[libcxx-commits] [libcxx] [libcxx] [modules] Fix relative paths with absolute LIBCXX_INSTALL_MODULES_DIR (PR #85756)

[Martin Storsjö via libcxx-commits]

mstorsjo wrote:

> Hi, we're seeing the following error in our CI after this patch ... I'm not totally sure this is completely the right approach. We see this on all platforms(linux, windows, mac).
> 
> ```
> CMake Error at /b/s/w/ir/x/w/llvm-llvm-project/libcxx/modules/CMakeLists.txt:209 (cmake_path):
>   Error after keyword "BASE_DIRECTORY":
> 
>     missing required value
> 
> CMake Error at /b/s/w/ir/x/w/llvm-llvm-project/libcxx/modules/CMakeLists.txt:212 (cmake_path):
>   Error after keyword "BASE_DIRECTORY":
> 
>     missing required value
> 
> CMake Error at /b/s/w/ir/x/w/llvm-llvm-project/libcxx/modules/CMakeLists.txt:215 (file):
>   file RELATIVE_PATH called with incorrect number of arguments
> ```
> 
> https://ci.chromium.org/ui/p/fuchsia/builders/toolchain.ci/clang-linux-x64-rbe/b8752958259472772145/overview
> 
> Can you take a look and revert if it will be hard to fix quickly?

Hm, I guess this is possible if `CMAKE_INSTALL_PREFIX` is unset/empty. I'll push a potential fix for that, and if that doesn't help, let's revert.

https://github.com/llvm/llvm-project/pull/85756