Findzstd.cmake: string sub-command REGEX, mode REPLACE: regex "$" matched an empty string.

[Vassil Vassilev]

When using find_package(llvm) on windows we get:

CMake Error at D:/bld/cppinterop_1709495262007/_h_env/Library/lib/cmake/llvm/Findzstd.cmake:39 (string):
2024-03-03T19:54:48.3232894Z   string sub-command REGEX, mode REPLACE: regex "$" matched an empty string.
2024-03-03T19:54:48.3233394Z Call Stack (most recent call first):
2024-03-03T19:54:48.3233750Z   D:/bld/cppinterop_1709495262007/_h_env/Library/lib/cmake/llvm/LLVMConfig.cmake:278 (find_package)
2024-03-03T19:54:48.3234068Z   CMakeLists.txt:121 (find_package)

Our diagnosis is that find_package(LLVM REQUIRED CONFIG) triggers LLVMConfig.cmake to call find_package(zstd). In the MSVC branch we use string(REGEX REPLACE "${CMAKE_INSTALL_LIBDIR}$" "${CMAKE_INSTALL_BINDIR}" zstd_DIRNAME "${zstd_DIRNAME}"), however, CMAKE_INSTALL_LIBDIR is not defined yet and we error out:

llvm-project/llvm/cmake/modules/Findzstd.cmake

Lines 36 to 47 in da5966e

 if(MSVC) 
   # IMPORTED_LOCATION is the path to the DLL and IMPORTED_IMPLIB is the "library". 
   get_filename_component(zstd_DIRNAME "${zstd_LIBRARY}" DIRECTORY) 
   string(REGEX REPLACE "${CMAKE_INSTALL_LIBDIR}$" "${CMAKE_INSTALL_BINDIR}" zstd_DIRNAME "${zstd_DIRNAME}") 
   get_filename_component(zstd_BASENAME "${zstd_LIBRARY}" NAME) 
   string(REGEX REPLACE "\\${CMAKE_LINK_LIBRARY_SUFFIX}$" "${CMAKE_SHARED_LIBRARY_SUFFIX}" zstd_BASENAME "${zstd_BASENAME}") 
   set_target_properties(zstd::libzstd_shared PROPERTIES 
       INTERFACE_INCLUDE_DIRECTORIES "${zstd_INCLUDE_DIR}" 
       IMPORTED_LOCATION "${zstd_DIRNAME}/${zstd_BASENAME}" 
       IMPORTED_IMPLIB "${zstd_LIBRARY}") 
   unset(zstd_DIRNAME) 
   unset(zstd_BASENAME) 

Adding include(GNUInstallDirs) which defines CMAKE_INSTALL_LIBDIR in the calling cmake fixes the problem but it's difficult to debug and and far from optimal.

Full log is here: https://dev.azure.com/conda-forge/84710dde-1620-425b-80d0-4cf5baca359d/_apis/build/builds/888296/logs/24