🚀 [Feature]: Support installing prerelease PowerShell versions

- Update action input description to document prerelease version support
- Fix Windows downgrade detection to handle prerelease version strings
  by stripping the prerelease suffix before casting to [version]
- Fix Windows uninstall registry filter to match Preview display names
  when uninstalling a preview build
- Add prerelease version (7.6.0-preview.6) to test workflow matrix
- Update test verification to detect preview installs on Windows
  (preview builds install to a separate directory)
- Update README with prerelease documentation and usage example

Closes #15

Author: MariusStorhaug

.github/workflows/Action-Test.yml

@@ -22,7 +22,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, windows-latest, macOS-latest]
-        version: ['latest', '7.4.7', '7.5.0']
+        version: ['latest', '7.4.7', '7.5.0', '7.6.0-preview.6']
     runs-on: ${{ matrix.os }}
     name: '${{ matrix.os }} - [${{ matrix.version }}]'
     steps:
@@ -59,8 +59,21 @@ jobs:
               Write-Host "Resolved 'latest' → $requested"
           }
 
-          # Actual version installed by the action
-          $installed = ($PSVersionTable.PSVersion).ToString()
+          # For prerelease versions on Windows, launch the installed pwsh to get the version
+          # because the current shell may not be the version we just installed.
+          $isPrerelease = $requested -match '-'
+          if ($IsWindows -and $isPrerelease) {
+              $majorVersion = ($requested -split '[\.-]')[0]
+              $installDir = "$majorVersion-preview"
+              $pwshPath = "$env:ProgramFiles\PowerShell\$installDir\pwsh.exe"
+              if (Test-Path $pwshPath) {
+                  $installed = (& $pwshPath -NoLogo -NoProfile -Command '$PSVersionTable.PSVersion.ToString()')
+              } else {
+                  $installed = ($PSVersionTable.PSVersion).ToString()
+              }
+          } else {
+              $installed = ($PSVersionTable.PSVersion).ToString()
+          }
           Write-Host "Installed PowerShell version: $installed"
           Write-Host "Expected  PowerShell version: $requested"
 

README.md

@@ -2,6 +2,7 @@
 
 A cross‑platform GitHub Action that installs a specific **PowerShell Core** version—or the latest stable release—on any GitHub‑hosted runner
 (Linux, macOS, or Windows). The action automatically skips installation when the requested version is already present.
+Prerelease versions (e.g. `7.6.0-preview.6`, `7.5.0-rc.1`) are also supported.
 
 ## Usage
 
@@ -25,11 +26,20 @@ jobs:
           Write-Host "Using PowerShell $($PSVersionTable.PSVersion)"
 ```
 
+### Installing a prerelease version
+
+```yaml
+      - name: Install PowerShell Preview
+        uses: PSModule/install-powershell@v1
+        with:
+          Version: 7.6.0-preview.6
+```
+
 ## Inputs
 
 | Input | Required | Default | Description |
 | ----- | -------- | ------- | ----------- |
-| `Version` | `false` | `latest` | Desired PowerShell Core version (e.g. `7.4.1`). Use `latest` to install the newest stable release. |
+| `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. Prerelease versions are supported. |
 
 ## Secrets
 
@@ -43,7 +53,8 @@ This action does **not** generate any outputs.
 
 * **Version resolution**
   If `Version` is set to `latest` (case‑insensitive), the action queries the GitHub API for the newest stable release tag in the
-  `PowerShell/PowerShell` repository and substitutes that version.
+  `PowerShell/PowerShell` repository and substitutes that version. Prerelease version strings (e.g. `7.6.0-preview.6`) are passed
+  through directly.
 
 * **Skip logic**
   Before installing, the action checks the current runner to see whether the requested version is already available

action.yml

@@ -11,8 +11,9 @@ branding:
 inputs:
   Version:
     description: |
-      PowerShell version to install (e.g. `7.4.1`).
+      PowerShell version to install (e.g. `7.4.1` or `7.6.0-preview.6`).
       Defaults to install the latest stable release.
+      Prerelease versions are supported (e.g. `7.6.0-preview.6`, `7.5.0-rc.1`).
     required: false
     default: 'latest'
 
@@ -198,14 +199,20 @@ runs:
         }
 
         # Downgrade detection
+        # Strip prerelease suffix for [version] comparison (e.g. '7.6.0-preview.6' → '7.6.0')
         $isDowngrade = $false
         if ($detected -and $detected -ne $env:REQUESTED_VERSION) {
           try {
-            $detectedVersion  = [version]$detected
-            $requestedVersion = [version]$env:REQUESTED_VERSION
+            $detectedBase  = ($detected -split '-')[0]
+            $requestedBase = ($env:REQUESTED_VERSION -split '-')[0]
+            $detectedVersion  = [version]$detectedBase
+            $requestedVersion = [version]$requestedBase
             if ($detectedVersion -gt $requestedVersion) {
               Write-Host "Downgrade detected: $detected → $($env:REQUESTED_VERSION)"
               $isDowngrade = $true
+            } elseif ($detectedVersion -eq $requestedVersion -and $detected -ne $env:REQUESTED_VERSION) {
+              # Same base version but different prerelease label, treat as a reinstall
+              Write-Host "Version change detected (same base, different label): $detected → $($env:REQUESTED_VERSION)"
             } else {
               Write-Host "Upgrade detected: $detected → $($env:REQUESTED_VERSION)"
             }
@@ -224,13 +231,14 @@ runs:
             'HKLM:\SOFTWARE\WOW6432Node\Microsoft\Windows\CurrentVersion\Uninstall\*'
           )
 
+          $isDetectedPreview = $detected -match '-preview|\-rc'
           $pwshEntries = Get-ItemProperty -Path $regPaths -ErrorAction SilentlyContinue |
             Where-Object {
               $_.Publisher     -eq 'Microsoft Corporation'     -and
               $_.DisplayName   -like 'PowerShell 7*'           -and
-              $_.DisplayName   -notlike '*Preview*'            -and
+              $(if ($isDetectedPreview) { $_.DisplayName -like '*Preview*' } else { $_.DisplayName -notlike '*Preview*' }) -and
               $_.DisplayVersion -and
-              $_.DisplayVersion.StartsWith($detected)
+              $_.DisplayVersion.StartsWith(($detected -split '-')[0])
             }
 
           $targetEntry = $pwshEntries | Select-Object -First 1