[LLDB] Don't use the local python to set a default for LLDB_PYTHON_RELATIVE_PATH when cross compiling.

[JDevlieghere]

lldb/CMakeLists.txt

54

Are there other reasons LLDB_PYTHON_RELATIVE_PATH could be empty at this point, unrelated to cross compilation? Would it make sense to move the error in the else clause of if (NOT CMAKE_CROSSCOMPILING) instead?

[mstorsjo]

lldb/CMakeLists.txt

54

I guess it could be if the python command above succeeded, but output an empty string.

My cmake-fu isn't very strong, but I wonder if it's ok to check ${LLDB_PYTHON_RELATIVE_PATH} before the set(LLDB_PYTHON_RELATIVE_PATH ${LLDB_PYTHON_DEFAULT_RELATIVE_PATH} CACHE ...) command? I guess it is, because it's going to need to be set beforehand anyway?

lldb/CMakeLists.txt

if(uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG" )
   add_definitions(-DLLDB_CONFIGURATION_DEBUG)
 endif()
 
 if (WIN32)
   add_definitions(-D_ENABLE_EXTENDED_ALIGNED_STORAGE)
 endif()
 
 if (LLDB_ENABLE_PYTHON)
+  if (NOT CMAKE_CROSSCOMPILING)
     execute_process(
       COMMAND ${Python3_EXECUTABLE}
           -c "import distutils.sysconfig; print(distutils.sysconfig.get_python_lib(True, False, ''))"
       OUTPUT_VARIABLE LLDB_PYTHON_DEFAULT_RELATIVE_PATH
       OUTPUT_STRIP_TRAILING_WHITESPACE)
 
     file(TO_CMAKE_PATH ${LLDB_PYTHON_DEFAULT_RELATIVE_PATH} LLDB_PYTHON_DEFAULT_RELATIVE_PATH)
+  else ()
+    if ("${LLDB_PYTHON_RELATIVE_PATH}" STREQUAL "")
+      message(FATAL_ERROR
+        "Crosscompiling LLDB with Python requires manually setting
+        LLDB_PYTHON_RELATIVE_PATH.")
+    endif ()
+  endif ()
+
   set(LLDB_PYTHON_RELATIVE_PATH ${LLDB_PYTHON_DEFAULT_RELATIVE_PATH}
     CACHE STRING "Path where Python modules are installed, relative to install prefix")
 endif ()
 
 if (LLDB_ENABLE_PYTHON OR LLDB_ENABLE_LUA)
   add_subdirectory(bindings)
 endif ()
 
 # We need the headers generated by instrinsics_gen before we can compile
 # any source file in LLDB as the imported Clang modules might include
 # some of these generated headers. This approach is copied from Clang's main
 # CMakeLists.txt, so it should kept in sync the code in Clang which was added
 # in llvm-svn 308844.