cli: Add --list-files command line option

This option lists the files to lint by yamllint, taking into account `ignore`
and `yaml-files` configuration options.

docs/configuration.rst

@@ -136,6 +136,13 @@ directories, set ``yaml-files`` configuration option. The default is:
 The same rules as for ignoring paths apply (``.gitignore``-style path pattern,
 see below).
 
+If you need to know the exact list of files that yamllint would process,
+without really linting them, you can use ``--list-files``:
+
+.. code:: bash
+
+ yamllint --list-files .
+
 Ignoring paths
 --------------
 
@@ -220,6 +227,13 @@ or:
 
 .. note:: However, this is mutually exclusive with the ``ignore`` key.
 
+If you need to know the exact list of files that yamllint would process,
+without really linting them, you can use ``--list-files``:
+
+.. code:: bash
+
+ yamllint --list-files .
+
 Setting the locale
 ------------------
 

tests/test_cli.py

@@ -678,6 +678,39 @@ class CommandLineTestCase(unittest.TestCase):
         self.assertEqual(
             (ctx.returncode, ctx.stdout, ctx.stderr), (1, expected_out, ''))
 
+    def test_run_list_files(self):
+        with RunContext(self) as ctx:
+            cli.run(('--list-files', self.wd))
+        self.assertEqual(ctx.returncode, 0)
+        self.assertEqual(
+            sorted(ctx.stdout.splitlines()),
+            [os.path.join(self.wd, 'a.yaml'),
+             os.path.join(self.wd, 'c.yaml'),
+             os.path.join(self.wd, 'dos.yml'),
+             os.path.join(self.wd, 'empty.yml'),
+             os.path.join(self.wd, 'en.yaml'),
+             os.path.join(self.wd, 's/s/s/s/s/s/s/s/s/s/s/s/s/s/s/file.yaml'),
+             os.path.join(self.wd, 'sub/directory.yaml/empty.yml'),
+             os.path.join(self.wd, 'sub/ok.yaml'),
+             os.path.join(self.wd, 'warn.yaml')]
+        )
+
+        config = '{ignore: "*.yml", yaml-files: ["*.*"]}'
+        with RunContext(self) as ctx:
+            cli.run(('--list-files', '-d', config, self.wd))
+        self.assertEqual(ctx.returncode, 0)
+        self.assertEqual(
+            sorted(ctx.stdout.splitlines()),
+            [os.path.join(self.wd, 'a.yaml'),
+             os.path.join(self.wd, 'c.yaml'),
+             os.path.join(self.wd, 'en.yaml'),
+             os.path.join(self.wd, 'no-yaml.json'),
+             os.path.join(self.wd, 's/s/s/s/s/s/s/s/s/s/s/s/s/s/s/file.yaml'),
+             os.path.join(self.wd, 'sub/directory.yaml/not-yaml.txt'),
+             os.path.join(self.wd, 'sub/ok.yaml'),
+             os.path.join(self.wd, 'warn.yaml')]
+        )
+
 
 class CommandLineConfigTestCase(unittest.TestCase):
     def test_config_file(self):

yamllint/cli.py

@@ -157,6 +157,8 @@ def run(argv=None):
     config_group.add_argument('-d', '--config-data', dest='config_data',
                               action='store',
                               help='custom configuration (as YAML source)')
+    parser.add_argument('--list-files', action='store_true', dest='list_files',
+                        help='list files to lint and exit')
     parser.add_argument('-f', '--format',
                         choices=('parsable', 'standard', 'colored', 'github',
                                  'auto'),
@@ -207,6 +209,12 @@ def run(argv=None):
     if conf.locale is not None:
         locale.setlocale(locale.LC_ALL, conf.locale)
 
+    if args.list_files:
+        for file in find_files_recursively(args.files, conf):
+            if not conf.is_file_ignored(file):
+                print(file)
+        sys.exit(0)
+
     max_level = 0
 
     for file in find_files_recursively(args.files, conf):