Improve keyword merging

Author: tomasr8

Lib/test/test_tools/test_i18n.py

@@ -528,15 +528,22 @@ def test_process_keywords(self):
             (['foo', 'foo:1,2'], True),
             (['foo'], False),
             (['_:1,2', '_:1c,2,3', 'pgettext'], False),
+            # Duplicate entries
+            (['foo', 'foo'], True),
+            (['_'], False)
         )
         expected = (
             {'foo': [{'msgid': 0}]},
             {'_': [{'msgid': 0, 'msgid_plural': 1}]},
             {'foo': [{'msgid': 0}, {'msgid': 0, 'msgid_plural': 1}]},
             default_keywords | {'foo': [{'msgid': 0}]},
             default_keywords | {'_': [{'msgid': 0, 'msgid_plural': 1},
-                                      {'msgctxt': 0, 'msgid': 1, 'msgid_plural': 2}],
-                                'pgettext': [{'msgid': 0}]},
+                                      {'msgctxt': 0, 'msgid': 1, 'msgid_plural': 2},
+                                      {'msgid': 0}],
+                                'pgettext': [{'msgid': 0},
+                                             {'msgctxt': 0, 'msgid': 1}]},
+            {'foo': [{'msgid': 0}]},
+            default_keywords,
         )
         for (keywords, no_default_keywords), expected in zip(inputs, expected):
             with self.subTest(keywords=keywords,

Tools/i18n/pygettext.py

@@ -391,7 +391,8 @@ def unparse_spec(name, spec):
 
 
 def process_keywords(keywords, *, no_default_keywords):
-    custom_keywords_list = [parse_spec(spec) for spec in keywords]
+    custom_keywords_list = [parse_spec(spec) for
+                            spec in dict.fromkeys(keywords)]
     custom_keywords = {}
     for name, spec in custom_keywords_list:
         if name not in custom_keywords:
@@ -401,9 +402,13 @@ def process_keywords(keywords, *, no_default_keywords):
     if no_default_keywords:
         return custom_keywords
 
-    default_keywords = {name: [spec] for name, spec in DEFAULTKEYWORDS.items()}
     # custom keywords override default keywords
-    return default_keywords | custom_keywords
+    for name, spec in DEFAULTKEYWORDS.items():
+        if name not in custom_keywords:
+            custom_keywords[name] = []
+        if spec not in custom_keywords[name]:
+            custom_keywords[name].append(spec)
+    return custom_keywords
 
 
 @dataclass(frozen=True)