Fix bug where pressing home on empty tag field crashes the program.

[libklein]

Fix bug where pressing home on empty tag field crashes the program.

Bug is caused by https://github.com/libklein/keepassxc/blob/develop/src/gui/tag/TagsEdit.cpp#L340. The currentText().isEmpty() allows to invalidate the invariant if the current (and only) tag is empty. In this case, tags is resized to 0 (the only tag is erased) and the program crashes as currentText() accessed in https://github.com/libklein/keepassxc/blob/develop/src/gui/tag/TagsEdit.cpp#L504 fails as the tags list is now empty (https://github.com/libklein/keepassxc/blob/develop/src/gui/tag/TagsEdit.cpp#L387).

Fixes: #11344

• ✅ Bug fix (non-breaking change that fixes an issue)

[libklein]

I've attempted to do some basic refactoring of the class. I've moved responsibility for keeping track of the current item, as well as maintaining the invariant into a dedicated "TagManager" class. This class avoids the index-tracking issues by using a QLinkedList rather than a QList, that we way never invalidate any iterators.

I've further attempted to have a clear split in responsibility between Impl and TagsEdit. Impl contains the tag handling logic, TagsEdit listens to events and calls Impl functions accordingly. I suggest merging Impl and TagsEdit, the only reason for having Impl in the first place was, I assume, to have a stable header API (PImpl).

I've further fixed a few minor bugs in the implementation:

• There was a corner case where an empty tag could be rendered when TagsEdit went out of focus with an empty tag selected
• Scrollbars were not updated after removing a tag
• Tags were not re-rendered (and re-layouted!) when ";" is pressed on an empty tag.

There is still a bug with rendering - the height hint of the textbox is wrong on first render - and a bit of cleanup needs to be done. I'd however like to get feedback on the general approach before polishing.

Another open question is the behavior of typing ";", which currently finishes editing the current tag. I think it's a bit unintuitive that this always finishes the current tag, regardless of cursor position. I'd expect the tag to be split if I type ";" in the middle of a tag.

What do you think? Any idea why the initial height hint may be off?

[droidmonkey]

Thank you for this work! I do agree that typing a ; or , should cause the tags to be split instead of ending typing immediately. But what about pressing space, that also ends tag typing. That could also help with pasting tag strings.