[lldb] remove usage of distutils, fix python path on debian/ubuntu

[lawrence_danna]

Summary

distutils is deprecated and will be removed, so we shouldn't be
using it.

We were using it to compute LLDB_PYTHON_RELATIVE_PATH.

Discussing a similar issue
at python.org, Filipe Laíns said:

If you are relying on the value of distutils.sysconfig.get_python_lib()
as you shown in your system, you probably don't want to. That
directory (dist-packages) should be for Debian provided packages
only, so moving to sysconfig.get_path() would be a good thing,
as it has the correct value for user installed packages on your
system.

So I propose using a relative path from sys.prefix to
sysconfig.get_path("platlib") instead.

On Mac and windows, this results in the same paths as we had before,
which are lib/python3.9/site-packages and Lib\site-packages,
respectively.

On ubuntu however, this will change the path from
lib/python3/dist-packages to lib/python3.9/site-packages.

This change seems to be correct, as Filipe said above, dist-packages
belongs to the distribution, not us.

[labath]

I guess the correct path might depend on the precise value of "us". The ubuntu packagers might still want to put the files at that location, but they can just use the cmake variable to do that.

lldb/CMakeLists.txt

 endif()
 
 if (WIN32)
   add_definitions(-D_ENABLE_EXTENDED_ALIGNED_STORAGE)
 endif()
 
 if (LLDB_ENABLE_PYTHON)
   set(cachestring_LLDB_PYTHON_RELATIVE_PATH
-    "Path where Python modules are installed, relative to install prefix")
+    "Path where Python modules are installed, relative to LLDB's install prefix")
   set(cachestring_LLDB_PYTHON_EXE_RELATIVE_PATH
-    "Path to python interpreter exectuable, relative to install prefix")
+    "Path to python interpreter exectuable, relative to python's install prefix")
   set(cachestring_LLDB_PYTHON_EXT_SUFFIX
     "Filename extension for native code python modules")
 
   foreach(var LLDB_PYTHON_RELATIVE_PATH LLDB_PYTHON_EXE_RELATIVE_PATH LLDB_PYTHON_EXT_SUFFIX)
     if(NOT DEFINED ${var} AND NOT CMAKE_CROSSCOMPILING)
       execute_process(
         COMMAND ${Python3_EXECUTABLE}
           ${CMAKE_CURRENT_SOURCE_DIR}/bindings/python/get-python-config.py

lldb/bindings/python/get-python-config.py

 #!/usr/bin/env python3
 
 import os
 import sys
 import argparse
 import sysconfig
-import distutils.sysconfig
 
 
 def relpath_nodots(path, base):
     rel = os.path.normpath(os.path.relpath(path, base))
     assert not os.path.isabs(rel)
     parts = rel.split(os.path.sep)
     if parts and parts[0] == '..':
         raise ValueError(f"{path} is not under {base}")
     return rel
 
 def main():
     parser = argparse.ArgumentParser(description="extract cmake variables from python")
     parser.add_argument("variable_name")
     args = parser.parse_args()
     if args.variable_name == "LLDB_PYTHON_RELATIVE_PATH":
-        print(distutils.sysconfig.get_python_lib(True, False, ''))
+        # LLDB_PYTHON_RELATIVE_PATH is the relative path from lldb's prefix
+        # to where lldb's python libraries will be installed.
+        #
+        # The way we're going to compute this is to take the relative path from
+        # PYTHON'S prefix to where python libraries are supposed to be
+        # installed.
+        #
+        # The result is if LLDB and python are give the same prefix, then
+        # lldb's python lib will be put in the correct place for python to find it.
+        # If not, you'll have to use lldb -P or lldb -print-script-interpreter-info
+        # to figure out where it is.
+        print(relpath_nodots(sysconfig.get_path("platlib"), sys.prefix))
     elif args.variable_name == "LLDB_PYTHON_EXE_RELATIVE_PATH":
         tried = list()
         exe = sys.executable
         prefix = os.path.realpath(sys.prefix)
         while True:
             try:
                 print(relpath_nodots(exe, prefix))
                 break
elif args.variable_name == "LLDB_PYTHON_EXE_RELATIVE_PATH":
                     sys.exit(1)
     elif args.variable_name == "LLDB_PYTHON_EXT_SUFFIX":
         print(sysconfig.get_config_var('EXT_SUFFIX'))
     else:
         parser.error(f"unknown variable {args.variable_name}")
 
 if __name__ == '__main__':
     main()
 No newline at end of file