[Java.Interop, Java.Base] Fix xamarin-android integration issues (#929)

Context: dotnet/android#6549
Context: 7f1a5ab...bc5bcf4

When attempting to bump xamarin-android from 7f1a5ab to bc5bcf4,
the build failed for a number of reasons, including because bc5bcf4
added a "duplicate" type `Java.Interop.JavaTypeParametersAttribute`,
which caused unit tests to fail:

	error CS0433: The type 'JavaTypeParametersAttribute' exists in both
	'Java.Interop, Version=0.1.0.0, Culture=neutral, PublicKeyToken=84e04ff9cfb79065' and
	'Mono.Android, Version=0.0.0.0, Culture=neutral, PublicKeyToken=84e04ff9cfb79065'.

The plan was to use type forwarders for this type from
`Mono.Android.dll` to `Java.Interop.dll`, but in retrospect this
sounds like a potential "forward-incompatible ABI break" (e56a8c8),
as assemblies built against the newer `Mono.Android.dll` (with type
forwarders) won't be usable on previous Xamarin.Android SDKs.

Make `JavaTypeParametersAttribute` conditional on `NET`, so that it's
only included in .NET 6 builds.  .NET SDK for Android will then use
type forwarders, which won't be an issue as there's no previous .NET
release to be forward compatible with.

Update `tests/generator-Tests` so that `JavaTypeParametersAttribute`
is once again provided for non-`NET` builds.

Additionally, commit 111ebca enabled `$(TreatWarningsAsErrors)`=True,
which had an inadvertent side effect of preventing VS2019 from
building the Java.Interop repo, as warning CS8032 is now an error:

	error CS8032: An instance of analyzer System.Text.Json.SourceGeneration.JsonSourceGenerator cannot be created from
	C:\Program Files\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.0\analyzers\dotnet\cs\System.Text.Json.SourceGeneration.dll :
	Could not load file or assembly 'Microsoft.CodeAnalysis, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'
	or one of its dependencies.
	The system cannot find the file specified.

As it happens, the xamarin-android Windows PR builds are on VS2019,
and thus promptly broke.

Fix this error by adding CS8032 to `$(NoWarn)`, and updating various
`.csproj` files so that the `$(NoWarn)` in `Directory.Build.props`
is used everywhere needed.

Finally, update `Java.Base.targets` so that it looks for
`class-parse.dll` and `generator.dll` from `$(UtilityOutputFullPath)`
*not* `$(ToolOutputFullPath)`.  `class-parse.csproj` and
`generator.csproj` both set `$(OutputPath)` to
`$(UtilityOutputFullPath)`, and the correct path must be used in
order for `Java.Base.targets` to find the required utilities.

Author: jonpryor

Directory.Build.props

@@ -91,6 +91,20 @@
     <_RunJNIEnvGen Condition=" '$(JIBuildingForNetCoreApp)' != 'True' ">$(Runtime) "$(_JNIEnvGenPath)"</_RunJNIEnvGen>
   </PropertyGroup>
 
+  <!--
+    When building on a bot w/ VS2019:
+
+      warning CS8032: An instance of analyzer System.Text.Json.SourceGeneration.JsonSourceGenerator cannot be created from
+
+    however, with `$(TreatWarningsAsErrors)`=True, this becomes an error,
+    meaning we can't build on VS2019.
+
+    Ignore CS8032 so that we can build on VS2019.
+    -->
+  <PropertyGroup>
+    <NoWarn>$(NoWarn);CS8032</NoWarn>
+  </PropertyGroup>
+
   <!-- The net6.0 versions of these are stricter and require overloads not available in .NET Framework, so start with just .NET Framework -->
   <PropertyGroup Condition=" '$(JIBuildingForNetCoreApp)' != 'True' ">
     <AnalysisMode>AllEnabledByDefault</AnalysisMode>

src/Java.Base/Java.Base.csproj

@@ -4,7 +4,7 @@
     <TargetFrameworks>net6.0</TargetFrameworks>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <Nullable>enable</Nullable>
-    <NoWarn>8764</NoWarn>
+    <NoWarn>$(NoWarn);8764</NoWarn>
   </PropertyGroup>
 
