[Java.Interop] Target .NET Standard 2.0

We would like to be able to build [xamarin-android][0]'s
`Xamarin.Android.sln` within Visual Studio (Windows).

@joj believes that the difficulty is "caused" by
`src/Java.Interop/Java.Interop.csproj` being a PCL project, and thus
if we migrated our PCL projects to instead use .NET Standard the
difficulties would be resolved.

Update `Java.Interop`, `Java.Interop.Dynamic`, `Java.Interop.Export`,
and `Java.Interop.GenericMarshaler` to be .NET Standard 2.0 projects
instead of PCL projects.

This in turn requires updating *every other project* to have a
`$(TargetFrameworkVersion)` value of v4.6.1 (or later) so that they
can reference .NET Standard 2.0 libraries.

Additionally, `make fxcop` and related need to be updated, as the
output paths for .NET Standard 2.0 builds has changed.

Migrating to .NET Standard 2 *also* impacts the downstream
xamarin-android repo: building `xamarin-android/src/Mono.Android`
would fail:

	Microsoft.NuGet.targets(184,5): error : Your project is not referencing the "MonoAndroid,Version=v1.0" framework. Add a reference to "MonoAndroid,Version=v1.0" in the "frameworks" section of your project.json, and then re-run NuGet restore.

The fix for this is twofold:

 1. Provide a new `Java.Interop-MonoAndroid.csproj` file for use by
    the `xamarin-android/src/Mono.Android` build [^1], and

 2. *Override* the `$(BaseIntermediateOutputPath)` MSBuild property.
    `$(BaseIntermediateOutputPath)` is used to find the
    `project*.json` files within `Microsoft.NuGet.targets`, and
    altering `$(BaseIntermediateOutputPath)` thus prevents the
    `project*.json` files from being found, allowing the build to
    succeed.

Finally, building .NET Standard 2 projects often requires that the
`msbuild /restore` or `msbuild /t:Restore` commands be used.
Integrate `msbuild /t:Restore` into `make prepare`, and fix the
`src/java-interop` project so that `msbuild /t:Restore` works without
emitting errors.

[0]: https://github.com/xamarin/xamarin-android/

[^1]: The following patch needs to be applied to `xamarin-android`
      when performing the next `Java.Interop` submodule bump:

diff --git a/src/Mono.Android/Mono.Android.targets b/src/Mono.Android/Mono.Android.targets
index 1d7e0c1a..848a3f63 100644
--- a/src/Mono.Android/Mono.Android.targets
+++ b/src/Mono.Android/Mono.Android.targets
@@ -20,7 +20,7 @@
       </_GlobalProperties>
     </PropertyGroup>
     <MSBuild
-        Projects="$(JavaInteropFullPath)\src\Java.Interop\Java.Interop.csproj"
+        Projects="$(JavaInteropFullPath)\src\Java.Interop\Java.Interop-MonoAndroid.csproj"
         Properties="$(_GlobalProperties)"
     />
     <ItemGroup>

Makefile

@@ -51,14 +51,17 @@ run-all-tests: run-tests run-test-jnimarshal run-test-generator-core run-ptests
 
 include build-tools/scripts/msbuild.mk
 
+prepare:: src/Java.Runtime.Environment/Java.Runtime.Environment.dll.config
+
 prepare:: prepare-bootstrap
+	$(MSBUILD) $(MSBUILD_FLAGS) /t:Restore Java.Interop.sln
 
 prepare-bootstrap: prepare-external bin/Build$(CONFIGURATION)/Java.Interop.BootstrapTasks.dll
 
 bin/Build$(CONFIGURATION)/Java.Interop.BootstrapTasks.dll: build-tools/Java.Interop.BootstrapTasks/Java.Interop.BootstrapTasks.csproj \
 		external/xamarin-android-tools/src/Xamarin.Android.Tools.AndroidSdk/Xamarin.Android.Tools.AndroidSdk.csproj \
 		$(wildcard build-tools/Java.Interop.BootstrapTasks/Java.Interop.BootstrapTasks/*.cs)
-	$(MSBUILD) $(MSBUILD_FLAGS) "$<"
+	$(MSBUILD) $(MSBUILD_FLAGS) /restore "$<"
 
 prepare-external $(PREPARE_EXTERNAL_FILES): $(PACKAGES) $(NUNIT_CONSOLE)
 	git submodule update --init --recursive
@@ -82,15 +85,13 @@ else
 	JAVA_RUNTIME_ENVIRONMENT_DLLMAP_OVERRIDE_CMD = '/@JAVA_RUNTIME_ENVIRONMENT_DLLMAP@/ {' -e 'r $(JAVA_RUNTIME_ENVIRONMENT_DLLMAP_OVERRIDE)' -e 'd' -e '}'
 endif
 
