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AI Agent Instructions for PR Metrics

Project Overview

PR Metrics is a cross-platform GitHub Action and Azure DevOps task that analyzes pull request size and test coverage, updating PR titles with indicators (XS, S, M, L, XL, 2XL, etc) and test coverage symbols (✔ or ⚠️).

Architecture

Multi-Platform Abstraction Pattern

The codebase uses a unique dual-platform architecture with dependency injection:

  • Runners: src/task/src/runners/ - Abstracts GitHub Actions vs Azure Pipelines execution
    • runnerInvoker.ts routes to gitHubRunnerInvoker.ts or azurePipelinesRunnerInvoker.ts
    • Detection: process.env.GITHUB_ACTION determines platform
  • Repos: src/task/src/repos/ - Abstracts GitHub vs Azure DevOps repository APIs
    • reposInvoker.ts routes to gitHubReposInvoker.ts or azureReposInvoker.ts
    • Both extend baseReposInvoker.ts, which provides shared API error handling (e.g., mapping 401/403/404 to access-error messages)
    • tokenManager.ts handles workload identity federation as an alternative to Personal Access Tokens
    • Single codebase handles both GitHub and Azure DevOps repositories

Core Components

  • Entry Point: src/task/index.ts - Simple DI container resolution and error handling
  • Main Logic: src/task/src/pullRequestMetrics.ts - Orchestrates the workflow, calling codeMetricsCalculator.updateDetails() and codeMetricsCalculator.updateComments() in parallel via Promise.all()
  • Metrics Engine: src/task/src/metrics/codeMetricsCalculator.ts - Validates conditions, calculates PR metrics, and defines updateDetails() and updateComments()
  • Git Integration: src/task/src/git/gitInvoker.ts - Executes Git commands for diff analysis (numstat-based metrics)
  • Diff Parsing: src/task/src/git/octokitGitDiffParser.ts - Uses the parse-git-diff library to determine, for each file, the first diff hunk start line (a diff line suitable as a comment anchor) for precise comment placement on GitHub PRs

Key Patterns

  • Dependency Injection: Uses tsyringe with @singleton() and @injectable() decorators
  • Interface Abstraction: All major components implement interfaces (e.g., ReposInvokerInterface, RunnerInvokerInterface)
  • Localization: Resource strings in the src/task/Strings/resources.resjson/ folder with runnerInvoker.loc() calls

Development Workflows

Build Commands (from root)

npm run build:debug    # Builds with source maps for debugging
npm run build:release  # Production build with minification
npm run build:package  # Creates dist/ for GitHub Action
npm run lint           # ESLint with autofix (strict TypeScript rules)
npm run test:fast      # Quick test run during development

File Structure Conventions

  • Production: src/task/src/ - Main source code
  • Tests: src/task/tests/ - Mirror source structure for test files
  • Interfaces: Separate .d.ts files for all major interfaces
  • Build Outputs: debug/, release/ (git-ignored), dist/ (committed for GitHub Action)

Critical Git Command

The core functionality relies on: git diff --numstat --ignore-all-space origin/<target>...pull/<pull_request_id>/merge

Code Standards

TypeScript Conventions

  • Strict ESLint: Flat config (eslint.config.mjs) extending strictTypeChecked and stylisticTypeChecked presets with extensive custom rules
  • Explicit Types: @typescript-eslint/explicit-function-return-type enforced
  • Member Ordering: Specific ordering enforced (fields → constructor → methods)
  • ES Modules: Uses .js extensions in imports for Node.js ESM compatibility

Testing Patterns

  • Framework: Mocha + ts-mockito + c8 for coverage + fast-check for property-based testing
  • Pattern: Arrange-Act-Assert structure
  • Coverage: Maintain high coverage rates (critical for edge cases)
  • Test Files: .spec.ts files mirror source structure; .property.spec.ts files contain property-based (fuzz) tests

Error Handling

  • Early return pattern for validation failures
  • Localized error messages via runnerInvoker.loc()
  • Status setting: setStatusFailed(), setStatusSkipped(), setStatusSucceeded()

Integration Points

Environment Variables

PR_METRICS_ACCESS_TOKEN - The only token variable read by the source code. Typically set to ${{ secrets.GITHUB_TOKEN }} in workflows or to an Azure DevOps PAT. Can also be populated automatically by workload identity federation via TokenManager.

External APIs

  • GitHub: Octokit for REST API calls (@octokit/plugin-rest-endpoint-methods)
  • Azure DevOps: azure-devops-node-api for TFS API calls
  • Git: Shell execution via runner abstraction

Configuration Files

  • GitHub Action: action.yml defines inputs/outputs
  • Azure Task: src/task/task.json defines task metadata and inputs
  • Both configs must stay synchronized for input definitions

Development Tips

  • Use npm run test:fast for rapid iteration during development
  • Debug builds include source maps; check debug/ folder
  • Manual testing instructions in src/task/tests/manualTests/Instructions.md
  • Set system.debug: true in pipelines for verbose logging
  • The localization system requires locInitialize() before using loc() calls