[Feature] Combine all commits in a branch and display a unified diff per changed file

[leoluz]

First of all thank you for your work and congrats for your amazing plugin!

Use-case: As reviewer I would like to see all diffs from different commits in a branch combined in a single view so I can easily reason about how the final state will look like once merged.

Longer explanation:
PRs are often composed by multiple commits. While we progress in the review, contributors will modify their previous commits. By looking at individual commits is very challenging to understand how the final state of a given file is going to be. To address this problem, it would be great if this plugin could combine diffs from all commits in a given file in a given branch.

Sorry if this was already discussed in the past. I quickly looked at the opened issues but didn't find anything at first.

[sindrets]

The feature request for unified diffs is tracked here: #39.

Use-case: As reviewer I would like to see all diffs from different commits in a branch combined in a single view so I can easily reason about how the final state will look like once merged.

If I understand you correctly you want to diff the head of a feature branch against it's merge-base? This is already possible. You can compare the state between any two Git revs with :DiffviewOpen {REV1}..{REV2}. Git also has a shorthand for describing the range between any rev and it's merge-base - the triple-dot notation:

:DiffviewOpen origin/HEAD...HEAD

This is described under :h :DiffviewOpen, and also in USAGE.md.