You made a modification to the code. They made a conflicting modification. You want to know what they hell they were doing so you know how to rejig your edit. The normal tool to use here would be `git blame` but that just doesn't work. At least in any tool I have used.
If anyone knows of one where it does work I'd love to know!
git log -p HEAD...MERGE_HEAD --path/to/file
Another trick is doing multiple merges which each include fewer commits. Sometimes the problem is that you're just trying to merge too much at a time. The downside of this is that in files with a lot of churn you may have to deal with conflicts that you might otherwise not. So it's a bit of a two-edged sword.
I really hate that relative terminology. Call them "working copy", "merging commit" and "common ancestor" or something similarly absolute. And give me the revision/commit id's for each, so it's crystal clear in case I want to check up manually.
Not a dig on the vscode extension, but 3-way diff tools in general.
> And give me the revision/commit id's for each
It could show the branch names! `change on master`, `change on myfeature` or whatever.