[Xamarin.Android.Build.Tasks] skip XA1034 logic in some cases (dotnet#7680)

After profiling a build for a `dotnet new maui` app, I noticed:

    193.41ms xamarin.android.build.tasks!Xamarin.Android.Tasks.MonoAndroidHelper.HasResourceDesignerAssemblyReference()

Which equates to:

    Top 10 most expensive tasks
    ...
    AppendCustomMetadataToItemGroup = 204 ms

In dc3ccf2, we added this check to emit `XA1034` when
`$(AndroidUseDesignerAssembly)` is false. And so we don't actually
need to validate this value when it is `true` (the default).

I moved the logic from the `<AppendCustomMetadataToItemGroup/>`
MSBuild task to a new `<CheckForInvalidDesignerConfig/>` task. In most
projects, it will be completely skipped:

    Target "_CheckForInvalidDesignerConfig" skipped, due to false condition; ( '$(AndroidUseDesignerAssembly)' != 'True' ) was evaluated as ( 'true' != 'True' ).

After these changes, I get a much better number in projects with
default settings:

    AppendCustomMetadataToItemGroup = 2 ms

Just by moving the task around, it is faster in general:

    CheckForInvalidDesignerConfig = 11 ms

This is due to less assemblies passed in than before:

    Assemblies="@(_MonoAndroidReferencePath);@(_MonoAndroidReferenceDependencyPaths)"

While previously, we were checking *all* assemblies.

Author: jonathanpeppers

src/Xamarin.Android.Build.Tasks/MSBuild/Xamarin/Android/Xamarin.Android.Resource.Designer.targets

@@ -20,6 +20,7 @@ Copyright (C) 2016 Xamarin. All rights reserved.
 <UsingTask TaskName="Xamarin.Android.Tasks.GenerateResourceDesignerAssembly" AssemblyFile="Xamarin.Android.Build.Tasks.dll" />
 <UsingTask TaskName="Xamarin.Android.Tasks.GenerateResourceCaseMap" AssemblyFile="Xamarin.Android.Build.Tasks.dll" />
 <UsingTask TaskName="Xamarin.Android.Tasks.GenerateRtxt" AssemblyFile="Xamarin.Android.Build.Tasks.dll" />
+<UsingTask TaskName="Xamarin.Android.Tasks.CheckForInvalidDesignerConfig" AssemblyFile="Xamarin.Android.Build.Tasks.dll" />
 
 <PropertyGroup>
   <AndroidUseDesignerAssembly Condition=" '$(AndroidUseDesignerAssembly)' == '' ">False</AndroidUseDesignerAssembly>
@@ -142,15 +143,7 @@ Copyright (C) 2016 Xamarin. All rights reserved.
 <Target Name="_CheckForInvalidDesignerConfig"
     Condition=" '$(AndroidUseDesignerAssembly)' != 'True' "
     DependsOnTargets="_AddAndroidCustomMetaData">
-  <ItemGroup>
-    <_ErrorItems Include="@(_MonoAndroidReferencePath)" Condition=" '%(_MonoAndroidReferencePath.HasResourceDesignerAssemblyReference)' == 'True' "/>
-    <_ErrorItems Include="@(_MonoAndroidReferenceDependencyPaths)"  Condition=" '%(_MonoAndroidReferenceDependencyPaths.HasResourceDesignerAssemblyReference)' == 'True' "/>
-  </ItemGroup>
-  <AndroidError Code="XA1034"
-      ResourceName="XA1034"
-      FormatArguments="%(_ErrorItems.FullPath)"
-      Condition=" '@(_ErrorItems->Count())' != '0' "
-  />
+  <CheckForInvalidDesignerConfig Assemblies="@(_MonoAndroidReferencePath);@(_MonoAndroidReferenceDependencyPaths)" />
 </Target>
 
