[build] Support building with JetBrains OpenJDK 11 (#629)

Context: https://issuetracker.google.com/issues/150189789
Context: dotnet/android#4562
Context: dotnet/android#4567

Bumps to xamarin/xamarin-android-tools/master@36d7fee5

Changes: dotnet/android-tools@bfb66f3...36d7fee

  * dotnet/android-tools@36d7fee: JetBrains OpenJDK 11 detection (#82)
  * dotnet/android-tools@12f52ac: Merge pull request #80 from jonpryor/jonp-drop-net461
  * dotnet/android-tools@c7090d0: [Xamarin.Android.Tools.AndroidSdk] Remove net461

JDK 9 -- released 2017-July-27 -- introduced many new features, but
broke various Android SDK toolchain programs in various inscrutable
ways, so the Android community has been "stuck" on JDK 8 ever since.

…until now?  A preview version of `apksigner` in the Build-tools 30rc1
package states that it requires Java 9 in order to run, which means we
must explore what is required to build under JDK > 8.

[JetBrains has an OpenJDK 11.0.4 release for macOS][0], which has a
"weird" directory structure but is otherwise workable, so…

Will It Build™?

	$ curl -o jbrsdk-11_0_4-osx-x64-b546.1.tar.gz https://bintray.com/jetbrains/intellij-jdk/download_file?file_path=jbrsdk-11_0_4-osx-x64-b546.1.tar.gz
	# Above doesn't *actually* work; use a browser to appease Akamai
	$ tar xzf jbrsdk-11_0_4-osx-x64-b546.1.tar.gz
	$ export JAVA_HOME=`pwd`/jbrsdk/Contents/Home
	$ make prepare JI_MAX_JDK=12
	$ make all

Yes, it builds, but that's *misleading*: it's not actually using
`$JAVA_HOME`!

	…/Java.Interop/build-tools/scripts/jdk.targets(5,5): warning : Not a valid JDK directory: `…/Java.Interop/jbrsdk/Contents/Home`; via locator: $JAVA_HOME
	System.ArgumentException: Could not find required file `jvm` within `…/Java.Interop/jbrsdk/Contents/Home`; is this a valid JDK?
	Parameter name: homePath
	  at Xamarin.Android.Tools.JdkInfo.ValidateFile (System.String name, System.String path)
	  at Xamarin.Android.Tools.JdkInfo..ctor (System.String homePath)

This is fixed via dotnet/android-tools@36d7fee.  Bump
xamarin-android-tools, and `make prepare` still works.

`make all` fails:

	$ make all
	…
	  "…/Java.Interop/jbrsdk/Contents/Home/bin/javac" -parameters -source 1.6 -target 1.6 -bootclasspath "…/Java.Interop/jbrsdk/Contents/Home/bin/../jre/lib/rt.jar" -g -d "obj/Debug/classes" java/android/annotation/NonNull.java java/android/annotation/NonNull.java java/com/xamarin/IJavaInterface.java java/com/xamarin/IParameterInterface.java java/com/xamarin/JavaAnnotation.java java/com/xamarin/JavaType.java java/com/xamarin/NestedInterface.java java/com/xamarin/NotNullClass.java java/com/xamarin/ParameterAbstractClass.java java/com/xamarin/ParameterClass.java java/com/xamarin/ParameterClass2.java java/java/util/Collection.java java/NonGenericGlobalType.java
	EXEC : warning : [options] source value 6 is obsolete and will be removed in a future release
	EXEC : warning : [options] target value 1.6 is obsolete and will be removed in a future release
	EXEC : warning : -parameters is not supported for target value 1.6. Use 1.8 or later.
	EXEC : warning : [options] To suppress warnings about obsolete options, use -Xlint:-options.
	  4 warnings
	EXEC : Fatal error : Unable to find package java.lang in classpath or bootclasspath

The problem is that JetBrains' OpenJDK 11 no longer contains a
`…/jre/lib/rt.jar` file, so the `-bootclasspath` value is now wrong.

Additionally, if you don't use `javac -target`, which implicitly
targets JDK 11, `javac` doesn't like that:

	EXEC : error : option --boot-class-path not allowed with target 11

The solution?  Don't Do That™; if `javac` from OpenJDK 11 doesn't want
`-bootclasspath`, don't provide it.

