Experimental Code Coverage Verification Prep

Prep Verification Build

This skill modifies workspace files to ensure LUCI builders run, isolates target test suites in builder Starlark files for speed, and uploads a Work-In-Progress (WIP) Gerrit CL. It is used to prepare both experimental branches with fixes and clean baseline branches.

When to Use This Skill

• After making potential configuration fixes and needing to run a verification build.
• To create a "Baseline" CL on a clean branch, with only the necessary modifications to trigger and speed up the build.

Inputs (Read from scratch/triage_state.json)

This skill reads its primary inputs directly from scratch/triage_state.json. The only dynamic selector passed in the subagent prompt is role ("Control" vs. "Fix"):

• target_files: A list of file paths that need a dummy comment to ensure they are included in the build's affected files.
• builders_of_concern: A list of target builder names (e.g. ["linux-rel"]). To locate the .star Starlark configuration file for each builder, reference builder_star_map.json.
• test_suites: The test suite names to isolate in the builder configurations.
• bug_id: The issue ID for context in the CL description.
• control_branch_name / fix_branch_name: The git branch to check out. If role is "Control" (or "control"), check out control_branch_name. If role is "Fix" (or "fix"), check out fix_branch_name.

Workflow

1. Checkout Branch:

   Read scratch/triage_state.json and check out control_branch_name (if role is "Control") or fix_branch_name (if role is "Fix").

   git checkout {{selected_branch_name}}

2. Add Dummy Comments:

   • Iterate through each file in target_files (from scratch/triage_state.json).
   • Append a unique dummy comment to each file (e.g., // Verification run for b/{{bug_id}}).

   # Example for one file
   echo "// Verification run for b/{{bug_id}} $(date)" >> {{file_path}}

3. Optimize Builder Configurations:

   • For each builder in builders_of_concern and its .star file:
     • Locate the builder definition.
     • Modify the test suite declarations to only include the target suites from test_suites (from scratch/triage_state.json).
     • Example Modification: Change existing test bundles to:

       # Example for a builder's test targets
       targets = targets.bundle(targets = {{test_suites}})

     • After modifying the .star file(s), regenerate configuration artifacts directly from the repository root:

       lucicfg generate infra/config/main.star

       This updates the underlying JSON build specifications.

4. Commit Changes:

   • Stage all modified tracked files in the workspace using git add -u. This stages the dummy comments and updated builder configurations while safely ignoring any untracked scratch files or local skills.

   git add -u

   • Create a commit using the structured naming format. Note that the commit title must explicitly state (Control) or (Fix) based on role. If test_suites contains multiple test suites, join their names or list them.
   • Commit Message:

     Verify Code Coverage Change for {{test_suites}} ({{role}})
     
     This was generated by the Code Coverage Debugging Agent.
     
     Role: {{role}} Verification
     Target Files: {{ target_files }}
     
     {{ summary of applied GN/Starlark/recipe fixes or trimming }}
     
     Bug: {{bug_id}}

   git commit \
     -m "Verify Code Coverage Change for {{test_suites}} ({{role}})" \
     -m "This was generated by the Code Coverage Debugging Agent." \
     -m "Role: {{role}} Verification" \
     -m "Target Files: {{ target_files }}" \
     -m "{{ summary of applied GN/Starlark/recipe fixes or trimming }}" \
     -m "Bug: {{bug_id}}"

5. Upload to Gerrit:

   • Upload the CL as a Work-In-Progress (WIP).
   • Do NOT pass --cq-dry-run to the upload command.

   git cl upload -f --bypass-hooks -o wip

6. Update State File:

   • Update scratch/triage_state.json: write the uploaded CL URL into control_cl (if role is "Control") or fix_cl (if role is "Fix").