[LayoutBindings] LayoutBindings: 'PreserveAttribute' is obsolete warnings

Fixes #7480

* Remove the use of `PreserveAttribute` as we no longer support Xamarin
  Classic in main.
* Add #pragma and code comments to fix certain CS* warnings which are
  emitted by the C# compiler.
* Ignore a bunch of other warnings in the unit test.

Author: dellis1972

src/Xamarin.Android.Build.Tasks/Tasks/GenerateLayoutBindings.BindingGenerator.cs

@@ -30,8 +30,6 @@ public sealed class State
 				// generating code for the partial Activity class
 				public string BindingClassName { get; }
 
-				public bool LinkerPreserveConstructors { get; set; }
-
 				public List<string> ExtraImportNamespaces { get; } = new List <string> ();
 
 				public string AndroidFragmentType { get; }
@@ -155,20 +153,18 @@ protected virtual void WriteOnSetContentViewPartials (State state)
 				WritePartialClassOnSetContentViewPartial_Int (state);
 			}
 
-			public State BeginBindingFile (StreamWriter writer, string layoutResourceId, string classNamespace, string className, string androidFragmentType, bool linkerPreserveConstructors = true)
+			public State BeginBindingFile (StreamWriter writer, string layoutResourceId, string classNamespace, string className, string androidFragmentType)
 			{
-				var state = new State (writer, className, !String.IsNullOrWhiteSpace (classNamespace), androidFragmentType) {
-					LinkerPreserveConstructors = linkerPreserveConstructors
-				};
+				var state = new State (writer, className, !String.IsNullOrWhiteSpace (classNamespace), androidFragmentType);
 				BeginBindingFile (state, layoutResourceId, classNamespace, className);
-				WriteBindingConstructors (state, className, state.LinkerPreserveConstructors);
+				WriteBindingConstructors (state, className);
 				return state;
 			}
 
 			protected abstract void BeginBindingFile (State state, string layoutResourceId, string classNamespace, string className);
 			public abstract void EndBindingFile (State state);
 
-			protected abstract void WriteBindingConstructors (State state, string className, bool linkerPreserve);
+			protected abstract void WriteBindingConstructors (State state, string className);
 			protected abstract void WriteBindingViewProperty (State state, LayoutWidget widget, string resourceNamespace);
 			protected abstract void WriteBindingFragmentProperty (State state, LayoutWidget widget, string resourceNamespace);
 			protected abstract void WriteBindingMixedProperty (State state, LayoutWidget widget, string resourceNamespace);
@@ -287,10 +283,11 @@ protected void WriteBindingPropertyBackingField (State state, LayoutWidget widge
 				WriteResetLocation (state);
 			}
 
-			public void WriteComment (State state, string text)
+			public void WriteComment (State state, params string [] text)
 			{
 				EnsureArgument (state, nameof (state));
-				WriteLineIndent (state, $"{LineCommentString}{text}");
+				foreach (string line in text)
+					WriteLineIndent (state, $"{LineCommentString}{line}");
 			}
 
 			public void WriteComment (State state, ICollection<string> lines)

src/Xamarin.Android.Build.Tasks/Tasks/GenerateLayoutBindings.CSharpBindingGenerator.cs

@@ -157,8 +157,35 @@ void WriteClassClose (State state)
 				WriteLineIndent (state, "}");
 			}
 
+			void WriteDisableWarnings (State state)
+			{
+				state.WriteLine ("#pragma warning disable CS0618");
+				state.WriteLine ("#pragma warning disable CS8981");
+				state.WriteLine ("#pragma warning disable CS1591");
+			}
+
+			void WriteEnableWarnings (State state)
+			{
+				state.WriteLine ("#pragma warning restore CS1591");
+				state.WriteLine ("#pragma warning restore CS8981");
+				state.WriteLine ("#pragma warning restore CS0618");
+			}
+
+			void WriteAutoGeneratedComment (State state)
+			{
+				state.WriteLine (@"//------------------------------------------------------------------------------
+// <auto-generated>
+//     This code was generated by a tool.
+//
+//     Changes to this file may cause incorrect behavior and will be lost if
+//     the code is regenerated.
+// </auto-generated>
+//------------------------------------------------------------------------------");
+			}
+
 			void WriteFilePreamble (State state, string classNamespace)
 			{
+				WriteAutoGeneratedComment (state);
 				WriteUsings (state);
 				state.WriteLine ();
 				WriteNamespaceOpen (state, classNamespace);
@@ -172,13 +199,15 @@ void WriteNamespaceOpen (State state, string classNamespace)
 				state.WriteLine ($"namespace {classNamespace}");
 				state.WriteLine ("{");
 				state.IncreaseIndent ();
+				WriteDisableWarnings (state);
 			}
 
 			void WriteNamespaceClose (State state)
 			{
 				if (!state.IsInNamespace)
 					return;
 
