.azure-pipelines: enable Projected File System for unit tests

VFS for Git's runtime and several of its unit tests P/Invoke into
ProjectedFSLib.dll (e.g. Microsoft.Windows.ProjFS.ProjFSNative
.PrjDoesNameContainWildCards via ActiveEnumeration). That DLL is only
present on disk when the 'Client-ProjFS' Windows optional feature is
enabled.

The 1ES win-x86_64-ado1es image used by the new release pipeline does
not have that feature enabled, so RunUnitTests.bat fails with:

    System.DllNotFoundException : Unable to load DLL
    'ProjectedFSLib.dll' or one of its dependencies. (0x8007007E)
       at Microsoft.Windows.ProjFS.ProjFSNative.PrjDoesNameContainWildCards(...)
       at GVFS.Platform.Windows.ActiveEnumeration.SaveFilter(...)
       at GVFS.UnitTests.Windows.Virtualization.ActiveEnumerationTests
          .CannotSetMoreThanOneFilter()

Add a small PowerShell helper that enables the feature, and run it as
a build prereq. The script is a no-op when the feature is already
enabled, so it's safe to keep across image refreshes.

Signed-off-by: Matthew John Cheetham <mjcheetham@outlook.com>

Author: mjcheetham

.azure-pipelines/release.yml

@@ -116,6 +116,11 @@ extends:
                 inputs:
                   filePath: $(Build.SourcesDirectory)\.azure-pipelines\scripts\install-vs-cpp-workload.ps1
 
+              - task: PowerShell@2
+                displayName: 'Enable Projected File System (ProjFS)'
+                inputs:
+                  filePath: $(Build.SourcesDirectory)\.azure-pipelines\scripts\enable-projfs.ps1
+
               - script: |
                   $(Build.SourcesDirectory)\scripts\Build.bat ^
                     $(BuildConfiguration) ^

.azure-pipelines/scripts/enable-projfs.ps1

@@ -0,0 +1,45 @@
+<#
+.SYNOPSIS
+    Enable the Windows Projected File System (ProjFS) optional feature.
+
+.DESCRIPTION
+    VFS for Git -- both the runtime and several unit tests -- P/Invokes
+    into ProjectedFSLib.dll (e.g. PrjDoesNameContainWildCards). That DLL
+    is only present on disk when the 'Client-ProjFS' Windows optional
+    feature is enabled. Hosted CI images do not enable it by default,
+    so unit tests fail with:
+
+        System.DllNotFoundException : Unable to load DLL
+        'ProjectedFSLib.dll' or one of its dependencies.
+
+    This script is a no-op when the feature is already enabled.
+#>
+
+#Requires -Version 5
+#Requires -RunAsAdministrator
+
+[CmdletBinding()]
+param()
+
+$ErrorActionPreference = 'Stop'
+
+$featureName = 'Client-ProjFS'
+
+$feature = Get-WindowsOptionalFeature -Online -FeatureName $featureName -ErrorAction Stop
+if ($feature.State -eq 'Enabled') {
+    Write-Host "INFO: Windows optional feature '$featureName' is already enabled."
+    exit 0
+}
+
+Write-Host "INFO: Enabling Windows optional feature '$featureName'..."
+$result = Enable-WindowsOptionalFeature -Online -FeatureName $featureName -NoRestart -ErrorAction Stop
+
+if ($result.RestartNeeded) {
+    # The pipeline runs unit tests immediately after this script which P/Invoke
+    # into ProjectedFSLib.dll. If the OS reports a reboot is required to make
+    # the feature usable, the build agent is in an inconsistent state and the
+    # tests will fail unpredictably -- so fail fast here instead.
+    throw "Windows optional feature '$featureName' was enabled but a restart is required to take effect; failing the build."
+} else {
+    Write-Host "INFO: Windows optional feature '$featureName' is now enabled."
+}