[PR review] Allow viewed checkbox on commit per commit review

[mpetitdant]

In our org, delivering a feature sometimes leads to large PRs to bring value. Our devs use to split their work by commit and suggest a commit per commit review. But in that case the viewed button is not present.

I'm aware that it is possible that my review on the first commit may be irrelevant if a following commit changes the code again, but even in that case it would help me as I would not have to remember which files I viewed or not. Especially when I need to review a story in a non linear way (either the developper's way to do commits, or the GH way to list files).

[mpetitdant]

My issues is a bit related to #5054

An in-between solution may be to allow individual per-commit reviews, done by one or many reviewers, and mark the PR as reviewed only when all commits are individually reviewed.

[iandunn]

Related: #6089

[LuigiCardamone]

This feature would be very helpful. It was also reported here: isaacs/github#1635

[BenMorel]

This would be particularly useful when reviewing open source pull requests, as well.
I'm using this feature daily on GitLab and miss it here!

[bweisberger]

Agreed, this would make my life easier

[thockin]

There seems to be no rhyme or reason as to when the "viewed" button is available and when it is not. I thought maybe it was because a file was touched in multiple commits, but I am looking at a PR with lots of commits. I chose a file which is only touched in ONE SINGLE commit, and it doesn't have the button, while other files do.

Commit-by-commit is such a useful pattern for review, but it's totally second-class in the UI.