Reviewing a branch: `git diff` wants three dots, `git log` wants two
Same task — "show me what this branch changed" — but the two tools take opposite dot conventions. Get it backwards and your review fills with commits the author never touched.
The diff: use three dots
git diff origin/main...HEAD
Three-dot diff is git diff $(git merge-base origin/main HEAD) HEAD — it diffs against the branch point, not the tip of main. That's exactly what you want: the author's delta and nothing else.
The nice property: it's immune to origin/main moving forward. New commits landing on main after the branch point aren't ancestors of HEAD, so they don't shift the merge-base. The diff stays clean.
The trap is a stale base, not a newer one. If your local main is older than the branch point, the merge-base slides back to an older ancestor and the diff swallows unrelated upstream commits — making the author look like they changed far more than they did. So fetch first:
git fetch origin
git diff origin/main...HEAD
Want to see the branch point itself? git merge-base origin/main HEAD.
The log: use two dots
git log origin/main..HEAD
Two-dot log = commits reachable from HEAD but not from origin/main = the branch's own commits, exactly.
Don't reach for three dots here out of habit — git log A...B is the symmetric difference, so it also lists the commits main picked up that HEAD doesn't have. That's the noise you were trying to avoid.
So: diff three-dot, log two-dot. Different tools, opposite defaults, same job.