gh-105931: Fix surprising compileall stripdir behaviour (GH-108671)

Before, the '-s STRIPDIR' option on compileall lead to some surprising results as it only strips away path components that match, but leaves alone the non-matching ones interspersed in between. For example, with: python -m compileall -s/path/to/another/src /path/to/build/src/file.py The resulting written path will be: build/file.py This fix only strips directories that are a fully matching prefix of the source path. If a stripdir is provided that is not a valid prefix, a warning will be displayed (which can be silenced with '-qq').

Author: hetmankp

Lib/compileall.py

@@ -172,13 +172,13 @@ def compile_file(fullname, ddir=None, force=False, rx=None, quiet=0,
  if stripdir is not None:
  fullname_parts = fullname.split(os.path.sep)
  stripdir_parts = stripdir.split(os.path.sep)
- ddir_parts = list(fullname_parts)
 
- for spart, opart in zip(stripdir_parts, fullname_parts):
- if spart == opart:
- ddir_parts.remove(spart)
-
- dfile = os.path.join(*ddir_parts)
+ if stripdir_parts != fullname_parts[:len(stripdir_parts)]:
+ if quiet < 2:
+ print("The stripdir path {!r} is not a valid prefix for "
+ "source path {!r}; ignoring".format(stripdir, fullname))
+ else:
+ dfile = os.path.join(*fullname_parts[len(stripdir_parts):])
 
  if prependdir is not None:
  if dfile is None:

Lib/test/test_compileall.py

@@ -362,6 +362,29 @@ def test_strip_only(self):
  str(err, encoding=sys.getdefaultencoding())
  )
 
+ def test_strip_only_invalid(self):
+ fullpath = ["test", "build", "real", "path"]
+ path = os.path.join(self.directory, *fullpath)
+ os.makedirs(path)
+ script = script_helper.make_script(path, "test", "1 / 0")
+ bc = importlib.util.cache_from_source(script)
+ stripdir = os.path.join(self.directory, *(fullpath[:2] + ['fake']))
+ compileall.compile_dir(path, quiet=True, stripdir=stripdir)
+ rc, out, err = script_helper.assert_python_failure(bc)
+ expected_not_in = os.path.join(self.directory, *fullpath[2:])
+ self.assertIn(
+ path,
+ str(err, encoding=sys.getdefaultencoding())
+ )
+ self.assertNotIn(
+ expected_not_in,
+ str(err, encoding=sys.getdefaultencoding())
+ )
+ self.assertNotIn(
+ stripdir,
+ str(err, encoding=sys.getdefaultencoding())
+ )
+
  def test_prepend_only(self):
  fullpath = ["test", "build", "real", "path"]
  path = os.path.join(self.directory, *fullpath)

Misc/NEWS.d/next/Library/2023-08-30-19-10-35.gh-issue-105931.Lpwve8.rst

@@ -0,0 +1,8 @@
+Change :mod:`compileall` to only strip the stripdir prefix from the full path
+recorded in the compiled ``.pyc`` file, when the prefix matches the start of
+the full path in its entirety. When the prefix does not match, no stripping is
+performed and a warning to this effect is displayed.
+
+Previously all path components of the stripdir prefix that matched the full
+path were removed, while those that did not match were left alone (including
+ones interspersed between matching components).