as2.link_tags: add class="mention" for Mention tags

see snarfed/bridgy-fed#887 (comment)

README.md

@@ -297,6 +297,7 @@ Standardize function and method names in all modules to `to_as1`, `from_as`, etc
     * Handle other types of tags better, eg non-standard `Hashtag` and inner `tag` field for name.
     * Bug fix for videos, `mimeType` goes in outer object, not in `stream`.
     * Bug fix for `to`/`cc` with mixed dict and string elements.
+  * `link_tags`: add `class="mention"` for `Mention` tags ([bridgy-fed/#887](https://github.com/snarfed/bridgy-fed/issues/887#issuecomment-2452141758)).
 * `atom`:
   * `atom_to_activity/ies`: Get URL from `link` for activities as well as objects. ([Thanks @imax9000!](https://github.com/snarfed/granary/issues/752))
 * `bluesky`:

granary/as2.py

@@ -752,12 +752,16 @@ def link_tags(obj):
   linked = ''
   for tag in tags:
     url = tag.get('href') or tag.get('url')
+    # Mastodon seems to need class="mention" to convert a mention link to point
+    # to the local instance's view of the remote actor profile
+    # https://github.com/snarfed/bridgy-fed/issues/887#issuecomment-2452141758
+    cls = 'class="mention" ' if tag.get('type') == 'Mention' else ''
     start = tag['startIndex']
     if start < last_end:
       logger.warning(f'tag indices overlap! skipping {url}')
       continue
     end = start + tag['length']
-    linked = f"{linked}{orig[last_end:start]}<a href=\"{url}\">{orig[start:end]}</a>"
+    linked = f"{linked}{orig[last_end:start]}<a {cls}href=\"{url}\">{orig[start:end]}</a>"
     last_end = end
     obj['content_is_html'] = True
     del tag['startIndex']

granary/tests/test_as2.py

@@ -3,6 +3,7 @@
 Most of the tests are in testdata/. This is just a few things that are too small
 for full testdata tests.
 """
+import copy
 from oauth_dropins.webutil import testutil
 
 from .. import as2
@@ -600,11 +601,11 @@ def test_link_tags(self):
     self.assert_equals('foo\nbar\nbaz', obj['content'])
 
     # with indices, should link and then remove indices
-    obj['tag'] = [
+    tags_with_indices = [
       {'href': 'http://bar', 'startIndex': 4, 'length': 3},
       {'url': 'http://baz', 'startIndex': 8, 'length': 3},
     ]
-
+    obj['tag'] = copy.deepcopy(tags_with_indices)
     as2.link_tags(obj)
     self.assert_equals({
       'content': """\
@@ -619,6 +620,29 @@ def test_link_tags(self):
       ],
     }, obj)
 
+    # Mention tag should include class="mention"
+    obj = {
+      'content': 'foo\nbar\nbaz',
+      'tag': [
+        {'href': 'http://bar', 'startIndex': 4, 'length': 3, 'type': 'Mention'},
+        {'url': 'http://baz', 'startIndex': 8, 'length': 3},
+      ],
+    }
+    as2.link_tags(obj)
+    self.assert_equals({
+      'content': """\
+foo
+<a class="mention" href="http://bar">bar</a>
+<a href="http://baz">baz</a>
+""",
+      'content_is_html': True,
+      'tag': [
+        {'href': 'http://bar', 'type': 'Mention'},
+        {'url': 'http://baz'},
+      ],
+    }, obj)
+
+
   def test_is_server_actor(self):
     self.assertFalse(as2.is_server_actor({}))