-prepare:: src/Java.Runtime.Environment/Java.Runtime.Environment.dll.config
-
 src/Java.Runtime.Environment/Java.Runtime.Environment.dll.config: src/Java.Runtime.Environment/Java.Runtime.Environment.dll.config.in \
 		bin/Build$(CONFIGURATION)/JdkInfo.props
 	sed -e 's#@JI_JVM_PATH@#$(JI_JVM_PATH)#g' -e 's#@OS_NAME@#$(DLLMAP_OS_NAME)#g' -e $(JAVA_RUNTIME_ENVIRONMENT_DLLMAP_OVERRIDE_CMD) < $< > $@
 
-fxcop: lib/gendarme-2.10/gendarme.exe bin/GendarmeDebug/Java.Interop.dll
-	cp src/Java.Interop/obj/Gendarme/Java.Interop.dll.mdb bin/GendarmeDebug/
-	$(RUNTIME) $< --html gendarme.html $(if @(GENDARME_XML),--xml gendarme.xml) --ignore gendarme-ignore.txt bin/GendarmeDebug/Java.Interop.dll
+fxcop: lib/gendarme-2.10/gendarme.exe bin/GendarmeDebug/netstandard2.0/Java.Interop.dll
+	cp src/Java.Interop/obj/Gendarme/netstandard2.0/Java.Interop.dll.mdb bin/GendarmeDebug/netstandard2.0
+	$(RUNTIME) $< --html gendarme.html $(if @(GENDARME_XML),--xml gendarme.xml) --ignore gendarme-ignore.txt bin/GendarmeDebug/netstandard2.0/Java.Interop.dll
 
 lib/gendarme-2.10/gendarme.exe:
 	-mkdir -p `dirname "$@"`
@@ -127,7 +128,7 @@ bin/Test$(CONFIGURATION)/Android.Interop-Tests.dll: $(wildcard src/Android.Inter
 bin/$(CONFIGURATION)/Java.Interop.dll: $(wildcard src/Java.Interop/*/*.cs) src/Java.Interop/Java.Interop.csproj
 	$(MSBUILD) $(if $(V),/v:diag,) /p:Configuration=$(CONFIGURATION) $(if $(SNK),"/p:AssemblyOriginatorKeyFile=$(SNK)",)
 
-bin/GendarmeDebug/Java.Interop.dll: $(wildcard src/Java.Interop/*/*.cs) src/Java.Interop/Java.Interop.csproj
+bin/GendarmeDebug/netstandard2.0/Java.Interop.dll: $(wildcard src/Java.Interop/*/*.cs) src/Java.Interop/Java.Interop.csproj
 	$(MSBUILD) $(if $(V),/v:diag,) /p:Configuration="Gendarme" $(if $(SNK),"/p:AssemblyOriginatorKeyFile=$(SNK)",) /p:CscToolExe=`which mcs` src/Java.Interop/Java.Interop.csproj
 
 CSHARP_REFS = \

build-tools/Java.Interop.BootstrapTasks/Java.Interop.BootstrapTasks.csproj

@@ -7,7 +7,7 @@
     <OutputType>Library</OutputType>
     <RootNamespace>Java.Interop.BootstrapTasks</RootNamespace>
     <AssemblyName>Java.Interop.BootstrapTasks</AssemblyName>
-    <TargetFrameworkVersion>v4.5.1</TargetFrameworkVersion>
+    <TargetFrameworkVersion>v4.6.1</TargetFrameworkVersion>
     <ProductVersion>8.0.30703</ProductVersion>
     <SchemaVersion>2.0</SchemaVersion>
   </PropertyGroup>

samples/Hello/Hello.csproj

@@ -9,7 +9,7 @@
     <OutputType>Exe</OutputType>
     <RootNamespace>Hello</RootNamespace>
     <AssemblyName>Hello</AssemblyName>
-    <TargetFrameworkVersion>v4.5</TargetFrameworkVersion>
+    <TargetFrameworkVersion>v4.6.1</TargetFrameworkVersion>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
     <DebugSymbols>true</DebugSymbols>

