clang/cmake: Drop use of llvm-config for LLVM install discovery

[Ericson2314]

Summary

This has been deprecated for a while, since D51714 in 2018.

Remove it in favor of using CMake's find_package() function.

[tstellar]

Rebase.

[tstellar]

clang/CMakeLists.txt

21–23

This doesn't look right (even though it passes my testing). I need to update this part of the patch.

[tstellar]

Remove more of the existing code.

[tstellar]

clang/CMakeLists.txt

21–23

I fixed this by removing of of the existing code that copied values from LLVMConfig.cmake.

[phosek]

This is similar to @Ericson2314's change D130735 which also removes llvm-config from LLD. I'm fine with either of the two changes. It might be better to land the Clang and LLD changes separately so they can be reverted separately if needed.

[tstellar]

@Ericson2314 Your version of these patches removed a few more things than mine (which seems better to me), do you want to just split your patch and commit the parts separately?

[Ericson2314]

Add my changes but split to just Clang as @tstellar requested

[mgorny]

This one LGTM to me as well, and doesn't seem to break Gentoo either ;-).

clang/CMakeLists.txt

 # Must go below project(..)
 include(GNUInstallDirs)
 
 if(CLANG_BUILT_STANDALONE)
   set(CMAKE_CXX_STANDARD 14 CACHE STRING "C++ standard to conform to")
   set(CMAKE_CXX_STANDARD_REQUIRED YES)
   set(CMAKE_CXX_EXTENSIONS NO)
 
-  # Rely on llvm-config.
-  set(LLVM_CONFIG_OUTPUT)
-  if(LLVM_CONFIG)
-    set (LLVM_CONFIG_FOUND 1)
-    message(STATUS "Found LLVM_CONFIG as ${LLVM_CONFIG}")
-    message(DEPRECATION "Using llvm-config to detect the LLVM installation is \
-          deprecated.  The installed cmake files should be used \
-          instead.  CMake should be able to detect your LLVM install \
-          automatically, but you can also use LLVM_DIR to specify \
-          the path containing LLVMConfig.cmake.")
-    set(CONFIG_COMMAND ${LLVM_CONFIG}
-      "--includedir"
-      "--prefix"
-      "--src-root"
-      "--cmakedir"
-      "--bindir"
-      "--libdir"
-      "--assertion-mode"
-      )
-    execute_process(
-      COMMAND ${CONFIG_COMMAND}
-      RESULT_VARIABLE HAD_ERROR
-      OUTPUT_VARIABLE LLVM_CONFIG_OUTPUT
-    )
-    if(NOT HAD_ERROR)
-      string(REGEX REPLACE
-        "[ \t]*[\r\n]+[ \t]*" ";"
-        LLVM_CONFIG_OUTPUT ${LLVM_CONFIG_OUTPUT})
-    else()
-      string(REPLACE ";" " " CONFIG_COMMAND_STR "${CONFIG_COMMAND}")
-      message(STATUS "${CONFIG_COMMAND_STR}")
-      message(FATAL_ERROR "llvm-config failed with status ${HAD_ERROR}")
-    endif()
-
-    list(GET LLVM_CONFIG_OUTPUT 0 MAIN_INCLUDE_DIR)
-    list(GET LLVM_CONFIG_OUTPUT 1 LLVM_OBJ_ROOT)
-    list(GET LLVM_CONFIG_OUTPUT 2 MAIN_SRC_DIR)
-    list(GET LLVM_CONFIG_OUTPUT 3 LLVM_CONFIG_CMAKE_DIR)
-    list(GET LLVM_CONFIG_OUTPUT 4 TOOLS_BINARY_DIR)
-    list(GET LLVM_CONFIG_OUTPUT 5 LIBRARY_DIR)
-    list(GET LLVM_CONFIG_OUTPUT 6 ENABLE_ASSERTIONS)
-
-    # Normalize LLVM_CMAKE_DIR. --cmakedir might contain backslashes.
-    # CMake assumes slashes as PATH.
-    file(TO_CMAKE_PATH ${LLVM_CONFIG_CMAKE_DIR} LLVM_CMAKE_DIR)
-  endif()
-
-
-  if(NOT MSVC_IDE)
-    set(LLVM_ENABLE_ASSERTIONS ${ENABLE_ASSERTIONS}
-      CACHE BOOL "Enable assertions")
-    # Assertions should follow llvm-config's.
-    mark_as_advanced(LLVM_ENABLE_ASSERTIONS)
-  endif()
-
   find_package(LLVM REQUIRED HINTS "${LLVM_CMAKE_DIR}")
   list(APPEND CMAKE_MODULE_PATH "${LLVM_DIR}")
 
-  # We can't check LLVM_CONFIG here, because find_package(LLVM ...) also sets
-  # LLVM_CONFIG.
-  if (NOT LLVM_CONFIG_FOUND)
-    # Pull values from LLVMConfig.cmake.  We can drop this once the llvm-config
-    # path is removed.
-    set(INCLUDE_DIRS ${LLVM_INCLUDE_DIRS})
-    set(LLVM_OBJ_DIR "${LLVM_BINARY_DIR}")
-    # N.B. this is just a default value, the CACHE PATHs below can be overriden.
-    set(MAIN_SRC_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../llvm")
-    set(TOOLS_BINARY_DIR "${LLVM_TOOLS_BINARY_DIR}")
-    set(LIBRARY_DIR "${LLVM_LIBRARY_DIR}")
-  else()
-    set(INCLUDE_DIRS "${LLVM_BINARY_DIR}/include" "${MAIN_INCLUDE_DIR}")
-  endif()
+  set(INCLUDE_DIRS "${LLVM_BINARY_DIR}/include" "${MAIN_INCLUDE_DIR}")
+  # Pull values from LLVMConfig.cmake.
+  set(MAIN_INCLUDE_DIR "${LLVM_INCLUDE_DIR}")
 
   set(LLVM_INCLUDE_DIRS ${INCLUDE_DIRS} CACHE PATH "Path to llvm/include and any other header dirs needed")
   set(LLVM_BINARY_DIR "${LLVM_OBJ_ROOT}" CACHE PATH "Path to LLVM build tree")
   set(LLVM_MAIN_SRC_DIR "${MAIN_SRC_DIR}" CACHE PATH "Path to LLVM source tree")
   set(LLVM_TOOLS_BINARY_DIR "${TOOLS_BINARY_DIR}" CACHE PATH "Path to llvm/bin")
   set(LLVM_LIBRARY_DIR "${LIBRARY_DIR}" CACHE PATH "Path to llvm/lib")
 
   find_program(LLVM_TABLEGEN_EXE "llvm-tblgen" ${LLVM_TOOLS_BINARY_DIR}