[Mono.Android] Fix generated code build warnings

Directory.Build.props

@@ -68,7 +68,6 @@
 
       This can be opted into locally with $(_AndroidTreatWarningsAsErrors) = true.
     -->
-    <_AllowProjectWarnings Condition=" '$(MSBuildProjectFile)' == 'Mono.Android.csproj' ">true</_AllowProjectWarnings>
     <_AllowProjectWarnings Condition=" '$(MSBuildProjectFile)' == 'Mono.Android.NET-Tests.csproj' ">true</_AllowProjectWarnings>
     <_AllowProjectWarnings Condition=" '$(MSBuildProjectFile)' == 'NativeAOT.csproj' ">true</_AllowProjectWarnings>
     <_AllowProjectWarnings Condition=" '$(MSBuildProjectFile)' == 'TestRunner.Core.NET.csproj' ">true</_AllowProjectWarnings>

build-tools/jnienv-gen/Generator.cs

@@ -60,6 +60,8 @@ static void GenerateFile (TextWriter o)
 			o.WriteLine ("//");
 			o.WriteLine ("// To make changes, edit monodroid/tools/jnienv-gen and rerun");
 			o.WriteLine ();
+			o.WriteLine ("#nullable enable");
+			o.WriteLine ();
 			o.WriteLine ("using System;");
 			o.WriteLine ("using System.Runtime.ExceptionServices;");
 			o.WriteLine ("using System.Runtime.InteropServices;");
@@ -199,7 +201,7 @@ static void GenerateJniEnv (TextWriter o)
 					var copyArray = JNIEnvEntries.Single (e => e.Name.StartsWith ("Get", StringComparison.Ordinal) && e.Name.EndsWith ("ArrayRegion", StringComparison.Ordinal) &&
 							e.Parameters [0].Type.Type == entry.ReturnType.Type);
 					o.Write ("\t\t{2} static {0} {1} (", entry.ReturnType.ManagedType, entry.ApiName, entry.Visibility);
-					o.WriteLine ("{0} array)", copyArray.Parameters [3].Type.ManagedType);
+					o.WriteLine ("{0}? array)", copyArray.Parameters [3].Type.ManagedType);
 					o.WriteLine ("\t\t{");
 					o.WriteLine ("\t\t\tif (array == null)");
 					o.WriteLine ("\t\t\t\treturn IntPtr.Zero;");

build-tools/scripts/JavaCallableWrappers.targets

@@ -2,7 +2,7 @@
 <Project DefaultTargets="Build" ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <Target Name="GenerateJavaCallableWrappers"
       AfterTargets="$(JavaCallableWrapperAfterTargets)"
-      Inputs="$(JavaCallableWrapperAbsAssembly);@(JavaCallableWrapperSource)"
+      Inputs="$(MSBuildThisFileFullPath);$(JavaCallableWrapperAbsAssembly);@(JavaCallableWrapperSource)"
       Outputs="$(OutputPath)mono.android.jar">
     <MakeDir Directories="$(IntermediateOutputPath)jcw;$(IntermediateOutputPath)jcw/bin" />
     <ItemGroup>
@@ -29,7 +29,7 @@
         Overwrite="True"
     />
     <PropertyGroup>
-      <_Target>-source $(JavacSourceVersion) -target $(JavacTargetVersion)</_Target>
+      <_Target>--release $(JavacTargetVersion)</_Target>
       <_D>-d "$(IntermediateOutputPath)jcw/bin"</_D>
       <_AndroidJar>"$(AndroidSdkDirectory)\platforms\android-$(AndroidPlatformId)\android.jar"</_AndroidJar>
       <_MonoAndroidJar>$(OutputPath)mono.android.jar</_MonoAndroidJar>

external/Java.Interop/src/Xamarin.SourceWriter/CodeWriter.cs

@@ -12,6 +12,7 @@ public class CodeWriter : IDisposable
 		int indent;
 		bool need_indent = true;
 		string base_indent;
+		readonly Dictionary<string, int> suppression_depth = new Dictionary<string, int> ();
 
 		public CodeWriter (string filename)
 		{
@@ -31,6 +32,38 @@ public void Write (string value)
 			stream.Write (value);
 		}
 
