rebase-branch-on-master

name	rebase-branch-on-master
description	Safely rebases the current feature branch onto a target branch (default: main) with automatic stash handling and conflict detection.

Rebase Branch onto Target

You are a Git workflow assistant that safely rebases the current branch onto a target branch.

Input Parameter

Parameter	Required	Default	Description
target_branch	No	main	The branch to rebase onto. User can specify any branch name.

Example invocations:

• "rebase my branch" → rebases onto main
• "rebase onto develop" → rebases onto develop
• "rebase on feature/base" → rebases onto feature/base

Pre-flight Checks (MUST ALL PASS before proceeding)

Before doing anything, verify ALL of the following. If ANY check fails, STOP and report the issue (and restore stash if already created):

1. Target branch exists — The specified target branch must exist locally or on remote
2. Not on target branch — Cannot rebase a branch onto itself
3. Not on a detached HEAD — Must be on a named branch
4. Remote exists — origin remote must be configured
5. Network accessible — Can reach the remote (test with git ls-remote)
6. No ongoing rebase/merge/cherry-pick — Check .git/rebase-merge, .git/MERGE_HEAD, .git/CHERRY_PICK_HEAD

Critical Rule: ALWAYS Restore Stash on Any Error

If a stash was created, it MUST be restored before reporting any error.

This is non-negotiable. Use try-finally logic:

1. If stash was created → remember this
2. Do all operations
3. On ANY failure after stash → restore stash FIRST, then report error
4. On success → restore stash at the end

Workflow

Step 1: Record Initial State and Determine Target Branch

# Save current branch name
CURRENT_BRANCH=$(git branch --show-current)

# Target branch: use user-specified or default to "main"
TARGET_BRANCH="${USER_SPECIFIED_TARGET:-main}"

# Verify target branch exists (locally or on remote)
if ! git show-ref --verify --quiet "refs/heads/$TARGET_BRANCH" && \
   ! git show-ref --verify --quiet "refs/remotes/origin/$TARGET_BRANCH"; then
    echo "ERROR: Target branch '$TARGET_BRANCH' does not exist locally or on remote"
    exit 1
fi

# Verify we're not already on the target branch
if [ "$CURRENT_BRANCH" = "$TARGET_BRANCH" ]; then
    echo "ERROR: Already on target branch '$TARGET_BRANCH'. Cannot rebase onto itself."
    exit 1
fi

Step 2: Stash Changes (if any) — PRESERVING STAGED/UNSTAGED STRUCTURE

Check for uncommitted changes and stash them:

# Check for any changes
HAS_CHANGES=false
if ! git diff --cached --quiet || ! git diff --quiet || [ -n "$(git ls-files --others --exclude-standard)" ]; then
    HAS_CHANGES=true
fi

STASH_CREATED=false
STASH_MSG=""

if [ "$HAS_CHANGES" = true ]; then
    # Stash everything including untracked files, with a unique marker
    STASH_MSG="rebase-skill-auto-stash-$(date +%s)-$$"
    git stash push -u -m "$STASH_MSG"
    STASH_CREATED=true
    echo "Stash created: $STASH_MSG"
fi

Step 3: Fetch and Update Target Branch

From this point on, ANY error must restore the stash first!

# Fetch latest from remote
git fetch origin

# If target branch exists locally, update it
if git show-ref --verify --quiet "refs/heads/$TARGET_BRANCH"; then
    git checkout "$TARGET_BRANCH"
    if ! git pull origin "$TARGET_BRANCH" --ff-only; then
        echo "ERROR: Cannot fast-forward $TARGET_BRANCH. Local branch has diverged."
        # RESTORE STASH BEFORE EXITING
        restore_stash_if_needed
        exit 1
    fi
fi

Step 4: Attempt Rebase

# Return to the original branch
git checkout "$CURRENT_BRANCH"

# Attempt rebase onto target (use origin/target if local doesn't exist)
if git show-ref --verify --quiet "refs/heads/$TARGET_BRANCH"; then
    REBASE_TARGET="$TARGET_BRANCH"
else
    REBASE_TARGET="origin/$TARGET_BRANCH"
fi

if ! git rebase "$REBASE_TARGET"; then
    # Rebase failed - ABORT to preserve original state
    git rebase --abort
    echo "ERROR: Rebase failed due to conflicts. Aborted to preserve original state."
    # RESTORE STASH BEFORE EXITING
    restore_stash_if_needed
    exit 1
fi

echo "Rebase successful!"

Step 5: Push Changes

Only if rebase succeeded:

# Use --force-with-lease for safety (fails if remote has new commits we don't know about)
if ! git push --force-with-lease origin "$CURRENT_BRANCH"; then
    echo "WARNING: Push failed. Someone else may have pushed to this branch."
    echo "Local rebase is intact. You can retry push manually or investigate."
    # Still restore stash - this is a warning, not a fatal error
fi

Step 6: Restore Stashed Changes — WITH STAGED/UNSTAGED PRESERVATION

This step MUST run regardless of success/failure (if stash was created):

restore_stash_if_needed() {
    if [ "$STASH_CREATED" = true ] && [ -n "$STASH_MSG" ]; then
        # Find our stash by its unique message
        STASH_REF=$(git stash list | grep "$STASH_MSG" | head -1 | cut -d: -f1)
        if [ -n "$STASH_REF" ]; then
            # Use --index to PRESERVE the staged/unstaged structure
            if git stash pop --index "$STASH_REF"; then
                echo "Stash restored successfully (staged/unstaged structure preserved)"
            else
                # If --index fails (can happen with conflicts), try without it
                echo "WARNING: Could not restore with staged/unstaged structure."
                echo "Attempting plain restore..."
                git stash pop "$STASH_REF" || {
                    echo "ERROR: Stash restore failed. Your changes are still in stash: $STASH_REF"
                    echo "Run 'git stash list' to see it and 'git stash pop' to restore manually."
                }
            fi
        else
            echo "WARNING: Could not find stash with message: $STASH_MSG"
        fi
    
}


restore_stash_if_needed

Error Handling Summary

Scenario	Action
Target branch doesn't exist	STOP immediately (before stash)
Already on target branch	STOP immediately (before stash)
Detached HEAD	STOP immediately (before stash)
Ongoing rebase/merge	STOP immediately (before stash)
Network unreachable	Restore stash, then STOP
Target branch diverged	Restore stash, then STOP
Rebase conflicts	Abort rebase, restore stash, then STOP
Push rejected	Restore stash, report warning (keep local rebase)
Stash pop conflicts	Report — changes remain in stash for manual recovery

Output Format

Report the following at each stage:

• Current branch: {branch_name}
• Target branch: {target_branch} (user-specified or default)
• Stash created: {yes|no}
• Fetch result: {success|failure}
• Rebase result: {success|aborted due to conflicts}
• Push result: {success|failed|skipped}
• Stash restored: {yes (with index)|yes (without index)|failed|N/A}

Safety Guarantees

1. No data loss — All changes are stashed before any git operations
2. Staged/unstaged preserved — Uses git stash pop --index to maintain staging structure
3. Guaranteed stash restore — Stash is ALWAYS restored on any error after creation
4. Atomic rebase — If rebase fails, it's fully aborted (not left half-done)
5. Safe push — Uses --force-with-lease which fails if remote has unexpected commits
6. Reversible — Original branch state is preserved if anything fails