Bug 1366298 - Skip SelectExpression in PLURALS for one plural category (#27)

Languages with one plural category can have their translations migrated
directly to a single Pattern rather than a SelectExpression with one
variant.  This will only happen when the number of variants in the
legacy translation is also one.

This also adds tests for languages with more categories than en-US.

Author: stasm

fluent/migrate/transforms.py

@@ -236,6 +236,13 @@ def __call__(self, ctx):
         selector = evaluate(ctx, self.selector)
         variants = value.split(';')
         keys = ctx.plural_categories
+
+        # A special case for languages with one plural category. We don't need
+        # to insert a SelectExpression at all for them.
+        if len(keys) == len(variants) == 1:
+            variant, = variants
+            return evaluate(ctx, self.foreach(variant))
+
         last_index = min(len(variants), len(keys)) - 1
 
         def createVariant(zipped_enum):

tests/migrate/test_plural.py

@@ -15,7 +15,8 @@
 
 
 class MockContext(unittest.TestCase):
-    # Static categories corresponding to en-US.
+    maxDiff = None
+    # Plural categories corresponding to English (en-US).
     plural_categories = ('one', 'other')
 
     def get_source(self, path, key):
@@ -142,5 +143,81 @@ def test_plural_replace(self):
         )
 
 
+@unittest.skipUnless(PropertiesParser, 'compare-locales required')
+class TestOneCategory(MockContext):
+    # Plural categories corresponding to Turkish (tr).
+    plural_categories = ('other',)
+
+    def setUp(self):
+        self.strings = parse(PropertiesParser, '''
+            deleteAll=#1 indirme silinsin mi?
+        ''')
+
+        self.message = FTL.Message(
+            FTL.Identifier('delete-all'),
+            value=PLURALS(
+                'test.properties',
+                'deleteAll',
+                EXTERNAL_ARGUMENT('num'),
+                lambda text: REPLACE_IN_TEXT(
+                    text,
+                    {
+                        '#1': EXTERNAL_ARGUMENT('num')
+                    }
+                )
+            )
+        )
+
+    def test_no_select_expression(self):
+        self.assertEqual(
+            evaluate(self, self.message).to_json(),
+            ftl_message_to_json('''
+                delete-all = { $num } indirme silinsin mi?
+            ''')
+        )
+
+
+@unittest.skipUnless(PropertiesParser, 'compare-locales required')
+class TestManyCategories(MockContext):
+    # Plural categories corresponding to Polish (pl).
+    plural_categories = ('one', 'few', 'many', 'other')
+
+    def setUp(self):
+        self.strings = parse(PropertiesParser, '''
+            deleteAll=Usunąć plik?;Usunąć #1 pliki?;Usunąć #1 plików?
+        ''')
+
+        self.message = FTL.Message(
+            FTL.Identifier('delete-all'),
+            value=PLURALS(
+                'test.properties',
+                'deleteAll',
+                EXTERNAL_ARGUMENT('num'),
+                lambda text: REPLACE_IN_TEXT(
+                    text,
+                    {
+                        '#1': EXTERNAL_ARGUMENT('num')
+                    }
+                )
+            )
+        )
+
+    def test_too_few_variants(self):
+        # StringBundle's plural rule #9 used for Polish has three categories
+        # which is one fewer than the CLDR's. The migrated string will not have
+        # the [other] variant and [many] will be marked as the default.
+        self.assertEqual(
+            evaluate(self, self.message).to_json(),
+            ftl_message_to_json('''
+                delete-all =
+                    { $num ->
+                        [one] Usunąć plik?
+                        [few] Usunąć { $num } pliki?
+                       *[many] Usunąć { $num } plików?
+                    }
+            ''')
+        )
+
+
 if __name__ == '__main__':
     unittest.main()