content: Support the new class of channel wildcard mentions

For channel wildcard mentions, the class in the corresponding HTML used
to be the same as the user mentions (class="user-mention"), but now
there's an additional class added. Now it looks like the following:
class="user-mention channel-wildcard-mention".

Fixes: zulip#1064

Author: sm-sayedi

lib/model/content.dart

@@ -808,10 +808,12 @@ class _ZulipContentParser {
   }
 
   static final _userMentionClassNameRegexp = () {
-    // This matches a class `user-mention` or `user-group-mention`,
-    // plus an optional class `silent`, appearing in either order.
-    const mentionClass = r"user(?:-group)?-mention";
-    return RegExp("^(?:$mentionClass(?: silent)?|silent $mentionClass)\$");
+    // This matches the classes `user-mention`, `user-group-mention`,
+    // or `user-mention channel-wildcard-mention`, plus an optional
+    // class `silent`, appearing in either order.
+    const mentionClass = r"user(?:-group)?-mention|"
+                          "(?:user-mention channel-wildcard-mention)";
+    return RegExp("^(?:$mentionClass)(?: silent)?|silent (?:$mentionClass)\$");
   }();
 
   static final _emojiClassNameRegexp = () {

test/model/content_test.dart

@@ -139,6 +139,48 @@ class ContentExample {
     '<p><span class="silent user-group-mention" data-user-group-id="186">test-empty</span></p>',
     const UserMentionNode(nodes: [TextNode('test-empty')]));
 
+  static final channelWildcardMentionPlain = ContentExample.inline(
+    'plain channel wildcard @-mention',
+    "@**all**",
+    expectedText: '@all',
+    '<p><span class="user-mention channel-wildcard-mention" data-user-id="*">@all</span></p>',
+    const UserMentionNode(nodes: [TextNode('@all')]));
+
+  static final channelWildcardMentionSilent = ContentExample.inline(
+    'silent channel wildcard @-mention',
+    "@_**everyone**",
+    expectedText: 'everyone',
+    '<p><span class="user-mention channel-wildcard-mention silent" data-user-id="*">everyone</span></p>',
+    const UserMentionNode(nodes: [TextNode('everyone')]));
+
+  static final channelWildcardMentionSilentClassOrderReversed = ContentExample.inline(
+    'silent channel wildcard @-mention, class order reversed',
+    "@_**channel**", // (hypothetical server variation)
+    expectedText: 'channel',
+    '<p><span class="silent user-mention channel-wildcard-mention" data-user-id="*">channel</span></p>',
+    const UserMentionNode(nodes: [TextNode('channel')]));
+
+  static final legacyChannelWildcardMentionPlain = ContentExample.inline(
+    'legacy plain channel wildcard @-mention',
+    "@**channel**",
+    expectedText: '@channel',
+    '<p><span class="user-mention" data-user-id="*">@channel</span></p>',
+    const UserMentionNode(nodes: [TextNode('@channel')]));
+
+  static final legacyChannelWildcardMentionSilent = ContentExample.inline(
+    'legacy silent channel wildcard @-mention',
+    "@_**stream**",
+    expectedText: 'stream',
+    '<p><span class="user-mention silent" data-user-id="*">stream</span></p>',
+    const UserMentionNode(nodes: [TextNode('stream')]));
+
+  static final legacyChannelWildcardMentionSilentClassOrderReversed = ContentExample.inline(
+    'legacy silent channel wildcard @-mention, class order reversed',
+    "@_**all**", // (hypothetical server variation)
+    expectedText: 'all',
+    '<p><span class="silent user-mention" data-user-id="*">all</span></p>',
+    const UserMentionNode(nodes: [TextNode('all')]));
+
   static final emojiUnicode = ContentExample.inline(
     'Unicode emoji, encoded in span element',
     ":thumbs_up:",
@@ -1013,7 +1055,13 @@ void main() {
     testParseExample(ContentExample.groupMentionSilent);
     testParseExample(ContentExample.groupMentionSilentClassOrderReversed);
 
-    // TODO test wildcard mentions
+    testParseExample(ContentExample.channelWildcardMentionPlain);
+    testParseExample(ContentExample.channelWildcardMentionSilent);
+    testParseExample(ContentExample.channelWildcardMentionSilentClassOrderReversed);
+
+    testParseExample(ContentExample.legacyChannelWildcardMentionPlain);
+    testParseExample(ContentExample.legacyChannelWildcardMentionSilent);
+    testParseExample(ContentExample.legacyChannelWildcardMentionSilentClassOrderReversed);
   });
 
   testParseExample(ContentExample.emojiUnicode);

test/widgets/content_test.dart

@@ -626,6 +626,12 @@ void main() {
     testContentSmoke(ContentExample.userMentionSilent);
     testContentSmoke(ContentExample.groupMentionPlain);
     testContentSmoke(ContentExample.groupMentionSilent);
+    testContentSmoke(ContentExample.channelWildcardMentionPlain);
+    testContentSmoke(ContentExample.channelWildcardMentionSilent);
+    testContentSmoke(ContentExample.channelWildcardMentionSilentClassOrderReversed);
+    testContentSmoke(ContentExample.legacyChannelWildcardMentionPlain);
+    testContentSmoke(ContentExample.legacyChannelWildcardMentionSilent);
+    testContentSmoke(ContentExample.legacyChannelWildcardMentionSilentClassOrderReversed);
 
     UserMention? findUserMentionInSpan(InlineSpan rootSpan) {
       UserMention? result;