Stage 3: Forward BuildProjectFile* callbacks from OOP TaskHost to worker node

scripts/test-external-repos.ps1

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+<#
+.SYNOPSIS
+    Builds external repos and projects using bootstrap MSBuild to validate callback changes.
+
+.DESCRIPTION
+    Clones dotnet/roslyn to Q:\, creates a WPF test project, then builds them using the
+    locally-built bootstrap MSBuild with TaskHost callbacks enabled and multithreaded mode (-mt).
+    Re-run after rebuilding bootstrap to validate new changes.
+
+    WPF repo itself requires SDK 11.0 so we test with 'dotnet new wpf' instead.
+
+.PARAMETER Repos
+    Which to build. Default: both. Options: 'roslyn', 'wpf', 'both'
+
+.PARAMETER SkipClone
+    Skip cloning if repos already exist at Q:\roslyn and Q:\wpf.
+
+.PARAMETER CleanBuild
+    Delete artifacts/bin before building to force a clean build.
+
+.EXAMPLE
+    # First run: clone + build both
+    .\scripts\test-external-repos.ps1
+
+    # Re-run after rebuilding bootstrap (skip clone, just rebuild)
+    .\scripts\test-external-repos.ps1 -SkipClone
+
+    # Build only roslyn
+    .\scripts\test-external-repos.ps1 -Repos roslyn -SkipClone
+#>
+param(
+    [ValidateSet('roslyn', 'wpf', 'both')]
+    [string]$Repos = 'both',
+
+    [switch]$SkipClone,
+
+    [switch]$CleanBuild
+)
+
+$ErrorActionPreference = 'Continue'
+
+# --- Paths ---
+$msbuildRoot   = "C:\Users\janprovaznik\dev\msbuild"
+$bootstrapRoot = "$msbuildRoot\artifacts\bin\bootstrap"
+$bootstrapDotnet = "$bootstrapRoot\core\dotnet.exe"
+$bootstrapMSBuildExe = "$bootstrapRoot\net472\MSBuild\Current\Bin\MSBuild.exe"
+
+# Find the SDK version in bootstrap
+$sdkDir = Get-ChildItem "$bootstrapRoot\core\sdk" -Directory | Sort-Object Name -Descending | Select-Object -First 1
+$bootstrapSdkPath = $sdkDir.FullName
+
+Write-Host "============================================" -ForegroundColor Cyan
+Write-Host " External Repo Build Validation" -ForegroundColor Cyan
+Write-Host "============================================" -ForegroundColor Cyan
+Write-Host ""
+Write-Host "Bootstrap dotnet : $bootstrapDotnet"
+Write-Host "Bootstrap SDK    : $bootstrapSdkPath"
+Write-Host "Bootstrap MSBuild: $bootstrapMSBuildExe"
+Write-Host ""
+
+# Verify bootstrap exists
+if (-not (Test-Path $bootstrapDotnet)) {
+    Write-Error "Bootstrap dotnet not found at $bootstrapDotnet. Run 'build.cmd' first."
+    exit 1
+}
+
+# --- Environment: enable callbacks + multithreaded ---
+$env:MSBUILDENABLETASKHOSTCALLBACKS = "1"
+$env:DOTNET_ROOT = "$bootstrapRoot\core"
+$env:DOTNET_MSBUILD_SDK_RESOLVER_CLI_DIR = "$bootstrapRoot\core"
+# Use bootstrap dotnet for SDK resolution
+$env:PATH = "$bootstrapRoot\core;$env:PATH"
+
+Write-Host "Environment:" -ForegroundColor Yellow
+Write-Host "  MSBUILDENABLETASKHOSTCALLBACKS = 1"
+Write-Host "  DOTNET_ROOT = $env:DOTNET_ROOT"
+Write-Host ""
+
+# --- Helper: Clone or update repo ---
+function Ensure-Repo {
+    param([string]$Org, [string]$Name, [string]$TargetDir)
+
+    if (Test-Path $TargetDir) {
+        if ($SkipClone) {
+            Write-Host "[$Name] Using existing clone at $TargetDir" -ForegroundColor Green
+            return
+        }
+        Write-Host "[$Name] Removing existing clone..." -ForegroundColor Yellow
+        Remove-Item -Recurse -Force $TargetDir
+    }
+
+    Write-Host "[$Name] Cloning $Org/$Name to $TargetDir (shallow)..." -ForegroundColor Yellow
+    git clone --depth 1 "https://github.com/$Org/$Name.git" $TargetDir
+    if ($LASTEXITCODE -ne 0) {
+        Write-Error "Failed to clone $Org/$Name"
+        return $false
+    }
+    return $true
+}
+
+# --- Helper: Build a repo ---
+function Build-Repo {
+    param(
+        [string]$Name,
+        [string]$RepoDir,
+        [string]$BuildCommand
+    )
+
+    Write-Host ""
+    Write-Host "============================================" -ForegroundColor Cyan
+    Write-Host " Building $Name" -ForegroundColor Cyan
