Try again to fix libcxx CMake so that it doesn't break when no LLVM source tree is available

[zturner]

Summary

This removes the configure step from libcxx CMake so it doesn't generate the output script.

I can probably get this added back later, but for now I'm just trying to get things green.

Note that libcxx CMake already depends on LLVM sources for running the test suite via a check target. It has been this way for some time and I didn't introduce this. These bots that broke, however, do not do that. They instead download lit and run it manually.

With this patch, that workflow should be supported again. Runing bin/llvm-lit -sv <libcxx-source-tree> isn't, but but the old workflow of using lit.py -sv <libcxx-source-tree> should still work.

If one of you at Apple + Eric could please try this I would appreciate.

[sqlbyme]

So after locally reverting r313643 and then applying only the patch related to libcxx/cmake/Modules/HandleOutOfTreeLLVM.cmake I was able to configure and build libcxx successfully.

[zturner]

Thanks, I will submit this in a couple of hours when I get into the office.

The llvm side changes are necessary to make ninja check-libcxx work (which these bots aren't using anyway)

[mgorny]

This actually breaks using external lit. It no longer respects -DLLVM_EXTERNAL_LIT passed to CMake, and instead forces the hardcoded libcxx path, which — since the file listed there doesn't exist — causes fallback to also-non-existing llvm-lit to happen.

libcxx/cmake/Modules/HandleOutOfTreeLLVM.cmake

if (NOT DEFINED LLVM_ENABLE_SPHINX)
     set(LLVM_ENABLE_SPHINX OFF)
   endif()
 
   # In a standalone build, we don't have llvm to automatically generate the
   # llvm-lit script for us.  So we need to provide an explicit directory that
   # the configurator should write the script into.
   set(LLVM_LIT_OUTPUT_DIR "${libcxx_BINARY_DIR}/bin")
 
+  if (LLVM_INCLUDE_TESTS)
     # Required LIT Configuration ------------------------------------------------
     # Define the default arguments to use with 'lit', and an option for the user
     # to override.
+    set(LLVM_EXTERNAL_LIT "${LLVM_MAIN_SRC_DIR}/utils/lit/lit.py")
     set(LIT_ARGS_DEFAULT "-sv --show-xfail --show-unsupported")
     if (MSVC OR XCODE)
       set(LIT_ARGS_DEFAULT "${LIT_ARGS_DEFAULT} --no-progress-bar")
     endif()
     set(LLVM_LIT_ARGS "${LIT_ARGS_DEFAULT}" CACHE STRING "Default options for lit")
+  endif()
 
   # Required doc configuration
   if (LLVM_ENABLE_SPHINX)
     find_package(Sphinx REQUIRED)
   endif()
 
   if (LLVM_ON_UNIX AND NOT APPLE)
     set(LLVM_HAVE_LINK_VERSION_SCRIPT 1)
   else()
     set(LLVM_HAVE_LINK_VERSION_SCRIPT 0)
   endif()
 endmacro(configure_out_of_tree_llvm)
 
 configure_out_of_tree_llvm()

llvm/cmake/modules/AddLLVM.cmake

foreach (_variableName ${_variableNames})
     message(STATUS "${_variableName}=${${_variableName}}")
   endforeach()
 endfunction()
 
 function(get_llvm_lit_path base_dir file_name)
   cmake_parse_arguments(ARG "ALLOW_EXTERNAL" "" "" ${ARGN})
 
   if (ARG_ALLOW_EXTERNAL)
+    set(LLVM_DEFAULT_EXTERNAL_LIT "${LLVM_EXTERNAL_LIT}")
     set (LLVM_EXTERNAL_LIT "" CACHE STRING "Command used to spawn lit")
+    if ("${LLVM_EXTERNAL_LIT}" STREQUAL "")
+      set(LLVM_EXTERNAL_LIT "${LLVM_DEFAULT_EXTERNAL_LIT}")
+    endif()
+
     if (NOT "${LLVM_EXTERNAL_LIT}" STREQUAL "")
       if (EXISTS ${LLVM_EXTERNAL_LIT})
         get_filename_component(LIT_FILE_NAME ${LLVM_EXTERNAL_LIT} NAME)
         get_filename_component(LIT_BASE_DIR ${LLVM_EXTERNAL_LIT} DIRECTORY)
         set(${file_name} ${LIT_FILE_NAME} PARENT_SCOPE)
         set(${base_dir} ${LIT_BASE_DIR} PARENT_SCOPE)
         return()
       else()
function(get_llvm_lit_path base_dir file_name)
   endif()
 
   # Allow individual projects to provide an override
   if (NOT "${LLVM_LIT_OUTPUT_DIR}" STREQUAL "")
     set(LLVM_LIT_BASE_DIR ${LLVM_LIT_OUTPUT_DIR})
   elseif(NOT "${LLVM_RUNTIME_OUTPUT_INTDIR}" STREQUAL "")
     set(LLVM_LIT_BASE_DIR ${LLVM_RUNTIME_OUTPUT_INTDIR})
   else()
-    message(WARNING "Could not find suitable output location for llvm-lit."
-                    "Using default ${CMAKE_CURRENT_BINARY_DIR}/llvm-lit")
-    set(LLVM_LIT_BASE_DIR ${CMAKE_CURRENT_BINARY_DIR}/llvm-lit)
+    set(LLVM_LIT_BASE_DIR "")
   endif()
 
   # Cache this so we don't have to do it again and have subsequent calls
   # potentially disagree on the value.
   set_property(GLOBAL PROPERTY LLVM_LIT_BASE_DIR ${LLVM_LIT_BASE_DIR})
   set(${base_dir} ${LLVM_LIT_BASE_DIR} PARENT_SCOPE)
 endfunction()