Backport fixes from bpo-39769

https://bugs.python.org/issue39769
python/cpython#18676

Author: frenzymadness

compileall2.py

@@ -113,6 +113,13 @@ def compile_dir(dir, maxlevels=None, ddir=None, force=False,
     hardlink_dupes: hardlink duplicated pyc files
     """
     ProcessPoolExecutor = None
+    if ddir is not None and (stripdir is not None or prependdir is not None):
+        raise ValueError(("Destination dir (ddir) cannot be used "
+                          "in combination with stripdir or prependdir"))
+    if ddir is not None:
+        stripdir = dir
+        prependdir = ddir
+        ddir = None
     if workers is not None:
         if workers < 0:
             raise ValueError('workers must be greater or equal to 0')

test_compileall2.py

@@ -2,6 +2,7 @@
 import compileall2 as compileall
 import importlib.util
 import test.test_importlib.util
+import marshal
 import os
 import pathlib
 import py_compile
@@ -39,6 +40,19 @@ def _optim_args_from_interpreter_flags():
         args.append('-' + 'O' * value)
     return args
 
+# Backported from Lib/test/test_importlib/util.py
+# Added in: https://github.com/python/cpython/pull/18676/files
+def get_code_from_pyc(pyc_path):
+    """Reads a pyc file and returns the unmarshalled code object within.
+    No header validation is performed.
+    """
+    with open(pyc_path, 'rb') as pyc_f:
+        if compileall.PY37:
+            pyc_f.seek(16)
+        else:
+            pyc_f.seek(12)
+        return marshal.load(pyc_f)
+
 # Use the original one for Python > 3.5 and backported function otherwise
 if compileall.PY36:
     optim_args_from_interpreter_flags = support.optim_args_from_interpreter_flags
@@ -274,6 +288,47 @@ def test_compile_dir_maxlevels(self):
         compileall.compile_dir(self.directory, quiet=True, maxlevels=depth)
         self.assertTrue(os.path.isfile(pyc_filename))
 
+    def _test_ddir_only(self, *, ddir, parallel=True):
+        """Recursive compile_dir ddir must contain package paths; bpo39769."""
+        fullpath = ["test", "foo"]
+        path = self.directory
+        mods = []
+        for subdir in fullpath:
+            path = os.path.join(path, subdir)
+            os.mkdir(path)
+            script_helper.make_script(path, "__init__", "")
+            mods.append(script_helper.make_script(path, "mod",
+                                                  "def fn(): 1/0\nfn()\n"))
+        compileall.compile_dir(
+                self.directory, quiet=True, ddir=ddir,
+                workers=2 if parallel else 1)
+        self.assertTrue(mods)
+        for mod in mods:
+            self.assertTrue(mod.startswith(self.directory), mod)
+            modcode = importlib.util.cache_from_source(mod)
+            modpath = mod[len(self.directory+os.sep):]
+            _, _, err = script_helper.assert_python_failure(modcode)
+            expected_in = os.path.join(ddir, modpath)
+            mod_code_obj = get_code_from_pyc(modcode)
+            self.assertEqual(mod_code_obj.co_filename, expected_in)
+            self.assertIn('"{}"'.format(expected_in), os.fsdecode(err))
+
+    def test_ddir_only_one_worker(self):
+        """Recursive compile_dir ddir= contains package paths; bpo39769."""
+        return self._test_ddir_only(ddir="<a prefix>", parallel=False)
+
+    def test_ddir_multiple_workers(self):
+        """Recursive compile_dir ddir= contains package paths; bpo39769."""
+        return self._test_ddir_only(ddir="<a prefix>", parallel=True)
+
+    def test_ddir_empty_only_one_worker(self):
+        """Recursive compile_dir ddir='' contains package paths; bpo39769."""
+        return self._test_ddir_only(ddir="", parallel=False)
+
+    def test_ddir_empty_multiple_workers(self):
+        """Recursive compile_dir ddir='' contains package paths; bpo39769."""
+        return self._test_ddir_only(ddir="", parallel=True)
+
     def test_strip_only(self):
         fullpath = ["test", "build", "real", "path"]
         path = os.path.join(self.directory, *fullpath)