+				WriteEnableWarnings (state);
 				state.DecreaseIndent ();
 				state.WriteLine ("}");
 			}
@@ -200,15 +229,14 @@ void WriteUsing (State state, string ns)
 				state.WriteLine ($"using global::{ns};");
 			}
 
-			protected override void WriteBindingConstructors (State state, string className, bool linkerPreserve)
+			protected override void WriteBindingConstructors (State state, string className)
 			{
-				WriteConstructor (state, className, "Android.App.Activity", linkerPreserve);
-				WriteConstructor (state, className, "Android.Views.View", linkerPreserve);
+				WriteConstructor (state, className, "Android.App.Activity");
+				WriteConstructor (state, className, "Android.Views.View");
 			}
 
-			void WriteConstructor (State state, string className, string clientType, bool linkerPreserve)
+			void WriteConstructor (State state, string className, string clientType)
 			{
-				WritePreserveAtribute (state, linkerPreserve);
 				WriteLineIndent (state, $"public {className} (");
 				state.IncreaseIndent ();
 				WriteLineIndent (state, $"global::{clientType} client,");
@@ -221,14 +249,6 @@ void WriteConstructor (State state, string className, string clientType, bool li
 				state.WriteLine ();
 			}
 
-			void WritePreserveAtribute (State state, bool linkerPreserve)
-			{
-				if (!linkerPreserve)
-					return;
-
-				WriteLineIndent (state, $"[global::Android.Runtime.PreserveAttribute (Conditional=true)]");
-			}
-
 			public override void EndBindingFile (State state)
 			{
 				EnsureArgument (state, nameof (state));

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

@@ -24,6 +24,10 @@ public class GenerateResourceDesignerIntermediateClass : AndroidTask
 
 namespace %NAMESPACE% {
 	#pragma warning disable IDE0002
+	/// <summary>
+	/// Android Resource Designer class.
+	/// Exposes the Android Resource designer assembly into the project Namespace.
+	/// </summary>
 	public partial class Resource : %BASECLASS% {
 	}
 	#pragma warning restore IDE0002

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/CodeBehindTests.cs

@@ -346,6 +346,7 @@ void SuccessfulBuild_AndroidX (TestProjectInfo testInfo, bool many, bool dtb, Lo
 
 			CopyLogs (testInfo, true);
 			Assert.That (success, Is.True, "Build should have succeeded");
+			Assert.IsTrue (StringAssertEx.ContainsText (builder.LastBuildOutput, " 0 Warning(s)"), $"{builder.BuildLogFile} should have no MSBuild warnings.");
 
 			CopyGeneratedFiles (testInfo);
 
@@ -515,7 +516,8 @@ string GetBuildTarget (bool isDTB)
 		string[] GetBuildProperties (LocalBuilder builder, bool manyBuild, bool dtbBuild, bool referenceAndroidX, params string[] extraConstants)
 		{
 			var ret = new List <string> {
-				"AndroidGenerateLayoutBindings=true"
+				"AndroidGenerateLayoutBindings=true",
+				"\"NoWarn=CS0414;CA1416;CA1422;CS1591;XA1005;XA4225\""
 			};
 			if (manyBuild)
 				ret.Add ("ForceParallelBuild=true");

tests/CodeBehind/BuildTests/CodeBehindBuildTests.NET.csproj

@@ -64,6 +64,6 @@
     <ProjectReference Include="..\CommonSampleLibrary\CommonSampleLibrary.NET.csproj" />
   </ItemGroup>
   <ItemGroup Condition=" '$(ReferenceAndroidX)' == 'True' ">
-    <PackageReference Include="Xamarin.AndroidX.AppCompat" Version="1.4.1.1" />
+    <PackageReference Include="Xamarin.AndroidX.AppCompat" Version="1.6.1.5" />
   </ItemGroup>
 </Project>

tests/CodeBehind/BuildTests/Properties/AndroidManifest.xml

@@ -1,6 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <manifest xmlns:android="http://schemas.android.com/apk/res/android" android:versionCode="1" android:versionName="1.0" package="com.xamarin.CodeBehindBuildTests">
-	<uses-sdk android:minSdkVersion="21" />
 	<application android:allowBackup="true" android:icon="@mipmap/icon" android:label="@string/app_name">
 	</application>
 </manifest>