feat: Allow to debug XamlIl Compilation

packages/Avalonia/AvaloniaBuildTasks.targets

@@ -88,6 +88,7 @@
       <AvaloniaXamlReferencesTemporaryFilePath Condition="'$(AvaloniaXamlReferencesTemporaryFilePath)' == ''">$(IntermediateOutputPath)/Avalonia/references</AvaloniaXamlReferencesTemporaryFilePath>
       <AvaloniaXamlOriginalCopyFilePath Condition="'$(AvaloniaXamlOriginalCopyFilePath)' == ''">$(IntermediateOutputPath)/Avalonia/original.dll</AvaloniaXamlOriginalCopyFilePath>
       <AvaloniaXamlIlVerifyIl Condition="'$(AvaloniaXamlIlVerifyIl)' == ''">false</AvaloniaXamlIlVerifyIl>
+      <AvaloniaXamlIlDebuggerLaunch Condition="'$(AvaloniaXamlIlDebuggerLaunch)' == ''">false</AvaloniaXamlIlDebuggerLaunch> 
     </PropertyGroup>
     <WriteLinesToFile
       Condition="'$(_AvaloniaForceInternalMSBuild)' != 'true'"
@@ -107,6 +108,7 @@
       DelaySign="$(DelaySign)"
       EnableComInteropPatching="$(_AvaloniaPatchComInterop)"
       SkipXamlCompilation="$(_AvaloniaSkipXamlCompilation)"
+      DebuggerLaunch="$(AvaloniaXamlIlDebuggerLaunch)"
     />
     <Exec
       Condition="'$(_AvaloniaUseExternalMSBuild)' == 'true'"

src/Avalonia.Build.Tasks/CompileAvaloniaXamlTask.cs

@@ -1,9 +1,6 @@
 using System;
-using System.Diagnostics;
 using System.IO;
 using System.Linq;
-using System.Reflection;
-using System.Threading;
 using Microsoft.Build.Framework;
 
 namespace Avalonia.Build.Tasks
@@ -41,7 +38,7 @@ namespace Avalonia.Build.Tasks
                 File.ReadAllLines(ReferencesFilePath).Where(l => !string.IsNullOrWhiteSpace(l)).ToArray(),
                 ProjectDirectory, OutputPath, VerifyIl, outputImportance,
                 (SignAssembly && !DelaySign) ? AssemblyOriginatorKeyFile : null,
-                EnableComInteropPatching, SkipXamlCompilation);
+                EnableComInteropPatching, SkipXamlCompilation, DebuggerLaunch);
             if (!res.Success)
                 return false;
             if (!res.WrittenFile)
@@ -87,5 +84,7 @@ namespace Avalonia.Build.Tasks
 
         public IBuildEngine BuildEngine { get; set; }
         public ITaskHost HostObject { get; set; }
+
+        public bool DebuggerLaunch { get; set; }
     }
 }

src/Avalonia.Build.Tasks/XamlCompilerTaskExecutor.cs

@@ -1,13 +1,10 @@
 using System;
-using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 using System.Reflection;
-using System.Text;
 using Avalonia.Markup.Xaml.XamlIl.CompilerExtensions;
 using Microsoft.Build.Framework;
 using Mono.Cecil;
-using Avalonia.Utilities;
 using Mono.Cecil.Cil;
 using Mono.Cecil.Rocks;
 using XamlX;
@@ -44,16 +41,27 @@ namespace Avalonia.Build.Tasks
             string projectDirectory,
             string output, bool verifyIl, MessageImportance logImportance, string strongNameKey, bool patchCom,
             bool skipXamlCompilation)
+        {
+            return Compile(engine, input, references, projectDirectory, output, verifyIl, logImportance, strongNameKey, patchCom
+                , skipXamlCompilation, 
+                debuggerLaunch:false);
+        }
+
+        internal static CompileResult Compile(IBuildEngine engine, string input, string[] references,
+            string projectDirectory,
+            string output, bool verifyIl, MessageImportance logImportance, string strongNameKey, bool patchCom,
+            bool skipXamlCompilation
+            , bool debuggerLaunch)
         {
             var typeSystem = new CecilTypeSystem(references
                 .Where(r => !r.ToLowerInvariant().EndsWith("avalonia.build.tasks.dll"))
                 .Concat(new[] { input }), input);
-            
+
             var asm = typeSystem.TargetAssemblyDefinition;
 
             if (!skipXamlCompilation)
             {
-                var compileRes = CompileCore(engine, typeSystem, projectDirectory, verifyIl, logImportance);
+                var compileRes = CompileCore(engine, typeSystem, projectDirectory, verifyIl, logImportance, debuggerLaunch);
                 if (compileRes == null && !patchCom)
                     return new CompileResult(true);
                 if (compileRes == false)
@@ -62,7 +70,7 @@ namespace Avalonia.Build.Tasks
 
             if (patchCom)
                 ComInteropHelper.PatchAssembly(asm, typeSystem);
-            
+
             var writerParameters = new WriterParameters { WriteSymbols = asm.MainModule.HasSymbols };
             if (!string.IsNullOrWhiteSpace(strongNameKey))
                 writerParameters.StrongNameKeyBlob = File.ReadAllBytes(strongNameKey);
@@ -70,13 +78,18 @@ namespace Avalonia.Build.Tasks
             asm.Write(output, writerParameters);
 
             return new CompileResult(true, true);
-            
+
         }
-        
+
         static bool? CompileCore(IBuildEngine engine, CecilTypeSystem typeSystem,
             string projectDirectory, bool verifyIl, 
-            MessageImportance logImportance)
+            MessageImportance logImportance
+            , bool debuggerLaunch = false)
         {
+            if (debuggerLaunch)
+            {
+                System.Diagnostics.Debugger.Launch();
+            }
             var asm = typeSystem.TargetAssemblyDefinition;
             var emres = new EmbeddedResources(asm);
             var avares = new AvaloniaResources(asm, projectDirectory);