Detect LongPath enabled on Windows (#1168)

init.ps1

@@ -6,6 +6,13 @@ function ExecSafe([scriptblock] $cmd) {
 Set-StrictMode -Version 2.0; $ErrorActionPreference = "Stop"; $ConfirmPreference = "None"; trap { Write-Error $_ -ErrorAction Continue; exit 1 }
 $PSScriptRoot = Split-Path $MyInvocation.MyCommand.Path -Parent
 
+# Verify LongPath is enabled
+# Forked from https://github.com/dotnet/roslyn/blob/c8eecdb9563127988b3cb564a493eae9ef254a88/eng/build.ps1#L607
+$regKeyProperty = Get-ItemProperty -Path HKLM:\SYSTEM\CurrentControlSet\Control\FileSystem -Name "LongPathsEnabled" -ErrorAction Ignore
+if (($null -eq $regKeyProperty) -or ($regKeyProperty.LongPathsEnabled -ne 1)) {
+  Write-Host -ForegroundColor Yellow "Warning: LongPath is not enabled, you may experience build errors. You can avoid these by enabling LongPath. You can enable it by running `"tools/enable-long-paths.reg`". More information on https://learn.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation?tabs=powershell#enable-long-paths-in-windows-10-version-1607-and-later"
+}
+
 # Install .NET
 ExecSafe { & $PSScriptRoot\tools\Install-DotNet.ps1 -RootFolder $PSScriptRoot }
 

src/Directory.Build.targets

@@ -1,4 +1,15 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project ToolsVersion="4.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <Target Name="_DevToysLongPathEnabled"
+      BeforeTargets="CoreCompile"
+      Condition="'$([MSBuild]::IsOsPlatform(Windows))' and '$(MSBuildThisFileDirectory.Length)' &gt; 25">
+    <!---
+      Validation for LongPath support (source https://github.com/dotnet/roslyn/blob/c8eecdb9563127988b3cb564a493eae9ef254a88/eng/build.ps1#L607)
+      https://docs.microsoft.com/en-us/archive/blogs/jeremykuhne/net-4-6-2-and-long-paths-on-windows-10#enabling-win32-long-path-support
+    -->
 
+    <Warning
+      Condition="'$(registry:HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\FileSystem@LongPathsEnabled)'!='1'"
+      Text="LongPath is not enabled, you may experience build errors. You can avoid these by enabling LongPath. You can enable it by running `tools/enable-long-paths.reg`. More information on https://learn.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation?tabs=powershell#enable-long-paths-in-windows-10-version-1607-and-later"/>
+  </Target>
 </Project>

tools/enable-long-paths.reg

@@ -0,0 +1,4 @@
+Windows Registry Editor Version 5.00
+
+[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\FileSystem]
+"LongPathsEnabled"=dword:00000001