Issue #13930: Adds ability for 2to3 to write its output to a different

directory tree instead of overwriting the input files.  Adds three command
line options: -o/--output-dir, -W/--write-unchanged-files and --add-suffix.

Feature backports into stable release branches for 2to3 are allowed by
a special exemption:
 http://mail.python.org/pipermail/python-dev/2011-December/115089.html

Lib/lib2to3/tests/test_main.py

@@ -1,18 +1,30 @@
 # -*- coding: utf-8 -*-
-import sys
 import codecs
-import logging
 import io
+import logging
+import os
+import shutil
+import sys
+import tempfile
 import unittest
 
 from lib2to3 import main
 
 
+TEST_DATA_DIR = os.path.join(os.path.dirname(__file__), "data")
+PY2_TEST_MODULE = os.path.join(TEST_DATA_DIR, "py2_test_grammar.py")
+
+
 class TestMain(unittest.TestCase):
 
+    def setUp(self):
+        self.temp_dir = None  # tearDown() will rmtree this directory if set.
+
     def tearDown(self):
         # Clean up logging configuration down by main.
         del logging.root.handlers[:]
+        if self.temp_dir:
+            shutil.rmtree(self.temp_dir)
 
     def run_2to3_capture(self, args, in_capture, out_capture, err_capture):
         save_stdin = sys.stdin
@@ -39,3 +51,85 @@ class TestMain(unittest.TestCase):
         self.assertTrue("-print 'nothing'" in output)
         self.assertTrue("WARNING: couldn't encode <stdin>'s diff for "
                         "your terminal" in err.getvalue())
+
+    def setup_test_source_trees(self):
+        """Setup a test source tree and output destination tree."""
+        self.temp_dir = tempfile.mkdtemp()  # tearDown() cleans this up.
+        self.py2_src_dir = os.path.join(self.temp_dir, "python2_project")
+        self.py3_dest_dir = os.path.join(self.temp_dir, "python3_project")
+        os.mkdir(self.py2_src_dir)
+        os.mkdir(self.py3_dest_dir)
+        # Turn it into a package with a few files.
+        self.setup_files = []
+        open(os.path.join(self.py2_src_dir, "__init__.py"), "w").close()
+        self.setup_files.append("__init__.py")
+        shutil.copy(PY2_TEST_MODULE, self.py2_src_dir)
+        self.setup_files.append(os.path.basename(PY2_TEST_MODULE))
+        self.trivial_py2_file = os.path.join(self.py2_src_dir, "trivial.py")
+        self.init_py2_file = os.path.join(self.py2_src_dir, "__init__.py")
+        with open(self.trivial_py2_file, "w") as trivial:
+            trivial.write("print 'I need a simple conversion.'")
+        self.setup_files.append("trivial.py")
+
+    def test_filename_changing_on_output_single_dir(self):
+        """2to3 a single directory with a new output dir and suffix."""
+        self.setup_test_source_trees()
+        out = io.StringIO()
+        err = io.StringIO()
+        suffix = "TEST"
+        ret = self.run_2to3_capture(
+                ["-n", "--add-suffix", suffix, "--write-unchanged-files",
+                 "--no-diffs", "--output-dir",
+                 self.py3_dest_dir, self.py2_src_dir],
+                io.StringIO(""), out, err)
+        self.assertEqual(ret, 0)
+        stderr = err.getvalue()
+        self.assertIn(" implies -w.", stderr)
+        self.assertIn(
+                "Output in %r will mirror the input directory %r layout" % (
+                        self.py3_dest_dir, self.py2_src_dir), stderr)
+        self.assertEqual(set(name+suffix for name in self.setup_files),
+                         set(os.listdir(self.py3_dest_dir)))
+        for name in self.setup_files:
+            self.assertIn("Writing converted %s to %s" % (
+                    os.path.join(self.py2_src_dir, name),
+                    os.path.join(self.py3_dest_dir, name+suffix)), stderr)
+        self.assertRegexpMatches(stderr, r"No changes to .*/__init__\.py")
+        self.assertNotRegex(stderr, r"No changes to .*/trivial\.py")
+
+    def test_filename_changing_on_output_two_files(self):
+        """2to3 two files in one directory with a new output dir."""
+        self.setup_test_source_trees()
+        err = io.StringIO()
+        py2_files = [self.trivial_py2_file, self.init_py2_file]
+        expected_files = set(os.path.basename(name) for name in py2_files)
+        ret = self.run_2to3_capture(
+                ["-n", "-w", "--write-unchanged-files",
+                 "--no-diffs", "--output-dir", self.py3_dest_dir] + py2_files,
+                io.StringIO(""), io.StringIO(), err)
+        self.assertEqual(ret, 0)
+        stderr = err.getvalue()
+        self.assertIn(
+                "Output in %r will mirror the input directory %r layout" % (
+                        self.py3_dest_dir, self.py2_src_dir), stderr)
+        self.assertEqual(expected_files, set(os.listdir(self.py3_dest_dir)))
+
+    def test_filename_changing_on_output_single_file(self):
+        """2to3 a single file with a new output dir."""
+        self.setup_test_source_trees()
+        err = io.StringIO()
+        ret = self.run_2to3_capture(
+                ["-n", "-w", "--no-diffs", "--output-dir", self.py3_dest_dir,
+                 self.trivial_py2_file],
+                io.StringIO(""), io.StringIO(), err)
+        self.assertEqual(ret, 0)
+        stderr = err.getvalue()
+        self.assertIn(
+                "Output in %r will mirror the input directory %r layout" % (
+                        self.py3_dest_dir, self.py2_src_dir), stderr)
+        self.assertEqual(set([os.path.basename(self.trivial_py2_file)]),
+                         set(os.listdir(self.py3_dest_dir)))
+
+
+if __name__ == '__main__':
+    unittest.main()