src/Java.Interop.Dynamic/Java.Interop.Dynamic.csproj

@@ -1,54 +1,25 @@
 <?xml version="1.0" encoding="utf-8"?>
-<Project DefaultTargets="Build" ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+<Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
-    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
-    <ProductVersion>8.0.30703</ProductVersion>
-    <SchemaVersion>2.0</SchemaVersion>
+    <TargetFramework>netstandard2.0</TargetFramework>
     <ProjectGuid>{AD4468F8-8883-434B-9D4C-E1801BB3B52A}</ProjectGuid>
-    <ProjectTypeGuids>{786C830F-07A1-408B-BD7F-6EE04809D6DB};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
-    <OutputType>Library</OutputType>
-    <RootNamespace>Java.Interop.Dynamic</RootNamespace>
-    <AssemblyName>Java.Interop.Dynamic</AssemblyName>
-    <TargetFrameworkProfile>Profile78</TargetFrameworkProfile>
-    <TargetFrameworkVersion>v4.5</TargetFrameworkVersion>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <SignAssembly>true</SignAssembly>
     <AssemblyOriginatorKeyFile>..\..\product.snk</AssemblyOriginatorKeyFile>
+    <AssemblyTitle>Java.Interop.Dynamic</AssemblyTitle>
+    <Company>Microsoft Corporation</Company>
+    <Copyright>Microsoft Corporation</Copyright>
+    <AssemblyVersion>0.1.0.0</AssemblyVersion>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
-    <DebugSymbols>true</DebugSymbols>
-    <DebugType>full</DebugType>
-    <Optimize>false</Optimize>
     <OutputPath>..\..\bin\Debug</OutputPath>
-    <DefineConstants>DEBUG;</DefineConstants>
-    <ErrorReport>prompt</ErrorReport>
-    <WarningLevel>4</WarningLevel>
-    <ConsolePause>false</ConsolePause>
-    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
-    <DebugType>full</DebugType>
-    <Optimize>true</Optimize>
     <OutputPath>..\..\bin\Release</OutputPath>
-    <ErrorReport>prompt</ErrorReport>
-    <WarningLevel>4</WarningLevel>
-    <ConsolePause>false</ConsolePause>
-    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
   </PropertyGroup>
   <ItemGroup>
-    <Compile Include="Properties\AssemblyInfo.cs" />
-    <Compile Include="Java.Interop.Dynamic\DynamicJavaClass.cs" />
-    <Compile Include="Java.Interop.Dynamic\DynamicJavaInstance.cs" />
-    <Compile Include="Java.Interop.Dynamic\JavaClassInfo.cs" />
-    <Compile Include="Java.Interop.Dynamic\JavaConstructorInfo.cs" />
-    <Compile Include="Java.Interop.Dynamic\JavaFieldInfo.cs" />
-    <Compile Include="Java.Interop.Dynamic\JavaInstanceProxy.cs" />
-    <Compile Include="Java.Interop.Dynamic\JavaMemberInfo.cs" />
-    <Compile Include="Java.Interop.Dynamic\JavaMethodBase.cs" />
-    <Compile Include="Java.Interop.Dynamic\JavaMethodInfo.cs" />
-    <Compile Include="Java.Interop.Dynamic\JniMetaObject.cs" />
+    <Compile Remove="Tests\**\*.cs" />
   </ItemGroup>
-  <Import Project="$(MSBuildExtensionsPath32)\Microsoft\Portable\$(TargetFrameworkVersion)\Microsoft.Portable.CSharp.targets" />
   <ItemGroup>
     <ProjectReference Include="..\Java.Interop\Java.Interop.csproj">
       <Project>{94BD81F7-B06F-4295-9636-F8A3B6BDC762}</Project>

src/Java.Interop.Dynamic/Tests/Java.Interop.Dynamic-Tests.csproj

@@ -9,7 +9,7 @@
     <OutputType>Library</OutputType>
     <RootNamespace>Java.Interop.DynamicTests</RootNamespace>
     <AssemblyName>Java.Interop.Dynamic-Tests</AssemblyName>
-    <TargetFrameworkVersion>v4.5</TargetFrameworkVersion>
+    <TargetFrameworkVersion>v4.6.1</TargetFrameworkVersion>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
     <DebugSymbols>true</DebugSymbols>

