Add join and leave messages

[tox-user]

Adds messages that notify when user joins or leaves group chat or changes their name. Implements #4128.

Current issues:

• when user joins a non empty group chat they will always get a join message for every participant at once
• every time someone joins a group that we are in, we don't see their user name at first. Instead we see "Tox User" as their name. A few seconds later the name changes to their real name, which creates additional message

I am not sure how to fix them yet.

Depends on TokTok/c-toxcore#819

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This change is 

[iphydf]

Hi tox-user, we're working on a change that slightly changes the group chat api. Can we discuss somewhere?

[tox-user]

Hi @iphydf could you add me on Tox? You will find my ID in my profile.

[tox-user]

This is ready for testing and review now.

[Diadlo]

1. It doesn't works
2. If you move all code in if (oldPeersList.length() > 0) (with if itself) after peer filling but before emit it will work
3. And after fix(group): Show correct count of user on first creation #4978 merge (because otherwise you haven't any messages on first peer come)
4. And since we show friend alias if we have peer as friend, probably you shouldn't emit peerNameChanged if friend found (probably, we should show both and correct handle it, but feel free to leave it now)

[tox-user]

It's true that it doesn't work in this scenario:

1. Client #1 creates a group and invites client #2.
2. Client #2 joins.
3. Client #1 will not receive the join notification.

PR #4978 itself doesn't fix it. It makes it more strange, because then client #2 gets duplicate join notifications.

[Diadlo]

@tox-user Did you move if (oldPeersList.length() > 0)?

[tox-user]

That helped, but I get a notification spam when I join a bigger existing group.

[Talkless]

Review status: 0 of 4 files reviewed at latest revision, all discussions resolved, some commit checks failed.

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src/model/group.cpp, line 53 at r1 (raw file):

    // which is later changed to their real name. Because of that we treat everyone
    // who changed the name from empty to non empty as a newly joined user
    if (name != peers[peerId]) {

Same peers[peerId] lookup is performed two-three times, could it be avoided?

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src/model/group.cpp, line 109 at r1 (raw file):

    if (oldPeersList.length() > 0) {
        // peers that have joined
        for (int i = 0; i < peers.length(); i++) {

is int i index really needed here? As far as I can see, ranged-based for loop could work?

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src/model/group.cpp, line 118 at r1 (raw file):

        // peers that have left
        for (int i = 0; i < oldPeersList.length(); i++) {

range-based for loop instead?

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src/widget/widget.cpp, line 1841 at r1 (raw file):

    const QString message = tr("%1 has joined the chat");

    Group* g = GroupList::findGroup(groupnumber);

Group* const g? Or maybe even const Group* const g (if getId() is const)?

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src/widget/widget.cpp, line 1855 at r1 (raw file):

    const QString message = tr("%1 has left the chat");

    Group* g = GroupList::findGroup(groupnumber);

same constsness.

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src/widget/widget.cpp, line 1869 at r1 (raw file):

    const QString message = tr("%1 is now known as %2");

    Group* g = GroupList::findGroup(groupnumber);

same constness

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Comments from Reviewable

[tox-user]

@Talkless thanks for reviewing, but unfortunately this PR doesn't work anymore, because of #4978. I don't know how to get it working again, so I've decided to leave it and move on to other things. Maybe I will take a look at it again some time in the future or someone else will pick it up.