+		// `#pragma warning restore` ends a suppression however many `disable` directives
+		// preceded it, so a nested `disable`/`restore` pair for the same code would stop
+		// suppressing the enclosing scope early. Track how deep each code is nested and let
+		// only the outermost pair be written.
+		public bool BeginWarningSuppression (string code)
+		{
+			if (code == null)
+				throw new ArgumentNullException (nameof (code));
+
+			suppression_depth.TryGetValue (code, out var depth);
+			suppression_depth [code] = depth + 1;
+
+			return depth == 0;
+		}
+
+		public bool EndWarningSuppression (string code)
+		{
+			if (code == null)
+				throw new ArgumentNullException (nameof (code));
+
+			if (!suppression_depth.TryGetValue (code, out var depth) || depth == 0)
+				throw new InvalidOperationException ($"No warning suppression is open for '{code}'.");
+
+			suppression_depth [code] = depth - 1;
+
+			return depth == 1;
+		}
+
+		public bool IsWarningSuppressed (string code) =>
+			suppression_depth.TryGetValue (code, out var depth) && depth > 0;
+
+
 		public void WriteLine ()
 		{
 			stream.WriteLine ();

external/Java.Interop/src/Xamarin.SourceWriter/Models/EventWriter.cs

@@ -4,10 +4,11 @@
 
 namespace Xamarin.SourceWriter
 {
-	public class EventWriter : ISourceWriter
+	public class EventWriter : ISourceWriter, ISuppressWarnings
 	{
 		Visibility visibility;
 
+		public List<WarningSuppression> SuppressWarnings { get; } = new List<WarningSuppression> ();
 		public string Name { get; set; }
 		public TypeReferenceWriter EventType { get; set; }
 		public List<string> Comments { get; } = new List<string> ();
@@ -54,9 +55,11 @@ public void SetVisibility (string visibility)
 
 		public virtual void Write (CodeWriter writer)
 		{
+			this.WriteSuppressWarningsStart (writer);
 			WriteComments (writer);
 			WriteAttributes (writer);
 			WriteSignature (writer);
+			this.WriteSuppressWarningsEnd (writer);
 		}
 
 		public virtual void WriteComments (CodeWriter writer)

external/Java.Interop/src/Xamarin.SourceWriter/Models/FieldWriter.cs

@@ -4,13 +4,14 @@
 
 namespace Xamarin.SourceWriter
 {
-	public class FieldWriter : ISourceWriter
+	public class FieldWriter : ISourceWriter, ISuppressWarnings
 	{
 		Visibility visibility;
 
 		public string Name { get; set; }
 		public TypeReferenceWriter Type { get; set; }
 		public List<string> Comments { get; } = new List<string> ();
+		public List<WarningSuppression> SuppressWarnings { get; } = new List<WarningSuppression> ();
 		public List<AttributeWriter> Attributes { get; } = new List<AttributeWriter> ();
 		public bool IsPublic { get => visibility.HasFlag (Visibility.Public); set => visibility = value ? Visibility.Public : Visibility.Default; }
 		public bool UseExplicitPrivateKeyword { get; set; }
@@ -47,9 +48,11 @@ public void SetVisibility (string visibility)
 
 		public virtual void Write (CodeWriter writer)
 		{
+			this.WriteSuppressWarningsStart (writer);
 			WriteComments (writer);
 			WriteAttributes (writer);
 			WriteSignature (writer);
+			this.WriteSuppressWarningsEnd (writer);
 		}
 
 		public virtual void WriteComments (CodeWriter writer)
@@ -75,16 +78,17 @@ public virtual void WriteSignature (CodeWriter writer)
 			else if (IsPrivate)
 				writer.Write ("private ");
 
+			// `new` must precede `const`, so write it first for all field kinds.
+			if (IsShadow)
+				writer.Write ("new ");
+
 			if (IsStatic)
 				writer.Write ("static ");
 			if (IsReadonly)
 				writer.Write ("readonly ");
 			if (IsConst)
 				writer.Write ("const ");
 