src/Java.Interop.Export/Java.Interop.Export.csproj

@@ -1,44 +1,25 @@
 <?xml version="1.0" encoding="utf-8"?>
-<Project DefaultTargets="Build" ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+<Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
-    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
-    <ProductVersion>8.0.30703</ProductVersion>
-    <SchemaVersion>2.0</SchemaVersion>
+    <TargetFramework>netstandard2.0</TargetFramework>
     <ProjectGuid>{B501D075-6183-4E1D-92C9-F7B5002475B1}</ProjectGuid>
-    <ProjectTypeGuids>{786C830F-07A1-408B-BD7F-6EE04809D6DB};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
-    <OutputType>Library</OutputType>
-    <RootNamespace>Java.Interop</RootNamespace>
-    <AssemblyName>Java.Interop.Export</AssemblyName>
-    <TargetFrameworkProfile>Profile78</TargetFrameworkProfile>
-    <TargetFrameworkVersion>v4.5</TargetFrameworkVersion>
     <SignAssembly>true</SignAssembly>
     <AssemblyOriginatorKeyFile>..\..\product.snk</AssemblyOriginatorKeyFile>
+    <AssemblyTitle>Java.Interop.Export</AssemblyTitle>
+    <Company>Microsoft Corporation</Company>
+    <Copyright>Microsoft Corporation</Copyright>
+    <AssemblyVersion>0.1.0.0</AssemblyVersion>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
-    <DebugSymbols>true</DebugSymbols>
-    <DebugType>full</DebugType>
-    <Optimize>false</Optimize>
     <OutputPath>..\..\bin\Debug</OutputPath>
-    <DefineConstants>DEBUG;</DefineConstants>
-    <ErrorReport>prompt</ErrorReport>
-    <WarningLevel>4</WarningLevel>
-    <ConsolePause>false</ConsolePause>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
-    <DebugType>full</DebugType>
-    <Optimize>true</Optimize>
     <OutputPath>..\..\bin\Release</OutputPath>
-    <ErrorReport>prompt</ErrorReport>
-    <WarningLevel>4</WarningLevel>
-    <ConsolePause>false</ConsolePause>
   </PropertyGroup>
   <ItemGroup>
-    <Compile Include="Properties\AssemblyInfo.cs" />
-    <Compile Include="Java.Interop\JavaCallableAttribute.cs" />
-    <Compile Include="Java.Interop\MarshalMemberBuilder.cs" />
+    <Compile Remove="Tests\**\*.cs" />
+    <Compile Remove="Java.Interop\JniLocationException.cs" />
   </ItemGroup>
-  <Import Project="$(MSBuildExtensionsPath32)\Microsoft\Portable\$(TargetFrameworkVersion)\Microsoft.Portable.CSharp.targets" />
   <ItemGroup>
     <ProjectReference Include="..\Java.Interop\Java.Interop.csproj">
       <Project>{94BD81F7-B06F-4295-9636-F8A3B6BDC762}</Project>

