Git advanced merging

Advanced Git Merging

Conflict Marker Style

Default hides the common ancestor. Show it:

git config --global merge.conflictStyle zdiff3   # git 2.35+; else diff3
git checkout --conflict=diff3 path               # re-render existing conflict

Markers become <<<ours / ||| base / === / theirs >>> — resolution is far easier.

Side-Picking

git checkout --ours path
git checkout --theirs path
git add path

During rebase, ours/theirs swap: "theirs" = the commits being replayed.

Strategy (-s) vs Strategy Option (-X)

• Strategy (-s) picks the algorithm: ort (default), recursive, resolve, octopus, ours, subtree.
• Option (-X) tunes a strategy. -X ours only breaks ties; non-conflicting changes still merge.

git merge -X ours feature           # merge all, prefer ours on conflict
git merge -s ours feature           # fake-merge: record, keep tree unchanged
git merge -X ignore-all-space feature
git merge -X patience feature       # better diff for reordered blocks

-s ours says "we abandon their work but don't want future merges replaying it."

Inspecting

git ls-files -u                     # stages 1=base, 2=ours, 3=theirs
git show :1:f > base; git show :2:f > ours; git show :3:f > theirs
git merge-file -p ours base theirs > resolved
git log --merge -p path             # commits on either side touching file
git log --left-right HEAD...MERGE_HEAD

Abort

git merge --abort                   # before committing
git reset --merge                   # equivalent

Undoing a Completed Merge

Local only: git reset --hard ORIG_HEAD

Already pushed: git revert -m 1 <merge-sha> (keep mainline, drop feature side).

Gotcha: after revert -m 1, re-merging the same branch pulls only new commits — Git thinks the rest is already merged. Fix:

git revert <revert-commit>          # un-revert
git merge feature                   # clean re-merge

Pitfalls

• No -s theirs exists; do -s ours on the other branch then merge back.
• Octopus strategy refuses to auto-resolve conflicts.
• For recurring conflicts, enable rerere.