FilenameBear.py: Enable default naming convention

Add default naming conventions that are widely accepted for
languages like java, javascript and python. Add 'auto' option
to predict the file naming convention.

Closes coala#1083

bears/general/FilenameBear.py

@@ -19,14 +19,22 @@ class FilenameBear(LocalBear):
                           'snake': to_snakecase,
                           'space': to_spacecase}
 
+    _language_naming_convention = {
+                                   '.java': 'pascal',
+                                   '.js': 'kebab',
+                                   '.py': 'snake',
+                                  }
+
     def run(self, filename, file,
-            file_naming_convention: str='snake',
+            file_naming_convention: str=None,
             ignore_uppercase_filenames: bool=True):
         """
         Checks whether the filename follows a certain naming-convention.
 
         :param file_naming_convention:
             The naming-convention. Supported values are:
+            - ``auto`` to guess the correct convention. Defaults to ``snake``
+            if the correct convention cannot be guessed.
             - ``camel`` (``thisIsCamelCase``)
             - ``kebab`` (``this-is-kebab-case``)
             - ``pascal`` (``ThisIsPascalCase``)
@@ -38,6 +46,23 @@ def run(self, filename, file,
         """
         head, tail = os.path.split(filename)
         filename_without_extension, extension = os.path.splitext(tail)
+
+        if file_naming_convention is None:
+            self.warn('Please specify a file naming convention explicitly'
+                      ' or use "auto".')
+            file_naming_convention = 'auto'
+        else:
+            file_naming_convention = file_naming_convention.lower()
+
+        if file_naming_convention == 'auto':
+            if extension in self._language_naming_convention:
+                file_naming_convention = self._language_naming_convention[
+                    extension]
+            else:
+                self.warn('The file naming convention could not be guessed. '
+                          'Using the default "snake" naming convention.')
+                file_naming_convention = 'snake'
+
         try:
             new_name = self._naming_convention[file_naming_convention](
                 filename_without_extension)

tests/general/FilenameBearTest.py

@@ -21,14 +21,13 @@ def test_invalid_naming_convention(self):
 
         log = self.uut.message_queue.get(timeout=1)
         self.assertEqual(log.message,
-                         'Invalid file-naming-convention provided: INVALID')
+                         'Invalid file-naming-convention provided: invalid')
         self.assertEqual(log.log_level, LOG_LEVEL.ERROR)
 
     def test_snake_case(self):
+        self.section['file_naming_convention'] = 'snake'
         self.check_validity(self.uut, [''], filename='/Home/xyz/x_y.py')
         self.check_validity(self.uut, [''], filename='XYZ/__init__.py')
-
-        self.section['file_naming_convention'] = 'snake'
         self.check_validity(self.uut, [''], filename='/a/camCase', valid=False)
 
     def test_camel_case(self):
@@ -46,11 +45,12 @@ def test_kebab_case(self):
         self.check_validity(self.uut, [''], filename='/a/kebab-case')
 
     def test_pascal_case(self):
-        self.section['file_naming_convention'] = 'pascal'
-        self.check_validity(self.uut, [''], filename='/Home/xyz/x_y.py',
-                            valid=False)
-        self.check_validity(self.uut, [''], filename='XYZ/__Init__.py')
-        self.check_validity(self.uut, [''], filename='/a/PascalCase')
+        for convention in ('Pascal', 'pascal', 'PASCAL'):
+            self.section['file_naming_convention'] = convention
+            self.check_validity(self.uut, [''], filename='/Home/xyz/x_y.py',
+                                valid=False)
+            self.check_validity(self.uut, [''], filename='XYZ/__Init__.py')
+            self.check_validity(self.uut, [''], filename='/a/PascalCase')
 
     def test_space_case(self):
         self.section['file_naming_convention'] = 'space'
@@ -63,8 +63,58 @@ def test_space_case(self):
         self.check_validity(self.uut, [''], filename='/a/Space Case')
 
     def test_ignore_upper(self):
+        self.section['file_naming_convention'] = 'auto'
         self.check_validity(self.uut, [''], filename='/LICENSE')
 
         self.section['ignore_uppercase_filenames'] = 'nope'
 
         self.check_validity(self.uut, [''], filename='/LICENSE', valid=False)
+
+    def test_default_naming_java(self):
+        self.section['file_naming_convention'] = 'auto'
+        self.check_validity(self.uut, [''], filename='/Home/xyz/x_y.java',
+                            valid=False)
+        self.check_validity(self.uut, [''], filename='/Home/xyz/x-y.java',
+                            valid=False)
+        self.check_validity(self.uut, [''], filename='/Home/xyz/x y.java',
+                            valid=False)
+        self.check_validity(self.uut, [''], filename='/Home/xyz/XY.java')
+
+    def test_default_naming_javascript(self):
+        self.section['file_naming_convention'] = 'auto'
+        self.check_validity(self.uut, [''], filename='/Home/xyz/x_y.js',
+                            valid=False)
+        self.check_validity(self.uut, [''], filename='/Home/xyz/x y.js',
+                            valid=False)
+        self.check_validity(self.uut, [''], filename='/Home/xyz/XY.js')
+        self.check_validity(self.uut, [''], filename='/Home/xyz/x-y.js')
+
+    def test_default_file_naming_python(self):
+        self.section['file_naming_convention'] = 'auto'
+        self.check_validity(self.uut, [''], filename='/Home/xyz/x_y.py')
+        self.check_validity(self.uut, [''], filename='XYZ/__init__.py')
+        self.check_validity(self.uut, [''], filename='/a/x y.py', valid=False)
+
+    def test_none_file_naming_convention_warning(self):
+        self.uut.execute('filename', [])
+
+        # Automatic bear messages we want to ignore.
+        self.uut.message_queue.get()
+
+        log = self.uut.message_queue.get(timeout=1)
+        self.assertEqual(log.message,
+                         'Please specify a file naming convention explicitly'
+                         ' or use "auto".')
+        self.check_validity(self.uut, [''], filename='/Home/xyz/x_y.py')
+
+    def test_auto_file_naming_convention_warning(self):
+        self.section['file_naming_convention'] = 'auto'
+        self.uut.execute('filename.xyz', [])
+
+        # Automatic bear messages we want to ignore.
+        self.uut.message_queue.get()
+
+        log = self.uut.message_queue.get(timeout=1)
+        self.assertEqual(log.message,
+                         'The file naming convention could not be guessed. '
+                         'Using the default "snake" naming convention...')