[lldb] Allow configuring on Windows with python interpreter within a junction

[zero9178]

Summary

The current implementation nicely takes into account when the python interpreter is symlinked (or transitively within a symlinked directory). Sadly, os.path.islink returns false on Windows if instead of Windows symlinks, junctions are used. This has caused me issues after I started using scoop as my package manager on Windows, which creates junctions instead of symlinks.
The fix proposed in this patch is to check whether realpath returns a different path to exe, and if it does, to simply try again with that path.
The code could also be simplified since sys.executable is guaranteed to be absolute, and os.readlink, which can return a relative path, is no longer used.

Tested on Windows 11 with Python 3.11 as interpereter and Ubuntu 18.04 with Python 3.6

[JDevlieghere]

Looks reasonable to me.

@lawrence_danna do you happen to remember why you wrote:

exe = os.path.join(os.path.realpath(os.path.dirname(exe)), os.readlink(exe))

instead of

exe = os.path.realpath(exe)

which seems like it should be equivalent? Aand you're doing a realpath call anyway...

[clayborg]

lgtm

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

elif args.variable_name == "LLDB_PYTHON_EXE_RELATIVE_PATH":
         exe = sys.executable
         prefix = os.path.realpath(sys.prefix)
         while True:
             try:
                 print(relpath_nodots(exe, prefix))
                 break
             except ValueError:
                 tried.append(exe)
-                if os.path.islink(exe):
-                    exe = os.path.join(os.path.realpath(os.path.dirname(exe)), os.readlink(exe))
+                # Retry if the executable is symlinked or similar.
+                # This is roughly equal to os.path.islink, except it also works for junctions on Windows.
+                if os.path.realpath(exe) != exe:
+                    exe = os.path.realpath(exe)
                     continue
                 else:
                     print("Could not find a relative path to sys.executable under sys.prefix", file=sys.stderr)
                     for e in tried:
                         print("tried:", e, file=sys.stderr)
                     print("realpath(sys.prefix):", prefix, file=sys.stderr)
                     print("sys.prefix:", sys.prefix, file=sys.stderr)
                     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()