   <ItemGroup>

src/Java.Base/Java.Base.targets

@@ -1,7 +1,7 @@
 <Project>
 
   <PropertyGroup>
-    <GeneratorPath>$(ToolOutputFullPath)generator.dll</GeneratorPath>
+    <GeneratorPath>$(UtilityOutputFullPath)generator.dll</GeneratorPath>
   </PropertyGroup>
 
   <Target Name="_GetJavaBaseJmodPath">
@@ -17,7 +17,7 @@
       Outputs="$(IntermediateOutputPath)\mcw\api.xml">
     <MakeDir Directories="$(IntermediateOutputPath)mcw" />
     <PropertyGroup>
-      <_ClassParse>"$(ToolOutputFullPath)class-parse.dll"</_ClassParse>
+      <_ClassParse>"$(UtilityOutputFullPath)class-parse.dll"</_ClassParse>
       <_Input>"$(_JavaBaseJmod)"</_Input>
       <_Output>"-o=$(IntermediateOutputPath)/mcw/api.xml"</_Output>
     </PropertyGroup>

src/Java.Interop/Java.Interop-MonoAndroid.csproj

@@ -11,7 +11,7 @@
     <RootNamespace>Java.Interop</RootNamespace>
     <AssemblyName>Java.Interop</AssemblyName>
     <TargetFrameworkVersion Condition=" '$(TargetFrameworkVersion)' == '' ">v4.5</TargetFrameworkVersion>
-    <NoWarn>1591</NoWarn>
+    <NoWarn>$(NoWarn);1591</NoWarn>
     <SignAssembly>true</SignAssembly>
     <AssemblyOriginatorKeyFile>..\..\product.snk</AssemblyOriginatorKeyFile>
     <LangVersion>8.0</LangVersion>

src/Java.Interop/Java.Interop.csproj

@@ -17,7 +17,7 @@
     <TargetFrameworks>netstandard2.0;net6.0</TargetFrameworks>
   </PropertyGroup>
   <PropertyGroup>
-    <NoWarn>1591</NoWarn>
+    <NoWarn>$(NoWarn);1591</NoWarn>
     <SignAssembly>true</SignAssembly>
     <AssemblyOriginatorKeyFile>..\..\product.snk</AssemblyOriginatorKeyFile>
     <DefineConstants>INTEROP;FEATURE_JNIENVIRONMENT_JI_PINVOKES;FEATURE_JNIOBJECTREFERENCE_INTPTRS;INTERNAL_NULLABLE_ATTRIBUTES;$(JavaInteropDefineConstants)</DefineConstants>

src/Java.Interop/Java.Interop/JavaTypeParametersAttribute.cs

@@ -1,5 +1,7 @@
 using System;
 
+#if NET
+
 namespace Java.Interop
 {
 	[AttributeUsage (AttributeTargets.Class | AttributeTargets.Interface | AttributeTargets.Method,
@@ -14,3 +16,5 @@ public JavaTypeParametersAttribute (string [] typeParameters)
 		public string [] TypeParameters { get; }
 	}
 }
+
+#endif  // NET

tests/generator-Tests/Integration-Tests/Compiler.cs

@@ -40,6 +40,9 @@ public static Assembly Compile (Xamarin.Android.Binder.CodeGeneratorOptions opti
 			if (options.CodeGenerationTarget == CodeGenerationTarget.JavaInterop1) {
 				preprocessorSymbols.Add ("JAVA_INTEROP1");
 			}
+#if NET
+			preprocessorSymbols.Add ("NET");
+#endif  // NET
 
 			var parseOptions = new CSharpParseOptions (preprocessorSymbols:preprocessorSymbols);
 

tests/generator-Tests/SupportFiles/JavaTypeParametersAttribute.cs

@@ -0,0 +1,18 @@
+#if !NET
+
+using System;
+
+namespace Java.Interop
+{
+	public class JavaTypeParametersAttribute : Attribute
+	{
+		public JavaTypeParametersAttribute (string [] typeParameters)
+		{
+			TypeParameters = typeParameters;
+		}
+
+		public string [] TypeParameters { get; set; }
+	}
+}
+
+#endif  // !NET