Look for per-project configuration file in parent directories

Inspired be ESLint's search, it looks for configuration files in all
parent directories up until it reaches the user's home or root.

closes #571

docs/configuration.rst

@@ -15,7 +15,8 @@ If ``-c`` is not provided, yamllint will look for a configuration file in the
 following locations (by order of preference):
 
 - a file named ``.yamllint``, ``.yamllint.yaml``, or ``.yamllint.yml`` in the
-  current working directory
+  current working directory, or a parent directory. The search for this file is
+  terminated at the user's home, or the root.
 - a filename referenced by ``$YAMLLINT_CONFIG_FILE``, if set
 - a file named ``$XDG_CONFIG_HOME/yamllint/config`` or
   ``~/.config/yamllint/config``, if present

tests/test_cli.py

@@ -734,3 +734,27 @@ def test_config_file(self):
 
                 self.assertEqual((ctx.returncode, ctx.stdout, ctx.stderr),
                                  (0, '', ''))
+
+    def test_parent_config_file(self):
+        workspace = { 'a/b/c/d/e/f/g/a.yml': 'hello: world\n' }
+        conf = ('---\n'
+                'extends: relaxed\n')
+
+        for conf_file in ('.yamllint', '.yamllint.yml', '.yamllint.yaml'):
+            with self.subTest(conf_file):
+                with temp_workspace(workspace):
+                    with RunContext(self) as ctx:
+                        os.chdir('a/b/c/d/e/f')
+                        cli.run(('-f', 'parsable', '.'))
+
+                self.assertEqual((ctx.returncode, ctx.stdout, ctx.stderr),
+                                 (0, './g/a.yml:1:1: [warning] missing document '
+                                     'start "---" (document-start)\n', ''))
+
+                with temp_workspace({**workspace, **{conf_file: conf}}):
+                    with RunContext(self) as ctx:
+                        os.chdir('a/b/c/d/e/f')
+                        cli.run(('-f', 'parsable', '.'))
+
+                self.assertEqual((ctx.returncode, ctx.stdout, ctx.stderr),
+                                 (0, '', ''))

yamllint/cli.py

@@ -140,6 +140,18 @@ def show_problems(problems, file, args_format, no_warn):
 
     return max_level
 
+def find_project_config(path='.'):
+
+    for filename in [ '.yamllint', '.yamllint.yaml', '.yamllint.yml' ]:
+        file = os.path.join(path, filename)
+        if os.path.isfile(file):
+            return file
+
+    if os.path.abspath(path) == os.path.abspath(os.path.expanduser('~')):
+        return False
+    if os.path.abspath(path) == os.path.abspath('/'):
+        return False
+    return find_project_config(path=os.path.join(path, '..'))
 
 def run(argv=None):
     parser = argparse.ArgumentParser(prog=APP_NAME,
@@ -192,12 +204,8 @@ def run(argv=None):
             conf = YamlLintConfig(content=args.config_data)
         elif args.config_file is not None:
             conf = YamlLintConfig(file=args.config_file)
-        elif os.path.isfile('.yamllint'):
-            conf = YamlLintConfig(file='.yamllint')
-        elif os.path.isfile('.yamllint.yaml'):
-            conf = YamlLintConfig(file='.yamllint.yaml')
-        elif os.path.isfile('.yamllint.yml'):
-            conf = YamlLintConfig(file='.yamllint.yml')
+        elif find_project_config():
+            conf = YamlLintConfig(file=find_project_config())
         elif os.path.isfile(user_global_config):
             conf = YamlLintConfig(file=user_global_config)
         else: