commentprcasdiff

commentprcasdiff

Automates posting CAS diff comments on PRs when module digest changes are detected.

What it does

This tool runs in GitHub Actions when a PR is created against the fetch-modules branch. It:

1. Identifies which state.json files changed in the PR
2. Compares old and new state to find digest transitions (hash changes)
3. Runs casdiff for each transition to show what changed
4. Posts the output as inline review comments at the line where each new digest appears

How it works

State Analysis

Each module's state.json file is append-only and contains references with their content digests:

{
  "references": [
    {"name": "v1.0.0", "digest": "aaa..."},
    {"name": "v1.1.0", "digest": "bbb..."}
  ]
}

The tool:

• Reads the full JSON from both the base branch (main) and head branch (fetch-modules)
• Identifies newly appended references
• Detects when the digest changes between consecutive references
• For each digest change, runs: casdiff <old_ref> <new_ref> --format=markdown

Comment Posting

Comments are posted as PR review comments on the specific line where the new digest first appears in the diff, similar to manual code review comments.

Example: If digest changes from aaa to bbb at reference v1.1.0, a comment is posted at the line containing "digest": "bbb" in the state.json diff.

Local Testing

To test the command locally:

# Set required environment variables
export PR_NUMBER=1234
export BASE_REF=main
export HEAD_REF=fetch-modules
export GITHUB_TOKEN=<your_token>

# Run the command
go run ./cmd/commentprcasdiff

Note: The command expects to be run from the repository root and requires:

• Git repository with the specified refs
• GitHub CLI (gh) installed and authenticated
• Access to post PR comments via GitHub API

Architecture

• main.go: Entry point, orchestrates the workflow
• module_finder.go: Finds changed state.json files using git diff
• state_analyzer.go: Compares JSON arrays to detect digest transitions
• casdiff_runner.go: Executes casdiff commands in parallel
• comment_poster.go: Posts review comments via GitHub API

Error Handling

• If casdiff fails for a transition, the error is logged but doesn't stop the workflow
• Successful transitions still get commented
• All failures are summarized at the end