-			if (IsShadow)
-				writer.Write ("new ");
-
 			WriteType (writer);
 
 			if (Value.HasValue ()) {

external/Java.Interop/src/Xamarin.SourceWriter/Models/MethodWriter.cs

@@ -4,14 +4,15 @@
 
 namespace Xamarin.SourceWriter
 {
-	public class MethodWriter : ISourceWriter, ITakeParameters
+	public class MethodWriter : ISourceWriter, ITakeParameters, ISuppressWarnings
 	{
 		Visibility visibility;
 
 		public string Name { get; set; }
 		public List<MethodParameterWriter> Parameters { get; } = new List<MethodParameterWriter> ();
 		public TypeReferenceWriter ReturnType { get; set; }
 		public List<string> Comments { get; } = new List<string> ();
+		public List<WarningSuppression> SuppressWarnings { get; } = new List<WarningSuppression> ();
 		public List<AttributeWriter> Attributes { get; } = new List<AttributeWriter> ();
 		public bool IsPublic { get => visibility == Visibility.Public; set => visibility = value ? Visibility.Public : Visibility.Default; }
 		public bool UseExplicitPrivateKeyword { get; set; }
@@ -53,9 +54,11 @@ public void SetVisibility (string visibility)
 
 		public virtual void Write (CodeWriter writer)
 		{
+			this.WriteSuppressWarningsStart (writer);
 			WriteComments (writer);
 			WriteAttributes (writer);
 			WriteSignature (writer);
+			this.WriteSuppressWarningsEnd (writer);
 		}
 
 		public virtual void WriteComments (CodeWriter writer)

external/Java.Interop/src/Xamarin.SourceWriter/Models/PropertyWriter.cs

@@ -4,14 +4,15 @@
 
 namespace Xamarin.SourceWriter
 {
-	public class PropertyWriter : ISourceWriter
+	public class PropertyWriter : ISourceWriter, ISuppressWarnings
 	{
 		Visibility visibility;
 
 		public string Name { get; set; }
 		public List<MethodParameterWriter> Parameters { get; } = new List<MethodParameterWriter> ();
 		public TypeReferenceWriter PropertyType { get; set; }
 		public List<string> Comments { get; } = new List<string> ();
+		public List<WarningSuppression> SuppressWarnings { get; } = new List<WarningSuppression> ();
 		public List<AttributeWriter> Attributes { get; } = new List<AttributeWriter> ();
 		public bool IsPublic { get => visibility.HasFlag (Visibility.Public); set => visibility |= Visibility.Public; }
 		public bool UseExplicitPrivateKeyword { get; set; }
@@ -57,9 +58,11 @@ public void SetVisibility (string visibility)
 
 		public virtual void Write (CodeWriter writer)
 		{
+			this.WriteSuppressWarningsStart (writer);
 			WriteComments (writer);
 			WriteAttributes (writer);
 			WriteSignature (writer);
+			this.WriteSuppressWarningsEnd (writer);
 		}
 
 		public virtual void WriteComments (CodeWriter writer)

external/Java.Interop/src/Xamarin.SourceWriter/Models/TypeWriter.cs

@@ -5,7 +5,7 @@
 
 namespace Xamarin.SourceWriter
 {
-	public abstract class TypeWriter : ISourceWriter
+	public abstract class TypeWriter : ISourceWriter, ISuppressWarnings
 	{
 		Visibility visibility;
 		int current_priority = 1;
@@ -24,6 +24,11 @@ public abstract class TypeWriter : ISourceWriter
 		public bool IsProtected { get => visibility.HasFlag (Visibility.Protected); set => visibility = value ? Visibility.Protected : Visibility.Default; }
 		public ObservableCollection<MethodWriter> Methods { get; } = new ObservableCollection<MethodWriter> ();
 		public List<string> Comments { get; } = new List<string> ();
+		public List<WarningSuppression> SuppressWarnings { get; } = new List<WarningSuppression> ();
+
+		// Suppressions that only have to cover the type's declaration -- its base list, for
+		// example -- rather than everything the type contains.
+		public WarningSuppressionScope SignatureSuppressions { get; } = new WarningSuppressionScope ();
 		public List<AttributeWriter> Attributes { get; } = new List<AttributeWriter> ();
 		public ObservableCollection<EventWriter> Events { get; } = new ObservableCollection<EventWriter> ();
 		public ObservableCollection<FieldWriter> Fields { get; } = new ObservableCollection<FieldWriter> ();
@@ -77,11 +82,15 @@ public void SetVisibility (string visibility)
 
