How to perform a “totally manual” rebase?

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Summary

Performing a totally manual rebase in Git is a complex process that requires careful consideration of the changes to be applied. The goal is to re-apply changes from a series of commits to a refactored branch without automatic merges or conflict resolution. This process involves starting the rebase process, leaving the working tree intact, and manually implementing changes from each commit.

Root Cause

The root cause of the problem is the need to re-apply changes from a series of commits to a refactored branch, where many of the original changes are no longer relevant. This is due to:

  • Refactored codebase: The feature branch has undergone significant changes, making it difficult to automatically merge or resolve conflicts.
  • Irrelevant changes: Many of the changes in the original commits are no longer applicable to the refactored codebase.
  • Manual intervention required: The need to manually inspect and apply changes from each commit requires a totally manual rebase process.

Why This Happens in Real Systems

This scenario occurs in real systems when:

  • Large-scale refactoring: Significant changes are made to the codebase, making it difficult to integrate new changes.
  • Long-lived feature branches: Feature branches are left open for an extended period, accumulating changes that may no longer be relevant.
  • Complex merge scenarios: Automatic merge tools may struggle to resolve conflicts, requiring manual intervention.

Real-World Impact

The impact of not performing a totally manual rebase in this scenario can be:

  • Lost changes: Relevant changes from the original commits may be lost or overwritten during the rebase process.
  • Incorrect merges: Automatic merge tools may introduce errors or inconsistencies, leading to downstream problems.
  • Increased maintenance: The resulting codebase may require additional maintenance or refactoring to correct errors or inconsistencies.

Example or Code

# Start the rebase process
git rebase -i --onto develop feature-branch

# Leave the working tree intact
git reset --hard HEAD

# Manually implement changes from each commit
git cherry-pick -n 

# Apply manual changes and commit
git add .
git commit -m "Manual rebase of "

How Senior Engineers Fix It

Senior engineers fix this issue by:

  • Carefully planning the rebase process: Identifying the relevant changes and creating a plan for manual application.
  • Using Git tools effectively: Utilizing Git commands, such as git cherry-pick and git rebase, to manage the rebase process.
  • Manually inspecting and applying changes: Carefully reviewing each commit and applying relevant changes to the refactored codebase.

Why Juniors Miss It

Junior engineers may miss this issue due to:

  • Lack of experience with complex merge scenarios: Inadequate understanding of Git tools and merge strategies.
  • Insufficient planning and preparation: Failing to carefully plan and prepare for the rebase process.
  • Overreliance on automatic merge tools: Relying too heavily on automatic merge tools, rather than taking a totally manual approach when necessary.

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