src/Java.Interop.GenericMarshaler/Java.Interop.GenericMarshaler.csproj

@@ -1,50 +1,28 @@
 <?xml version="1.0" encoding="utf-8"?>
-<Project DefaultTargets="Build" ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+<Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
-    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
-    <ProductVersion>8.0.30703</ProductVersion>
-    <SchemaVersion>2.0</SchemaVersion>
+    <TargetFramework>netstandard2.0</TargetFramework>
     <ProjectGuid>{D1243BAB-23CA-4566-A2A3-3ADA2C2DC3AF}</ProjectGuid>
-    <ProjectTypeGuids>{786C830F-07A1-408B-BD7F-6EE04809D6DB};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
-    <OutputType>Library</OutputType>
-    <RootNamespace>Java.Interop.GenericMarshaler</RootNamespace>
-    <AssemblyName>Java.Interop.GenericMarshaler</AssemblyName>
-    <TargetFrameworkVersion>v4.5</TargetFrameworkVersion>
-    <TargetFrameworkProfile>Profile111</TargetFrameworkProfile>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <SignAssembly>true</SignAssembly>
     <AssemblyOriginatorKeyFile>..\..\product.snk</AssemblyOriginatorKeyFile>
+    <AssemblyTitle>Java.Interop.GenericMarshaler</AssemblyTitle>
+    <Company>Microsoft Corporation</Company>
+    <Copyright>Microsoft Corporation</Copyright>
+    <AssemblyVersion>0.1.0.0</AssemblyVersion>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
-    <DebugSymbols>true</DebugSymbols>
-    <DebugType>full</DebugType>
-    <Optimize>false</Optimize>
     <OutputPath>..\..\bin\Debug</OutputPath>
-    <DefineConstants>DEBUG;</DefineConstants>
-    <ErrorReport>prompt</ErrorReport>
-    <WarningLevel>4</WarningLevel>
-    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
-    <Optimize>true</Optimize>
     <OutputPath>..\..\bin\Release</OutputPath>
-    <ErrorReport>prompt</ErrorReport>
-    <WarningLevel>4</WarningLevel>
-    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
   </PropertyGroup>
-  <ItemGroup>
-    <Compile Include="Properties\AssemblyInfo.cs" />
-    <Compile Include="Java.Interop.GenericMarshaler\JniPeerInstanceMethodsExtensions.cs">
-      <DependentUpon>Java.Interop.GenericMarshaler\JniPeerInstanceMethodsExtensions.tt</DependentUpon>
-    </Compile>
-  </ItemGroup>
   <ItemGroup>
     <None Include="Java.Interop.GenericMarshaler\JniPeerInstanceMethodsExtensions.tt">
       <Generator>TextTemplatingFileGenerator</Generator>
       <LastGenOutput>Java.Interop.GenericMarshaler\JniPeerInstanceMethodsExtensions.cs</LastGenOutput>
     </None>
   </ItemGroup>
-  <Import Project="$(MSBuildExtensionsPath32)\Microsoft\Portable\$(TargetFrameworkVersion)\Microsoft.Portable.CSharp.targets" />
   <ItemGroup>
     <ProjectReference Include="..\Java.Interop\Java.Interop.csproj">
       <Project>{94BD81F7-B06F-4295-9636-F8A3B6BDC762}</Project>

src/Java.Interop.Tools.Cecil/Java.Interop.Tools.Cecil.csproj

@@ -9,7 +9,7 @@
     <OutputType>Library</OutputType>
     <RootNamespace>Java.Interop.Tools.Cecil</RootNamespace>
     <AssemblyName>Java.Interop.Tools.Cecil</AssemblyName>
-    <TargetFrameworkVersion>v4.5</TargetFrameworkVersion>
+    <TargetFrameworkVersion>v4.6.1</TargetFrameworkVersion>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
     <DebugSymbols>true</DebugSymbols>

src/Java.Interop.Tools.Diagnostics/Java.Interop.Tools.Diagnostics.csproj

@@ -9,7 +9,7 @@
     <OutputType>Library</OutputType>
     <RootNamespace>Java.Interop.Tools.Diagnostics</RootNamespace>
     <AssemblyName>Java.Interop.Tools.Diagnostics</AssemblyName>
-    <TargetFrameworkVersion>v4.5</TargetFrameworkVersion>
+    <TargetFrameworkVersion>v4.6.1</TargetFrameworkVersion>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
     <DebugSymbols>true</DebugSymbols>

src/Java.Interop.Tools.JavaCallableWrappers/Java.Interop.Tools.JavaCallableWrappers.csproj

@@ -9,7 +9,7 @@
     <OutputType>Library</OutputType>
     <RootNamespace>Java.Interop.Tools.JavaCallableWrappers</RootNamespace>
     <AssemblyName>Java.Interop.Tools.JavaCallableWrappers</AssemblyName>
-    <TargetFrameworkVersion>v4.5</TargetFrameworkVersion>
+    <TargetFrameworkVersion>v4.6.1</TargetFrameworkVersion>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
     <DebugSymbols>true</DebugSymbols>

src/Java.Interop.Tools.JavaCallableWrappers/Test/Java.Interop.Tools.JavaCallableWrappers-Tests.csproj

@@ -9,7 +9,7 @@
     <OutputType>Library</OutputType>
     <RootNamespace>Java.Interop.Tools.JavaCallableWrappersTests</RootNamespace>
     <AssemblyName>Java.Interop.Tools.JavaCallableWrappers-Tests</AssemblyName>
-    <TargetFrameworkVersion>v4.5</TargetFrameworkVersion>
+    <TargetFrameworkVersion>v4.6.1</TargetFrameworkVersion>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
     <DebugSymbols>true</DebugSymbols>

src/Java.Interop/.gitignore

@@ -1 +1,2 @@
 Java.Interop/JniEnvironment.g.cs
+obj-MonoAndroid