Presubmit Stack Fix Skill

This skill describes how to use Pigweed's presubmit script in auto mode to automatically run checks, apply fixes, and continue a rebase across a stack of commits (CLs).

Overview

The auto mode in pw_presubmit streamlines the process of fixing presubmit issues across multiple commits. It starts an interactive rebase and runs checks on each commit. If a check fails but has an automatic fix, it applies the fix and amends the commit. If a check fails and cannot be fixed automatically, it stops and allows the user to fix it manually before resuming.

Usage

Prepare for Presubmit

• Ensure the working tree is clean before starting auto mode. If it is not clean, abort and tell the user to clean the working tree before starting.
• Run git rev-parse HEAD to get the current commit hash (referred to as <COMMIT>).
• Message the user to explain what will happen and warn them that it will change their branch (by amending commits).
• Provide the user with the command to fully undo the changes: git rebase --abort; git reset <COMMIT> --hard.
• Example message to the user:

  I am starting an interactive rebase at <COMMIT>. This will run presubmit checks on each commit in your stack. If a check fails but has an automatic fix, it will apply the fix and amend your commit. This will change your branch history.

  If you need to abort and fully restore your branch to its original state, you can run: git rebase --abort; git reset <COMMIT> --hard

Running Presubmit in Auto Mode

To run presubmit in auto mode on a stack of commits, use the following command:

$ ./pw presubmit --mode auto --ui minimal --program full --base <BASE>

Replace <BASE> with the base commit of the stack (e.g., origin/main or a specific commit hash).

Interacting with the Script

• Automatic Fixes: The script automatically applies fixes for checks that support them (e.g., formatting, copyright notice) and amends the current commit.
• Failures: If a check fails and cannot be automatically fixed, the script stops the rebase at the failing commit and saves its state. It outputs a message indicating failure and provide a path to a resume file (e.g., resume.json).

Workflow for Failures

When the script fails on a commit:

1. Identify the failure: Look at the output to see which step failed and why.

2. Fix the issues: Manually fix the issues, if feasible. Stop and ask the user for input before proceeding if you encounter any of the following:

   • Merge conflicts during the rebase that you are unsure how to resolve.
   • Presubmit failures that require significant design changes or user input.
   • The script failing repeatedly on the same commit after manual fixes.
   • Issues that would require changing files unrelated to the current commit to fix.

3. Stage and Amend: You MUST amend the commit with your fixes before resuming. The script requires a clean working tree.

   $ git add <fixed_files>
   $ git commit --amend --no-edit
   

4. Resume: Run the presubmit command again with the --resume flag and the path to the saved state file.

   $ ./pw presubmit --resume /tmp/pw_presubmit_auto_XXXXXX/resume.json
   

   Replace /tmp/pw_presubmit_auto_XXXXXX/resume.json with the path provided in the failure message.