+    Write-Host "============================================" -ForegroundColor Cyan
+
+    Push-Location $RepoDir
+    try {
+        if ($CleanBuild -and (Test-Path "artifacts\bin")) {
+            Write-Host "[$Name] Cleaning artifacts..." -ForegroundColor Yellow
+            Remove-Item -Recurse -Force "artifacts\bin" -ErrorAction SilentlyContinue
+        }
+
+        $logFile = "Q:\${Name}-build.binlog"
+        Write-Host "[$Name] Build command: $BuildCommand" -ForegroundColor Yellow
+        Write-Host "[$Name] Binlog: $logFile" -ForegroundColor Yellow
+        Write-Host ""
+
+        $sw = [System.Diagnostics.Stopwatch]::StartNew()
+        Invoke-Expression $BuildCommand | Out-Host
+        $exitCode = $LASTEXITCODE
+        $sw.Stop()
+
+        if ($exitCode -eq 0) {
+            Write-Host ""
+            Write-Host "[$Name] BUILD SUCCEEDED in $($sw.Elapsed.ToString('mm\:ss'))" -ForegroundColor Green
+        } else {
+            Write-Host ""
+            Write-Host "[$Name] BUILD FAILED (exit code $exitCode) after $($sw.Elapsed.ToString('mm\:ss'))" -ForegroundColor Red
+            Write-Host "[$Name] Check binlog: $logFile" -ForegroundColor Red
+        }
+
+        return $exitCode
+    } finally {
+        Pop-Location
+    }
+}
+
+# --- Ensure Q: exists ---
+if (-not (Test-Path "Q:\")) {
+    Write-Error "Q:\ drive does not exist. Please create or mount it first."
+    exit 1
+}
+
+$results = @{}
+
+# --- Roslyn ---
+if ($Repos -eq 'roslyn' -or $Repos -eq 'both') {
+    $roslynDir = "Q:\roslyn"
+    Ensure-Repo -Org "dotnet" -Name "roslyn" -TargetDir $roslynDir
+
+    if (Test-Path $roslynDir) {
+        # Patch global.json to allow rollForward from our bootstrap SDK
+        $globalJsonPath = "$roslynDir\global.json"
+        $globalJson = Get-Content $globalJsonPath -Raw | ConvertFrom-Json
+        $globalJson.sdk.rollForward = "latestFeature"
+        $globalJson | ConvertTo-Json -Depth 10 | Set-Content $globalJsonPath
+
+        # Build Roslyn Compilers solution filter (smaller, faster than full Roslyn.slnx)
+        # -mt enables multithreaded mode which ejects non-thread-safe tasks to TaskHost.
+        $roslynBuildCmd = "& `"$bootstrapDotnet`" build `"$roslynDir\Compilers.slnf`" -c Debug -mt /bl:`"Q:\roslyn-build.binlog`" -v:m --no-restore"
+
+        # Restore with bootstrap dotnet
+        Write-Host "[roslyn] Restoring Compilers.slnf..." -ForegroundColor Yellow
+        Push-Location $roslynDir
+        & $bootstrapDotnet restore Compilers.slnf -v:m 2>&1 | Select-Object -Last 10
+        $restoreExit = $LASTEXITCODE
+        Pop-Location
+
+        if ($restoreExit -ne 0) {
+            Write-Host "[roslyn] RESTORE FAILED (exit code $restoreExit)" -ForegroundColor Red
+            $results['roslyn'] = $restoreExit
+        } else {
+            $results['roslyn'] = Build-Repo -Name "roslyn" -RepoDir $roslynDir -BuildCommand $roslynBuildCmd
+        }
+    }
+}
+
+# --- WPF (dotnet new wpf) ---
+if ($Repos -eq 'wpf' -or $Repos -eq 'both') {
+    $wpfDir = "Q:\wpf-testproject"
+
+    if (-not (Test-Path $wpfDir) -or -not $SkipClone) {
+        Write-Host "[wpf] Creating new WPF project at $wpfDir..." -ForegroundColor Yellow
+        if (Test-Path $wpfDir) { Remove-Item -Recurse -Force $wpfDir }
+        New-Item -ItemType Directory -Path $wpfDir -Force | Out-Null
+
+        # Use system dotnet for scaffolding — temporarily unset bootstrap env to avoid conflicts
+        $savedDotnetRoot = $env:DOTNET_ROOT
+        $savedResolverDir = $env:DOTNET_MSBUILD_SDK_RESOLVER_CLI_DIR
+        $env:DOTNET_ROOT = $null
+        $env:DOTNET_MSBUILD_SDK_RESOLVER_CLI_DIR = $null
+
+        Push-Location $wpfDir
+        & "C:\Program Files\dotnet\dotnet.exe" new wpf -n WpfTestApp --force 2>&1 | Write-Host
+        Pop-Location
+
+        # Restore bootstrap env
+        $env:DOTNET_ROOT = $savedDotnetRoot
+        $env:DOTNET_MSBUILD_SDK_RESOLVER_CLI_DIR = $savedResolverDir
