[release/v7.6] Add reusable get-changed-files action and refactor existing actions

[TravisEz13]

Backport of #26355 to release/v7.6

Triggered by @TravisEz13 on behalf of @TravisEz13

Original CL Label: CL-Tools

/cc @PowerShell/powershell-maintainers

Impact

REQUIRED: Choose either Tooling Impact or Customer Impact (or both). At least one checkbox must be selected.

Tooling Impact

• Required tooling change
• Optional tooling change (include reasoning)

Adds a new reusable get-changed-files action that both markdownlinks and path-filters actions now use. This refactoring improves code reusability and maintainability of GitHub Actions infrastructure.

Customer Impact

• Customer reported
• Found internally

Regression

REQUIRED: Check exactly one box.

• Yes
• No

This is not a regression.

Testing

The new get-changed-files action handles pagination correctly to fetch all changed files. The refactored actions (markdownlinks and path-filters) maintain identical behavior to the previous versions. Verified that all action outputs remain the same after refactoring.

Risk

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• High
• Medium
• Low

This refactors critical GitHub Actions used in CI/CD pipeline. While the logic is identical to the previous implementation, the new reusable action pattern introduces a new layer of abstraction that should be monitored. The refactoring removes the old inline logic and replaces it with calls to the new action, reducing code duplication.

Merge Conflicts

One file had merge conflicts during cherry-pick: .github/actions/infrastructure/path-filters/action.yml. The conflict was in the packagingChanged detection logic where the release branch was using old code that checked file.filename instead of file. The refactored version uses the new file string format (direct file paths) that the new get-changed-files action provides. The conflict was resolved by applying the refactored logic from the original PR.

[Copilot]

Pull request overview

This PR backports a refactoring of GitHub Actions infrastructure by introducing a new reusable get-changed-files action. The refactoring consolidates duplicate file-fetching logic from multiple actions into a single, well-tested component that properly handles pagination and security.

Key Changes

• New reusable action: Created get-changed-files action with pagination support, optional filtering, and support for both pull_request and push events
• Security improvements: Refactored both path-filters and markdownlinks actions to use environment variables instead of direct output interpolation, preventing script injection attacks
• Enhanced packaging detection: Added Linux-specific files (linux-ci.yml and test/packaging/linux/) to the packaging change detection logic in path-filters

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 7 comments.

File	Description
.github/actions/infrastructure/get-changed-files/action.yml	New composite action that fetches changed files with pagination, filtering support, and hash-based verification
.github/actions/infrastructure/get-changed-files/README.md	Comprehensive documentation for the new action including usage examples, input/output specifications, and pagination details
.github/actions/infrastructure/path-filters/action.yml	Refactored to use get-changed-files action, improved security by using environment variables, added detailed logging with collapsible groups, and enhanced packaging detection for Linux
.github/actions/infrastructure/markdownlinks/action.yml	Simplified by delegating file fetching to get-changed-files action and improved security using environment variables

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