[PATCH] D136315: [clang][Darwin] Try to guess the SDK root with xcrun when unspecified

[Steven Wu via Phabricator via cfe-commits]

steven_wu added a comment.

In D136315#4069582 <https://reviews.llvm.org/D136315#4069582>, @calebzulawski wrote:

> That makes more sense, I thought perhaps it was using `DEFAULT_SYSROOT`.  The shim isn't smart enough to choose the sysroot from the target unfortunately.
>
> It looks like the only error is unrelated to this change, something with concepts in libc++.

The shim only works if you invoke `/usr/bin/clang`, and that shim is for building host OS. I am not sure it is a desirable behavior for clang to call into `xcrun` because it can be very slow on first invocation and you will get error if you don't have Xcode or Commandlinetools installed (on a basic macOS install basically).

I wonder if the better solution is print a very actionable diagnostics when building c++ but standard c++ library cannot be found.


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https://reviews.llvm.org/D136315