+    } else {
+        Write-Host "[wpf] Using existing WPF project at $wpfDir" -ForegroundColor Green
+    }
+
+    if (Test-Path "$wpfDir\WpfTestApp") {
+        $wpfBuildCmd = "& `"$bootstrapDotnet`" build `"$wpfDir\WpfTestApp\WpfTestApp.csproj`" -c Debug -mt /bl:`"Q:\wpf-build.binlog`" -v:m"
+
+        $results['wpf'] = Build-Repo -Name "wpf" -RepoDir "$wpfDir\WpfTestApp" -BuildCommand $wpfBuildCmd
+    } else {
+        Write-Host "[wpf] Project creation failed." -ForegroundColor Red
+        $results['wpf'] = 1
+    }
+}
+
+# --- Summary ---
+Write-Host ""
+Write-Host "============================================" -ForegroundColor Cyan
+Write-Host " Summary" -ForegroundColor Cyan
+Write-Host "============================================" -ForegroundColor Cyan
+
+foreach ($repo in $results.Keys) {
+    $code = $results[$repo]
+    $status = if ($code -eq 0) { "PASS" } else { "FAIL ($code)" }
+    $color = if ($code -eq 0) { "Green" } else { "Red" }
+    Write-Host "  $repo : $status" -ForegroundColor $color
+}
+
+Write-Host ""
+Write-Host "Binlogs at Q:\*-build.binlog" -ForegroundColor Yellow
+Write-Host "Re-run with -SkipClone after rebuilding bootstrap." -ForegroundColor Yellow

src/Build.UnitTests/BackEnd/BuildProjectFileAndReportPidTask.cs

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+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Collections;
+using System.Diagnostics;
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+
+namespace Microsoft.Build.UnitTests.BackEnd
+{
+    /// <summary>
+    /// A test task that reports its process ID and optionally calls BuildProjectFile
+    /// on a child project. Used by TaskHost reuse E2E tests to verify that a parent
+    /// task and a nested child task run in the same OOP TaskHost process.
+    /// </summary>
+    public class BuildProjectFileAndReportPidTask : Task
+    {
+        /// <summary>
+        /// Path to the project file to build. If empty, just reports PID without building.
+        /// </summary>
+        public string ProjectFile { get; set; } = string.Empty;
+
+        /// <summary>
+        /// Semicolon-separated list of Property=Value pairs to pass as global properties.
+        /// </summary>
+        public string Properties { get; set; } = string.Empty;
+
+        /// <summary>
+        /// The process ID of the TaskHost running this task.
+        /// </summary>
+        [Output]
+        public int ProcessId { get; set; }
+
+        /// <summary>
+        /// Whether the child build succeeded (only meaningful when ProjectFile is set).
+        /// </summary>
+        [Output]
+        public bool BuildSucceeded { get; set; }
+
+        public override bool Execute()
+        {
+            ProcessId = Process.GetCurrentProcess().Id;
+            Log.LogMessage(MessageImportance.High, $"TASKHOST_PID={ProcessId}");
+
+            if (!string.IsNullOrEmpty(ProjectFile))
+            {
+                Hashtable? globalProperties = null;
+                if (!string.IsNullOrEmpty(Properties))
+                {
+                    globalProperties = new Hashtable();
+                    foreach (string pair in Properties.Split(';'))
+                    {
+                        string[] parts = pair.Split(new[] { '=' }, 2);
+                        if (parts.Length == 2)
+                        {
+                            globalProperties[parts[0].Trim()] = parts[1].Trim();
+                        }
+                    }
+                }
+
+                Hashtable targetOutputs = new();
+                BuildSucceeded = BuildEngine.BuildProjectFile(ProjectFile, null, globalProperties, targetOutputs);
+                Log.LogMessage(MessageImportance.High, $"BuildProjectFile({ProjectFile}) = {BuildSucceeded}");
+            }
+            else
+            {
+                BuildSucceeded = true;
+            }
+
+            return true;
+        }
+    }
+}