remote-diff

name	remote-diff
description	Compare local branch changes against the remote branch to detect rebase/merge mistakes.
user-invocable-only	true
allowed-tools	Bash, Read, Glob, Grep, Agent
argument-hint	["base-branch"]

Remote Diff

Compare local branch changes against the remote branch to detect rebase/merge mistakes.

Step 1: Determine base branch

Determine the base branch in this order:

1. Use $ARGUMENTS if the user specifies a branch
2. Use the tracked parent from git config branch.$(git branch --show-current).parent, if set and it still resolves to a commit
3. Use bin/base-branch if the script exists and is executable
4. Fall back to develop

Step 2: Check prerequisites

Verify the upstream tracking branch exists:

git rev-parse --verify @{u}

If this fails, report that there's no remote branch to compare against and stop. The user needs to push their branch first.

Ensure the tmp directory exists:

mkdir -p tmp

Step 3: Generate and compare diffs

Fetch the latest remote refs, generate both diffs with zero context lines and ignoring whitespace changes, strip metadata lines, then compare:

git fetch origin

git diff -b --unified=0 <base-branch>...HEAD > tmp/local_branch_diff.patch
git diff -b --unified=0 origin/<base-branch>...@{u} > tmp/remote_branch_diff.patch

grep -v -E '^(index |@@ |diff --git)' tmp/local_branch_diff.patch > tmp/local_stripped.patch
grep -v -E '^(index |@@ |diff --git)' tmp/remote_branch_diff.patch > tmp/remote_stripped.patch

diff tmp/local_stripped.patch tmp/remote_stripped.patch > tmp/diff_comparison.patch || true

Step 4: Analyze results

Read tmp/diff_comparison.patch.

If it's empty, report: Clean rebase — no issues detected. The local and remote branches make identical code changes relative to the base branch.

If there are differences, read the relevant source files for context and report:

Interpreting differences

Any difference warrants review. Read the source files to assess each one.

Signs of trouble:

• A + line present in the remote diff but missing from local → an addition was lost during rebase
• A - line present in the remote diff but missing from local → a deletion was lost, meaning removed code came back
• Lines present only in the local diff could be conflict resolution or accidental — verify by reading the code

Report format

For each difference:

• What changed — which file and what code differs
• Remote version — what the remote branch had
• Local version — what the local branch has
• Assessment — whether this looks intentional (e.g., correct conflict resolution adapting to renamed code) or suspicious (e.g., lost code, accidental reversion, duplicated changes)

Summary

• Overall assessment: clean rebase or needs attention
• Any lost or accidentally reverted changes
• Any suspicious conflict resolutions

Step 5: Clean up

rm -f tmp/local_branch_diff.patch tmp/remote_branch_diff.patch tmp/local_stripped.patch tmp/remote_stripped.patch tmp/diff_comparison.patch