Bug 1592558, add support for extension parsers

This allows us to implement support for niche formats without
bothering about dependencies and m-c vendoring etc.

I'm looking at you, .lang.

Differential Revision: https://phabricator.services.mozilla.com/D51092

compare_locales/parser/__init__.py

@@ -54,6 +54,14 @@ def getParser(path):
     for item in __constructors:
         if re.search(item[0], path):
             return item[1]
+    try:
+        from pkg_resources import iter_entry_points
+        for entry_point in iter_entry_points('compare_locales.parsers'):
+            p = entry_point.resolve()()
+            if p.use(path):
+                return p
+    except (ImportError, IOError):
+        pass
     raise UserWarning("Cannot find Parser")
 
 

compare_locales/tests/test_parser.py

@@ -3,6 +3,7 @@
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 from __future__ import absolute_import
+import pkg_resources
 import shutil
 import tempfile
 import textwrap
@@ -87,3 +88,31 @@ class TestUniversalNewlines(unittest.TestCase):
         self.assertEqual(
             self.parser.ctx.contents,
             'one\ntwo\nthree\n')
+
+
+class TestPlugins(unittest.TestCase):
+    def setUp(self):
+        self.old_working_set_state = pkg_resources.working_set.__getstate__()
+        distribution = pkg_resources.Distribution(__file__)
+        entry_point = pkg_resources.EntryPoint.parse(
+            'test_parser = compare_locales.tests.test_parser:DummyParser',
+            dist=distribution
+        )
+        distribution._ep_map = {
+            'compare_locales.parsers': {
+                'test_parser': entry_point
+            }
+        }
+        pkg_resources.working_set.add(distribution)
+
+    def tearDown(self):
+        pkg_resources.working_set.__setstate__(self.old_working_set_state)
+
+    def test_dummy_parser(self):
+        p = parser.getParser('some/weird/file.ext')
+        self.assertIsInstance(p, DummyParser)
+
+
+class DummyParser(parser.Parser):
+    def use(self, path):
+        return path.endswith('weird/file.ext')