[PATCH] D12646: Add libc++ header path for DarwinClang builds

[don hinton via cfe-commits]

hintonda added a comment.

In http://reviews.llvm.org/D12646#241308, @kubabrecka wrote:

> In what scenario exactly are you seeing an issue?  If it's a just-built clang that can't find C++ headers, then you should just build the libcxx project alongside.


clang++ defaults to -stdlib=libc++ for newer versions of MacOS (see ToolChains.cpp:902), but since there isn't a way to pass corresponding include path via cmake, clang++ doesn't work out of the box, i.e., it only checks /usr/include/c++/v1, not the path relative to the version of clang used to build it.

I first noticed it when I tried to run the version of clang-tidy I'd just built and found I had to pass the path for it to find iostream.

> This is just a default location of Xcode.app and it's wrong to hardcode it, because the user can install Xcode to different locations (or have multiple installations). Even letting CMake find the path will be wrong, because the location of Xcode is a user's choice.


Yes, but if you allow the user to pass the include path via cmake, how could that be wrong?  This is equivalent to passing GCC_INSTALL_PREFIX so clang can find the gcc headers for libstdc++.

The user can always override it if they want to use a different version, but right now, overriding the location is the only way to make it work.  If we're not going to generate a working version using libc++, perhaps we shouldn't override -stdlib=libc++ unless the appropriate headers can't be found.


http://reviews.llvm.org/D12646