refact(shells): add support to Fish functions

Signed-off-by: Pablo Santiago Blum de Aguiar <scorphus@gmail.com>

tests/test_shells.py

@@ -78,6 +78,12 @@ class TestFish(object):
     def shell(self):
         return shells.Fish()
 
+    @pytest.fixture(autouse=True)
+    def Popen(self, mocker):
+        mock = mocker.patch('thefuck.shells.Popen')
+        mock.return_value.stdout.read.return_value = (b'funced\nfuncsave\ngrep')
+        return mock
+
     @pytest.mark.parametrize('before, after', [
         ('pwd', 'pwd'),
         ('ll', 'll')])  # Fish has no aliases but functions
@@ -98,7 +104,9 @@ class TestFish(object):
         assert shell.and_('foo', 'bar') == 'foo; and bar'
 
     def test_get_aliases(self, shell):
-        assert shell.get_aliases() == {}
+        assert shell.get_aliases() == {'funced': 'funced',
+                                       'funcsave': 'funcsave',
+                                       'grep': 'grep'}
 
 
 @pytest.mark.usefixtures('isfile')

thefuck/shells.py

@@ -97,6 +97,15 @@ class Fish(Generic):
                 "    end\n"
                 "end")
 
+    def get_aliases(self):
+        if not self._aliases:
+            proc = Popen('fish -ic functions', stdout=PIPE, stderr=DEVNULL,
+                         shell=True)
+            functions = proc.stdout.read().decode('utf-8').strip().split('\n')
+            self._aliases = dict((function, function) for function in functions)
+
+        return self._aliases
+
     def _get_history_file_name(self):
         return os.path.expanduser('~/.config/fish/fish_history')