support extend-exclude Fixes #535

6 files changed, 70 insertions, 9 deletions

diff --git a/docs/source/user/options.rst b/docs/source/user/options.rst
index 3b1c43d..ce0cf18 100644
--- a/docs/source/user/options.rst
+++ b/docs/source/user/options.rst
@@ -257,6 +257,38 @@ Options and their Descriptions
             __pycache__
 
 
+.. option:: --extend-exclude=<patterns>
+
+    :ref:`Go back to index <top>`
+
+    .. versionadded:: 3.8.0
+
+    Provide a comma-separated list of glob patterns to add to the list of excluded ones.
+    Similar considerations as in :option:`--exclude` apply here with regard to the
+    value.
+
+    The difference to the :option:`--exclude` option is, that this option can be
+    used to selectively add individual patterns without overriding the default
+    list entirely.
+
+    Command-line example:
+
+    .. prompt:: bash
+
+        flake8 --extend-exclude=legacy/,vendor/ dir/
+
+    This **can** be specified in config files.
+
+    Example config file usage:
+
+    .. code-block:: ini
+
+        extend-exclude =
+            legacy/,
+            vendor/
+        extend-exclude = legacy/,vendor/
+
+
 .. option:: --filename=<patterns>
 
     :ref:`Go back to index <top>`
diff --git a/src/flake8/checker.py b/src/flake8/checker.py
index 52a6a70..405820c 100644
--- a/src/flake8/checker.py
+++ b/src/flake8/checker.py
@@ -1,6 +1,7 @@
 """Checker Manager and Checker classes."""
 import collections
 import errno
+import itertools
 import logging
 import signal
 import tokenize
@@ -79,6 +80,9 @@ class Manager(object):
             "physical lines": 0,
             "tokens": 0,
         }
+        self.exclude = tuple(
+            itertools.chain(self.options.exclude, self.options.extend_exclude),
+        )
 
     def _process_statistics(self):
         for checker in self.checkers:
@@ -187,7 +191,7 @@ class Manager(object):
 
         return utils.matches_filename(
             path,
-            patterns=self.options.exclude,
+            patterns=self.exclude,
             log_message='"%(path)s" has %(whether)sbeen excluded',
             logger=LOG,
         )
diff --git a/src/flake8/main/options.py b/src/flake8/main/options.py
index d2a7159..e1f1767 100644
--- a/src/flake8/main/options.py
+++ b/src/flake8/main/options.py
@@ -14,6 +14,7 @@ def register_default_options(option_manager):
     - ``--count``
     - ``--diff``
     - ``--exclude``
+    - ``--extend-exclude``
     - ``--filename``
     - ``--format``
     - ``--hang-closing``
@@ -86,6 +87,16 @@ def register_default_options(option_manager):
     )
 
     add_option(
+        "--extend-exclude",
+        metavar="patterns",
+        default="",
+        parse_from_config=True,
+        comma_separated_list=True,
+        help="Comma-separated list of files or directories to add to the list"
+        " of excluded ones."
+    )
+
+    add_option(
         "--filename",
         metavar="patterns",
         default="*.py",
diff --git a/tests/integration/test_checker.py b/tests/integration/test_checker.py
index a17e5cd..ca3ed4f 100644
--- a/tests/integration/test_checker.py
+++ b/tests/integration/test_checker.py
@@ -206,8 +206,7 @@ def test_report_order(results, expected_order):
     file_checker.results = results
     file_checker.display_name = 'placeholder'
 
-    style_guide = mock.Mock(spec=['options'])
-    style_guide.processing_file = mock.MagicMock()
+    style_guide = mock.MagicMock(spec=['options', 'processing_file'])
 
     # Create a placeholder manager without arguments or plugins
     # Just add one custom file checker which just provides the results
diff --git a/tests/integration/test_main.py b/tests/integration/test_main.py
index 43cc168..21fd9e0 100644
--- a/tests/integration/test_main.py
+++ b/tests/integration/test_main.py
@@ -60,6 +60,22 @@ t.py:2:1: F401 'sys' imported but unused
     assert err == ''
 
 
+def test_extend_exclude(tmpdir, capsys):
+    """Ensure that `flake8 --extend-exclude` works."""
+    for d in ['project', 'vendor', 'legacy', '.git', '.tox', '.hg']:
+        tmpdir.mkdir(d).join('t.py').write('import os\nimport sys\n')
+
+    with tmpdir.as_cwd():
+        application.Application().run(['--extend-exclude=vendor,legacy'])
+
+    out, err = capsys.readouterr()
+    assert out == '''\
+./project/t.py:1:1: F401 'os' imported but unused
+./project/t.py:2:1: F401 'sys' imported but unused
+'''
+    assert err == ''
+
+
 def test_malformed_per_file_ignores_error(tmpdir, capsys):
     """Test the error message for malformed `per-file-ignores`."""
     setup_cfg = '''\
diff --git a/tests/unit/test_checker_manager.py b/tests/unit/test_checker_manager.py
index 50f4084..2a6998e 100644
--- a/tests/unit/test_checker_manager.py
+++ b/tests/unit/test_checker_manager.py
@@ -7,13 +7,12 @@ import pytest
 from flake8 import checker
 
 
-def style_guide_mock(**kwargs):
+def style_guide_mock():
     """Create a mock StyleGuide object."""
-    kwargs.setdefault('diff', False)
-    kwargs.setdefault('jobs', '4')
-    style_guide = mock.Mock()
-    style_guide.options = mock.Mock(**kwargs)
-    return style_guide
+    return mock.MagicMock(**{
+        'options.diff': False,
+        'options.jobs': '4',
+    })
 
 
 def _parallel_checker_manager():