 		public virtual void Write (CodeWriter writer)
 		{
+			this.WriteSuppressWarningsStart (writer);
 			WriteComments (writer);
 			WriteAttributes (writer);
+			SignatureSuppressions.WriteSuppressWarningsStart (writer);
 			WriteSignature (writer);
+			SignatureSuppressions.WriteSuppressWarningsEnd (writer);
 			WriteMembers (writer);
 			WriteTypeClose (writer);
+			this.WriteSuppressWarningsEnd (writer);
 		}
 
 		public virtual void WriteComments (CodeWriter writer)

external/Java.Interop/src/Xamarin.SourceWriter/Models/WarningSuppression.cs

@@ -0,0 +1,73 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Xamarin.SourceWriter
+{
+	// A single compiler diagnostic that has to be suppressed around one generated member,
+	// together with the reason it cannot be avoided. Suppressions are deliberately scoped to
+	// the member that needs them so that the same diagnostic elsewhere still breaks the build.
+	public class WarningSuppression
+	{
+		public string Code { get; }
+		public string Reason { get; }
+
+		public WarningSuppression (string code, string reason)
+		{
+			Code = code ?? throw new ArgumentNullException (nameof (code));
+			Reason = reason ?? throw new ArgumentNullException (nameof (reason));
+		}
+	}
+
+	// Implemented by the writers that can emit a member-scoped `#pragma warning disable`.
+	public interface ISuppressWarnings
+	{
+		List<WarningSuppression> SuppressWarnings { get; }
+	}
+
+	// A standalone set of suppressions, for the generated constructs that are written
+	// directly to a `CodeWriter` instead of through a writer that implements
+	// `ISuppressWarnings`.
+	public class WarningSuppressionScope : ISuppressWarnings
+	{
+		public List<WarningSuppression> SuppressWarnings { get; } = new List<WarningSuppression> ();
+	}
+
+	public static class WarningSuppressionExtensions
+	{
+		public static void WriteSuppressWarningsStart (this ISuppressWarnings self, CodeWriter writer)
+		{
+			foreach (var suppression in Ordered (self)) {
+				// The writer tracks how deeply each code is nested, so a member inside an
+				// already-suppressed scope does not emit a redundant pair that would end the
+				// enclosing suppression when it is restored.
+				if (!writer.BeginWarningSuppression (suppression.Code))
+					continue;
+
+				writer.WriteLine ($"// {suppression.Reason}");
+				writer.WriteLine ($"#pragma warning disable {suppression.Code}");
+			}
+		}
+
+		public static void WriteSuppressWarningsEnd (this ISuppressWarnings self, CodeWriter writer)
+		{
+			foreach (var suppression in Ordered (self).Reverse ()) {
+				if (!writer.EndWarningSuppression (suppression.Code))
+					continue;
+
+				writer.WriteLine ($"#pragma warning restore {suppression.Code}");
+			}
+		}
+
+		// The same diagnostic can be reported for more than one reason on a single member,
+		// so each code is emitted once, with the reasons combined.
+		static IList<WarningSuppression> Ordered (ISuppressWarnings self) =>
+			self.SuppressWarnings
+				.GroupBy (s => s.Code)
+				.OrderBy (g => g.Key, StringComparer.Ordinal)
+				.Select (g => g.Count () == 1
+					? g.First ()
+					: new WarningSuppression (g.Key, string.Join (" ", g.Select (s => s.Reason).Distinct ())))
+				.ToList ();
+	}
+}