PowerShell-master/.github/instructions/build-checkout-prerequisites.instructions.md

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applyTo:
  - .github/**/*.yml
  - .github/**/*.yaml

Build and Checkout Prerequisites for PowerShell CI

This document describes the checkout and build prerequisites used in PowerShell's CI workflows. It is intended for GitHub Copilot sessions working with the build system.

Overview

The PowerShell repository uses a standardized build process across Linux, Windows, and macOS CI workflows. Understanding the checkout configuration and the Sync-PSTags operation is crucial for working with the build system.

Checkout Configuration

Fetch Depth

All CI workflows that build or test PowerShell use fetch-depth: 1000 in the checkout step:

- name: checkout
  uses: actions/checkout@v5
  with:
    fetch-depth: 1000

Why 1000 commits?

• The build system needs access to Git history to determine version information
• Sync-PSTags requires sufficient history to fetch and work with tags
• 1000 commits provides a reasonable balance between clone speed and having enough history for version calculation
• Shallow clones (fetch-depth: 1) would break versioning logic

Exceptions:

• The changes job uses default fetch depth (no explicit fetch-depth) since it only needs to detect file changes
• The analyze job (CodeQL) uses fetch-depth: '0' (full history) for comprehensive security analysis
• Linux packaging uses fetch-depth: 0 to ensure all tags are available for package version metadata

Workflows Using fetch-depth: 1000

• Linux CI (.github/workflows/linux-ci.yml): All build and test jobs
• Windows CI (.github/workflows/windows-ci.yml): All build and test jobs
• macOS CI (.github/workflows/macos-ci.yml): All build and test jobs

Sync-PSTags Operation

What is Sync-PSTags?

Sync-PSTags is a PowerShell function defined in build.psm1 that ensures Git tags from the upstream PowerShell repository are synchronized to the local clone.

Location

• Function Definition: build.psm1 (line 36-76)
• Called From:
  • .github/actions/build/ci/action.yml (Bootstrap step, line 24)
  • tools/ci.psm1 (Invoke-CIInstall function, line 146)

How It Works

Sync-PSTags -AddRemoteIfMissing

The function:

1. Searches for a Git remote pointing to the official PowerShell repository:

   • https://github.com/PowerShell/PowerShell
   • git@github.com:PowerShell/PowerShell

2. If no upstream remote exists and -AddRemoteIfMissing is specified:

   • Adds a remote named upstream pointing to https://github.com/PowerShell/PowerShell.git

3. Fetches all tags from the upstream remote:

   git fetch --tags --quiet upstream
   

4. Sets $script:tagsUpToDate = $true to indicate tags are synchronized

Why Sync-PSTags is Required

Tags are critical for:

• Version Calculation: Get-PSVersion uses git describe --abbrev=0 to find the latest tag
• Build Numbering: CI builds use tag-based versioning for artifacts
• Changelog Generation: Release notes are generated based on tags
• Package Metadata: Package versions are derived from Git tags

Without synchronized tags:

• Version detection would fail or return incorrect versions
• Builds might have inconsistent version numbers
• The build process would error when trying to determine the version

Bootstrap Step in CI Action

The .github/actions/build/ci/action.yml includes this in the Bootstrap step:

- name: Bootstrap
  if: success()
  run: |-
    Write-Verbose -Verbose "Running Bootstrap..."
    Import-Module .\tools\ci.psm1
    Invoke-CIInstall -SkipUser
    Write-Verbose -Verbose "Start Sync-PSTags"
    Sync-PSTags -AddRemoteIfMissing
    Write-Verbose -Verbose "End Sync-PSTags"
  shell: pwsh

Note: Sync-PSTags is called twice:

1. Once by Invoke-CIInstall (in tools/ci.psm1)
2. Explicitly again in the Bootstrap step

This redundancy ensures tags are available even if the first call encounters issues.

Best Practices for Copilot Sessions

When working with the PowerShell CI system:

1. Always use fetch-depth: 1000 or greater when checking out code for build or test operations

2. Understand that Sync-PSTags requires network access to fetch tags from the upstream repository

3. Don't modify the fetch-depth without understanding the impact on version calculation

4. If adding new CI workflows, follow the existing pattern:

   • Use fetch-depth: 1000 for build/test jobs
   • Call Sync-PSTags -AddRemoteIfMissing during bootstrap
   • Ensure the upstream remote is properly configured

5. For local development, developers should:

   • Have the upstream remote configured
   • Run Sync-PSTags -AddRemoteIfMissing before building
   • Or use Start-PSBuild which handles this automatically

Related Files

• .github/actions/build/ci/action.yml - Main CI build action
• .github/workflows/linux-ci.yml - Linux CI workflow
• .github/workflows/windows-ci.yml - Windows CI workflow
• .github/workflows/macos-ci.yml - macOS CI workflow
• build.psm1 - Contains Sync-PSTags function definition
• tools/ci.psm1 - CI-specific build functions that call Sync-PSTags

Summary

The PowerShell CI system depends on:

1. Adequate Git history (fetch-depth: 1000) for version calculation
2. Synchronized Git tags via Sync-PSTags for accurate versioning
3. Upstream remote access to fetch official repository tags

These prerequisites ensure consistent, accurate build versioning across all CI platforms.