[Cmake] Unify python variables

[JDevlieghere]

Summary

Both FindPythonInterp and FindPythonLibs do two things, they'll set some variables (PYTHON_LIBRARIES, PYTHON_INCLUDE_DIRS) and update the cached variables (PYTHON_LIBRARY, PYTHON_INCLUDE_DIR) that are also used to specify a custom python installation.

I believe the canonical way to do this is to use the PYTHON_LIBRARIES and PYTHON_INCLUDE_DIRS variables instead of the cached ones. However, since the cached variables are accessible from the cache and GUI, this is a lot less confusing when you're trying to debug why a variable did or didn't get the value you expected. Furthermore, as far as I can tell, the implementation uses the cached variables to set their LIBRARIES/DIRS counterparts. This is also the reason this works today even though we mix-and-match.

[stella.stamenova]

LGTM

[labath]

lldb/cmake/modules/LLDBConfig.cmake

246–247

Is there any difference between include(FindPythonInterp) and find_package(PythonInterp)? It sounds like the latter should be used, because it's more specific, but I have no idea its possible to do that..

lldb/cmake/modules/LLDBConfig.cmake

     return()
   endif()
 
-  file(TO_CMAKE_PATH "${PYTHON_HOME}/Include" PYTHON_INCLUDE_DIRS)
+  file(TO_CMAKE_PATH "${PYTHON_HOME}/Include" PYTHON_INCLUDE_DIR)
 
-  if(EXISTS "${PYTHON_INCLUDE_DIRS}/patchlevel.h")
-    file(STRINGS "${PYTHON_INCLUDE_DIRS}/patchlevel.h" python_version_str
+  if(EXISTS "${PYTHON_INCLUDE_DIR}/patchlevel.h")
+    file(STRINGS "${PYTHON_INCLUDE_DIR}/patchlevel.h" python_version_str
          REGEX "^#define[ \t]+PY_VERSION[ \t]+\"[^\"]+\"")
     string(REGEX REPLACE "^#define[ \t]+PY_VERSION[ \t]+\"([^\"+]+)[+]?\".*" "\\1"
          PYTHONLIBS_VERSION_STRING "${python_version_str}")

     string(REGEX REPLACE "([0-9]+)[.]([0-9]+)[.][0-9]+" "python\\1\\2" PYTHONLIBS_BASE_NAME "${PYTHONLIBS_VERSION_STRING}")
     unset(python_version_str)
   else()
-    message("Unable to find ${PYTHON_INCLUDE_DIRS}/patchlevel.h, Python installation is corrupt.")
+    message("Unable to find ${PYTHON_INCLUDE_DIR}/patchlevel.h, Python installation is corrupt.")
     message("Python support will be disabled for this build.")
     set(LLDB_DISABLE_PYTHON 1 PARENT_SCOPE)
     return()

   set (PYTHON_EXECUTABLE ${PYTHON_EXECUTABLE} PARENT_SCOPE)
   set (PYTHON_LIBRARY ${PYTHON_LIBRARY} PARENT_SCOPE)
   set (PYTHON_DLL ${PYTHON_DLL} PARENT_SCOPE)
-  set (PYTHON_INCLUDE_DIRS ${PYTHON_INCLUDE_DIRS} PARENT_SCOPE)
+  set (PYTHON_INCLUDE_DIR ${PYTHON_INCLUDE_DIR} PARENT_SCOPE)
 
   message("-- LLDB Found PythonExecutable: ${PYTHON_RELEASE_EXE} and ${PYTHON_DEBUG_EXE}")
   message("-- LLDB Found PythonLibs: ${PYTHON_RELEASE_LIB} and ${PYTHON_DEBUG_LIB}")
   message("-- LLDB Found PythonDLL: ${PYTHON_RELEASE_DLL} and ${PYTHON_DEBUG_DLL}")
-  message("-- LLDB Found PythonIncludeDirs: ${PYTHON_INCLUDE_DIRS}")
+  message("-- LLDB Found PythonIncludeDirs: ${PYTHON_INCLUDE_DIR}")
 endfunction(find_python_libs_windows)
 
 if (NOT LLDB_DISABLE_PYTHON)

       add_definitions( -DLLDB_PYTHON_HOME="${LLDB_PYTHON_HOME}" )
     endif()
   else()
-    find_package(PythonLibs REQUIRED)
+    include(FindPythonInterp)
+    include(FindPythonLibs)
   endif()
-  
-  if (PYTHON_INCLUDE_DIRS)
-    include_directories(${PYTHON_INCLUDE_DIRS})
+  if (PYTHON_INCLUDE_DIR)
+    include_directories(${PYTHON_INCLUDE_DIR})
   endif()
 endif()
 
 if (LLDB_DISABLE_PYTHON)
-  unset(PYTHON_INCLUDE_DIRS)
+  unset(PYTHON_INCLUDE_DIR)
   unset(PYTHON_LIBRARY)
+  unset(PYTHON_EXECUTABLE)
   add_definitions( -DLLDB_DISABLE_PYTHON )
 endif()
 

lldb/scripts/CMakeLists.txt

   ${LLDB_SOURCE_DIR}/include/lldb/lldb-versioning.h
 )
 
-include(FindPythonInterp)
-
 if(LLDB_BUILD_FRAMEWORK)
   set(framework_arg --framework --target-platform Darwin)
 endif()

lldb/scripts/Python/modules/readline/CMakeLists.txt

 # FIXME: if a non-standard version of python is requested, the cmake macro
 # below will need Python_ADDITIONAL_VERSIONS set in order to find it.
-include(FindPythonInterp)
 SET(PYTHON_DIRECTORY python${PYTHON_VERSION_MAJOR}.${PYTHON_VERSION_MINOR}/site-packages)
 
 # Build the readline python module

lldb/source/Utility/CMakeLists.txt

 endif()
 
 if (NOT LLDB_DISABLE_PYTHON AND NOT LLVM_BUILD_STATIC)
-  list(APPEND LLDB_SYSTEM_LIBS ${PYTHON_LIBRARIES})
+  list(APPEND LLDB_SYSTEM_LIBS ${PYTHON_LIBRARY})
 endif()
 
 list(APPEND LLDB_SYSTEM_LIBS ${system_libs})