include/c++/v1/.keep
  clang/test/Driver/Inputs/basic_darwin_sdk_usr_cxx_v1/usr/lib/.keep
  clang/test/Driver/darwin-header-search-libcxx.cpp

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