add better detection for bad symlinks

Author: brettfo

DEVELOPER-GUIDE.md

@@ -6,6 +6,8 @@ If you would like to build `dotnet-interactive` tool and its associated librarie
 
 ## Prerequisites
 
+This repo depends on symbolic links between directories.  By default Windows doesn't support this feature.  To work around this scenario, please run the PowerShell script `<root>/src/ensure-symlinks.ps1` as an administrator.  This usually only needs to be run once.
+
 This project depends on .NET 5.0. Before working on the project, check that the .NET prerequisites have been met:
 
    - [Prerequisites for .NET on Windows](https://docs.microsoft.com/en-us/dotnet/core/install/windows?tabs=net50#dependencies)

eng/build.ps1

@@ -36,6 +36,25 @@ try {
     #     }
     # }
 
+    $repoRoot = Resolve-Path "$PSScriptRoot\.."
+    $symlinkDirectories = @(
+        "$repoRoot\src\dotnet-interactive-vscode\stable\src\common",
+        "$repoRoot\src\dotnet-interactive-vscode\stable\.vscode",
+        "$repoRoot\src\dotnet-interactive-vscode\insiders\src\common",
+        "$repoRoot\src\dotnet-interactive-vscode\insiders\.vscode",
+        "$repoRoot\src\dotnet-interactive-npm\src\common",
+        "$repoRoot\src\dotnet-interactive-npm\.vscode",
+        "$repoRoot\src\Microsoft.DotNet.Interactive.Js\src\common",
+        "$repoRoot\src\Microsoft.DotNet.Interactive.Js\.vscode"
+    )
+
+    foreach ($symlinkDir in $symlinkDirectories) {
+        $candidate = Get-Item $symlinkDir -ErrorAction SilentlyContinue
+        if (($null -eq $candidate) -Or (-Not($candidate.Attributes -match "ReparsePoint"))) {
+            throw "The directory '$symlinkDir' was not a symlink.  Please run the script '$repoRoot\src\ensure-symlinks.ps1' **AS ADMIN**."
+        }
+    }
+
     # invoke regular build/test script
     . (Join-Path $PSScriptRoot "common\build.ps1") -projects "$PSScriptRoot\..\dotnet-interactive.sln" @args
     if ($LASTEXITCODE -ne 0) {

src/dotnet-interactive-vscode/DEVGUIDE.md

@@ -1,6 +1,8 @@
 The organization of this extension is a bit complicated.
 ===
 
+This repo depends on symbolic links between directories.  By default Windows doesn't support this feature.  To work around this scenario, please run the PowerShell script `<root>/src/ensure-symlinks.ps1` as an administrator.  This usually only needs to be run once.
+
 # tl;dr -
 
 0. Requirements: