feat: Add automatic standard CI variable resolution

[aaronsteers]

feat: Add automatic standard CI variable resolution

Summary

This PR implements automatic resolution of standard CI variables from GitHub context, eliminating the need for complex expressions like ${{ github.event.pull_request.head.repo.full_name || github.repository }} throughout workflows.

Key Changes:

• Added standard_ci_vars input parameter (default: false) to enable the feature
• Implements resolution for 20+ standard variables: pr-number, head-ref, base-ref, repo, head-repo, base-repo, etc.
• Smart gitref resolution handles "run from main, operate on PR branch" pattern for slash commands
• Fork-aware: repo variables point to base repository, gitref points to fork's branch
• Issue-aware: Git refs are null for issue events since issues don't have branches
• Maintains full backward compatibility with existing functionality

Review & Testing Checklist for Human

• Test with actual fork PRs - Verify repo resolves to base repo while gitref resolves to fork's branch name
• Test slash commands from different contexts - Verify workflow_dispatch with/without pr input resolves variables correctly
• Test issue vs PR trigger scenarios - Confirm git refs are null for issue events but populated for PR events
• Verify backward compatibility - Run existing workflows with standard_ci_vars: false to ensure no regressions
• Test edge cases - Missing PR data, gh CLI unavailable, workflow_dispatch without clear context

Recommended Test Plan:

1. Create a fork PR and trigger workflows to verify repo vs gitref resolution
2. Test slash commands (/test, etc.) to ensure smart gitref fetches correct branch
3. Run action on issue comments to verify git refs are properly nulled
4. Test with existing workflows to confirm no breaking changes

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Diagram

%%{ init : { "theme" : "default" }}%%
graph TD
    A["action.yml"]:::major-edit --> B["resolve-standard-ci-vars step"]:::major-edit
    A --> C["merge-results step"]:::minor-edit
    D["README.md"]:::major-edit --> E["Standard CI Variables table"]:::major-edit
    F[".github/workflows/test-action.yml"]:::major-edit --> G["test-standard-ci-vars job"]:::major-edit
    
    B --> H["GitHub Context<br/>(github.event.*)"]:::context
    B --> I["Smart gitref resolution<br/>(gh pr view)"]:::context
    C --> J["Final JSON output<br/>(all variables)"]:::context
    
    subgraph Legend
        L1[Major Edit]:::major-edit
        L2[Minor Edit]:::minor-edit  
        L3[Context/No Edit]:::context
    end

    classDef major-edit fill:#90EE90
    classDef minor-edit fill:#87CEEB
    classDef context fill:#FFFFFF

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Notes

• The smart gitref resolution using gh pr view has fallback logic but may need testing in constrained CI environments
• Fork handling logic is critical - ensure repo (base) vs gitref (head) distinction works correctly
• Requested by AJ Steers (@aaronsteers)
• Session: https://app.devin.ai/sessions/2ea6e9db29ce437d8ca81c377c8660b8
• Link to Devin run: https://app.devin.ai/sessions/2ea6e9db29ce437d8ca81c377c8660b8

[devin-ai-integration]

Original prompt from AJ Steers

Received message in Slack channel #dev-ci:

@Devin - Create a PR to the aaronsteers/resolve-vars-action repo. We want to automatically (without requiring custom user input) resolve all/most of the variables we normally have to coalesce from different trigger types like pull request, pull request target, workflow dispatch, etc.. E.g. pr-number, issue-number, head-ref, base-ref, head-repo, base-repo, etc. Plan is to migrate our workflows (eventually) to use this action and make everything cleaner with less code.

[devin-ai-integration]

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[Copilot]

Pull Request Overview

This PR implements automatic resolution of standard CI variables from GitHub context, eliminating the need for complex expressions like ${{ github.event.pull_request.head.repo.full_name || github.repository }} throughout workflows.

• Adds 20+ standard CI variables including pr-number, head-ref, base-ref, repo, and gitref resolution
• Implements smart gitref resolution with fork-aware handling and issue context awareness
• Adds comprehensive test coverage for the new standard CI variables functionality

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
action.yml	Adds new CI variable resolution step with 20+ output variables and smart context detection logic
README.md	Documents the new standard CI variables with comprehensive reference table and usage examples
.github/workflows/test-action.yml	Updates existing tests to use new output format and adds dedicated test job for standard CI variables

Comments suppressed due to low confidence (1)

action.yml:271

• The fallback logic || github.sha will always evaluate to github.sha when github.event.pull_request.head.sha is empty, but GitHub Actions expressions don't work this way. Use proper conditional logic or separate if statements to handle empty values.

          CI_VARS["resolved-git-sha"]="${{ github.sha }}"

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