 <PropertyGroup>

src/Xamarin.Android.Build.Tasks/Tasks/AppendCustomMetadataToItemGroup.cs

@@ -35,11 +35,6 @@ public override bool RunTask ()
 			foreach (var item in Inputs) {
 				var fn = Path.GetFileNameWithoutExtension (item.ItemSpec);
 				output.Add (item);
-				var md = item.GetMetadata ("HasResourceDesignerAssemblyReference");
-				if (string.IsNullOrEmpty (md)) {
-					var b = MonoAndroidHelper.HasResourceDesignerAssemblyReference (item);
-					item.SetMetadata ("HasResourceDesignerAssemblyReference", MonoAndroidHelper.HasResourceDesignerAssemblyReference (item).ToString ());
-				}
 				List<ITaskItem> metaDataList;
 				if (!metaData.TryGetValue (fn, out metaDataList))
 					continue;

src/Xamarin.Android.Build.Tasks/Tasks/CheckForInvalidDesignerConfig.cs

@@ -0,0 +1,56 @@
+using Microsoft.Android.Build.Tasks;
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+using System.Reflection.Metadata;
+using System.Reflection.PortableExecutable;
+using System.IO;
+
+namespace Xamarin.Android.Tasks
+{
+	/// <summary>
+	/// Emits XA1034 is an assembly has a reference to _Microsoft.Android.Resource.Designer.dll
+	/// * NOTE: only called when $(AndroidUseDesignerAssembly) is false
+	/// </summary>
+	public class CheckForInvalidDesignerConfig : AndroidTask
+	{
+		public override string TaskPrefix => "CIRF";
+
+		public ITaskItem[] Assemblies { get; set; }
+
+		public override bool RunTask ()
+		{
+			if (Assemblies == null)
+				return true;
+
+			foreach (var assembly in Assemblies) {
+				if (HasResourceDesignerAssemblyReference (assembly)) {
+					Log.LogCodedError ("XA1034", Properties.Resources.XA1034, assembly);
+				}
+			}
+
+			return !Log.HasLoggedErrors;
+		}
+
+		static bool HasResourceDesignerAssemblyReference (ITaskItem assembly)
+		{
+			if (!File.Exists (assembly.ItemSpec)) {
+				return false;
+			}
+			using var pe = new PEReader (File.OpenRead (assembly.ItemSpec));
+			var reader = pe.GetMetadataReader ();
+			return HasResourceDesignerAssemblyReference (reader);
+		}
+
+		static bool HasResourceDesignerAssemblyReference (MetadataReader reader)
+		{
+			foreach (var handle in reader.AssemblyReferences) {
+				var reference = reader.GetAssemblyReference (handle);
+				var name = reader.GetString (reference.Name);
+				if (string.CompareOrdinal (name, "_Microsoft.Android.Resource.Designer") == 0) {
+					return true;
+				}
+			}
+			return false;
+		}
+	}
+}

src/Xamarin.Android.Build.Tasks/Utilities/MonoAndroidHelper.cs

@@ -325,28 +325,6 @@ public static bool HasMonoAndroidReference (MetadataReader reader)
 			return false;
 		}
 
-		public static bool HasResourceDesignerAssemblyReference (ITaskItem assembly)
-		{
-			if (!File.Exists (assembly.ItemSpec)) {
-				return false;
-			}
-			using var pe = new PEReader (File.OpenRead (assembly.ItemSpec));
-			var reader = pe.GetMetadataReader ();
-			return HasResourceDesignerAssemblyReference (reader);
-		}
-
-		public static bool HasResourceDesignerAssemblyReference (MetadataReader reader)
-		{
-			foreach (var handle in reader.AssemblyReferences) {
-				var reference = reader.GetAssemblyReference (handle);
-				var name = reader.GetString (reference.Name);
-				if (string.CompareOrdinal (name, "_Microsoft.Android.Resource.Designer") == 0) {
-					return true;
-				}
-			}
-			return false;
-		}
-
 		public static bool IsReferenceAssembly (string assembly)
 		{
 			using (var stream = File.OpenRead (assembly))