android: Notification grouping should treat topics case-insensitively

[chrisbobbe]

We use Android's "inbox style" notifications (this was #128 / PR #718) to group notifications by conversation.

For channel messages, this means grouping messages by topic. Topics in Zulip are meant to be case-insensitive, so we should ignore case for that grouping. For example, messages with the topic "move to Zulip" or the topic "move to zulip" should all be grouped together.¹

Other issues where we should be treating topics case-insensitively but we're not:

• Case-insensitive topics in unreads data #980
• Extra recipient header when topic changes case #739

See our notification-display code for getting a message's "conversation key". It just takes the topic literally without normalizing it by case:

  static String _conversationKey(MessageFcmMessage data, String groupKey) {
    final conversation = switch (data.recipient) {
      FcmMessageChannelRecipient(:var streamId, :var topic) => 'stream:$streamId:$topic',
      FcmMessageDmRecipient(:var allRecipientIds) => 'dm:${allRecipientIds.join(',')}',
    };
    return '$groupKey|$conversation';
  }

Footnotes

1. As they are in the message list in the web app. By using "Copy link to message", you can see that this and this message have those topics that only differ by case. But they both appear in the message list as though they both have topic "move to Zulip". ↩

[chrisbobbe]

See our notification-display code for getting a message's "conversation key". It just takes the topic literally without normalizing it by case:

(I assume the server isn't normalizing it for us.)

[timabbott]

Generally, the server always tries to preserve case when passing data around, since you often do want to display with the case the user entered, even when normalizing for comparisons. So doing .lower() needs to happen in clients where they are trying to group messages by topic, rather than display topics.