Add Pull Request management commands

[Copilot]

Module lacked commands for PR automation workflows. Needed ability to list/filter PRs, add comments, and update state for scenarios like closing superseded auto-update PRs.

Changes

Public Commands:

• Get-GitHubPullRequest - List with filters (state, head/base branch, sort) or get by number
• Update-GitHubPullRequest - Modify title, body, state, base branch; supports pipeline input
• New-GitHubPullRequestComment - Add comments via Issues API; supports pipeline input

Class:

• GitHubPullRequest - PR representation with null-safe handling for deleted fork repositories

Implementation:

• Private helpers in src/functions/private/PullRequests/ for each operation
• REST API via Invoke-GitHubAPI for CRUD operations
• Error stream output for not-found resources

Example

# Close older auto-update PRs when a new one is created
Get-GitHubPullRequest -Owner 'PSModule' -Repository 'GoogleFonts' -Head 'PSModule:auto-update-*' -State 'open' |
    Sort-Object UpdatedAt | 
    Select-Object -First ($_.Count - 1) |
    ForEach-Object {
        $_ | New-GitHubPullRequestComment -Body "Superseded by newer Auto-Update PR"
        $_ | Update-GitHubPullRequest -State 'closed'
    }

Full examples in examples/PullRequests/PullRequests.ps1.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Add Pull Request management commands (Get, Set/Update, Comment, Close)</issue_title>
<issue_description>## Summary

The GitHub PowerShell module is currently missing commands for managing pull requests. These are needed for automation scenarios such as listing/filtering PRs, adding comments, and closing superseded PRs.

Missing commands

The following commands (or equivalents) would be valuable additions to the module:

Get-GitHubPullRequest

• List/filter pull requests by state, head branch, base branch, etc.
• Get a specific pull request by number.
• Similar to GET /repos/{owner}/{repo}/pulls and GET /repos/{owner}/{repo}/pulls/{pull_number}.

New-GitHubPullRequestComment

• Add a comment to a pull request (via the issues comments endpoint).
• Similar to POST /repos/{owner}/{repo}/issues/{issue_number}/comments.

Set-GitHubPullRequest / Update-GitHubPullRequest

• Update a pull request's state (e.g., close it), title, body, base branch, etc.
• Similar to PATCH /repos/{owner}/{repo}/pulls/{pull_number}.

Use case

In the PSModule/GoogleFonts repository, an automated workflow updates font data and creates a PR. When a new Auto-Update PR is created, older Auto-Update PRs should be commented on (explaining they are superseded) and then closed. This requires the ability to:

1. List open PRs filtered by head branch or title pattern
2. Add a comment to a PR
3. Close a PR by updating its state

Currently we work around this by using the gh CLI directly, but native PowerShell commands in the GitHub module would be preferred for consistency and better integration with the rest of the module.

Related

• REST API: Pulls
• REST API: Issue Comments
  </issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Add Pull Request management commands (Get, Set/Update, Comment, Close) #546

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