Extended Code Review functionality

[Paul Chown]

I was thinking this morning about code reviews. We often have larger refactorings that touch lots of files, often with trivial changes, and it's hard to find time to go through the whole thing in one sitting without being interrupted. After you've been interrupted, it's also hard to know where you were.

How about adding an additional space for code reviews. For simple changes it's OK to just approve directly and comment directly in the PR (as now), but for larger PRs it would be really nice to be able to say 'start code review' and then enter a private space where I can:

• mark files as 'unreviewed', 'approved', or tag with custom labels ('Cool!', 'Huh?') and colours
• filter the view by label (show all, only show unreviewed files, only show 'Huh?' files)
• comment/annotate locally without notifying other users

The fact that a code review has been started would also show up in the PR, so if someone has already started the review of a large PR other reviewers can see that and avoid duplicate effort.

The state can be defined by file and head revision, so if the PR is updated then modified files revert to 'unreviewed'.

On completion, any open comments can be transferred to the main PR and the review status updated appropriately.

It seems like this should fit with a lot of the existing functionality and interface components, and would help enormously to deal with big PRs as 'trivial' changes can be quickly filtered out, progress is persisted through interruptions, and duplicate work is avoided.