🚀 [Feature]: Support installing prerelease PowerShell versions

[MariusStorhaug]

Summary

Add support for installing PowerShell prerelease builds in addition to stable releases, following the same UX pattern
as Install-PSResource -Prerelease.

Design

Inputs

Input	Required	Default	Description
Version	false	latest	Desired PowerShell Core version (e.g. 7.4.1, 7.6.0-preview.6). Use latest to install the newest stable release (or newest prerelease when Prerelease is true).
Prerelease	false	false	Install a prerelease version. When true and Version is latest, resolves to the latest prerelease. Similar to -Prerelease on Install-PSResource.

Usage scenarios

Usage	Version	Prerelease	Result
Latest stable	latest (default)	false (default)	Resolves to latest stable via /releases/latest
Latest prerelease	latest	true	Resolves to latest prerelease via /releases API
Specific stable	7.5.0	—	Installs 7.5.0 directly
Specific prerelease	7.6.0-preview.6	—	Installs 7.6.0-preview.6 directly (no flag needed)

Examples

Install latest stable (default):

- uses: PSModule/install-powershell@v1

Install the latest prerelease:

- uses: PSModule/install-powershell@v1
  with:
    Prerelease: true

Install a specific prerelease version:

- uses: PSModule/install-powershell@v1
  with:
    Version: 7.6.0-preview.6

Details

• PowerShell prereleases follow SemVer: Major.Minor.Patch-Label.N (e.g. 7.6.0-preview.6, 7.5.0-rc.1)
• The GitHub Releases API returns releases sorted by created_at descending, so the first prerelease is the latest
• Download artifact naming is consistent between stable and prerelease (the version string is used as-is in URLs)
• On Windows, preview builds install to $env:ProgramFiles\PowerShell\7-preview\ instead of $env:ProgramFiles\PowerShell\7\
• Windows PowerShell 5.1 (used by the Windows step) lacks [semver] — the downgrade detection strips the prerelease
  suffix before [version] comparison
• The Windows uninstall registry filter must match *Preview* display names when uninstalling a preview build

Acceptance criteria

• New Prerelease boolean input added to action.yml
• latest resolves to the latest prerelease when Prerelease is true
• Specific prerelease version strings (e.g. 7.6.0-preview.6) install correctly without the flag
• Windows downgrade detection handles prerelease version strings
• Windows uninstall filter correctly matches preview display names
• Works on all supported platforms: Linux, macOS, and Windows
• CI test matrix covers both prerelease (latest) and specific prerelease versions
• README documents the new input and provides usage examples

Related

• PR Allow installing Preview versions of PowerShell #13 by agriya khetarpal (@agriyakhetarpal) (community contribution)
• PR 🚀 [Feature]: Support installing prerelease PowerShell versions #16 (implementation)