Update the `<JdkInfo/>` task to check for the existence of the
`…/jre/lib/rt.jar` file; if it exists, set `$(JreRtJarPath)`,
otherwise the `$(JreRtJarPath)` MSBuild property is empty.

Then update `$(_JavacSourceOptions)` so that it *doesn't* provide
`-bootclasspath` when `$(JreRtJarPath)` is empty.

These three changes -- xamarin-android-tools bump, `<JdkInfo/>`
update, and `$(_JavacSourceOptions)` update -- allow `make all` to
build successfully.

Then we hit *unit* tests.  The above `javac` invocation has a warning:

	EXEC : warning : -parameters is not supported for target value 1.6. Use 1.8 or later.

Even though we've been using `javac -target 1.6 -parameters` for
*ages*, this combination is no longer supported.  In order to use
`javac -parameters` now, we need to use `javac -target 1.8`.

Update `$(JavacSourceVersion)` to 1.8 so that we can continue using
`javac -parameters`, which in turn requires that we update
`tests/Xamarin.Android.Tools.Bytecode-Tests` so that we expect the
newly updated `.class` file MajorVersion values.

[0]: https://bintray.com/jetbrains/intellij-jdk/download_file?file_path=jbrsdk-11_0_4-osx-x64-b546.1.tar.gz

Author: jonpryor

Directory.Build.props

@@ -43,10 +43,10 @@
     <XamarinAndroidToolsDirectory   Condition=" '$(XamarinAndroidToolsDirectory)' == '' ">$(MSBuildThisFileDirectory)external\xamarin-android-tools</XamarinAndroidToolsDirectory>
   </PropertyGroup>
   <PropertyGroup>
-    <JavacSourceVersion Condition=" '$(JavacSourceVersion)' == '' ">1.6</JavacSourceVersion>
-    <JavacTargetVersion Condition=" '$(JavacTargetVersion)' == '' ">1.6</JavacTargetVersion>
-    <JreRtJarPath Condition=" '$(JreRtJarPath)' == '' And '$(JavaCPath)' != '' ">$([System.IO.Path]::GetDirectoryName('$(JavaCPath)'))\..\jre\lib\rt.jar</JreRtJarPath>
-    <_JavacSourceOptions>-source $(JavacSourceVersion) -target $(JavacTargetVersion) -bootclasspath "$(JreRtJarPath)"</_JavacSourceOptions>
+    <JavacSourceVersion Condition=" '$(JavacSourceVersion)' == '' ">1.8</JavacSourceVersion>
+    <JavacTargetVersion Condition=" '$(JavacTargetVersion)' == '' ">1.8</JavacTargetVersion>
+    <_BootClassPath Condition=" '$(JreRtJarPath)' != '' ">-bootclasspath "$(JreRtJarPath)"</_BootClassPath>
+    <_JavacSourceOptions>-source $(JavacSourceVersion) -target $(JavacTargetVersion) $(_BootClassPath)</_JavacSourceOptions>
   </PropertyGroup>
   <PropertyGroup>
     <_XamarinAndroidCecilPath Condition=" '$(CecilSourceDirectory)' != '' And Exists('$(UtilityOutputFullPath)Xamarin.Android.Cecil.dll') ">$(UtilityOutputFullPath)Xamarin.Android.Cecil.dll</_XamarinAndroidCecilPath>

build-tools/Java.Interop.BootstrapTasks/Java.Interop.BootstrapTasks/JdkInfo.cs

@@ -17,10 +17,6 @@ namespace Java.Interop.BootstrapTasks
 {
 	public class JdkInfo : Task
 	{
-		const string JARSIGNER = "jarsigner.exe";
-		const string MDREG_KEY = @"SOFTWARE\Novell\Mono for Android";
-		const string MDREG_JAVA_SDK = "JavaSdkDirectory";
-
 		public  string  JdksRoot              { get; set; }
 
 		public  string  MaximumJdkVersion     { get; set; }
@@ -50,13 +46,18 @@ public override bool Execute ()
 				return false;
 			}
 
+			var rtJarPaths  = new[]{
+				Path.Combine (Path.GetDirectoryName (jdk.JavacPath), "..", "jre", "lib", "rt.jar"),
+			};
+			var rtJarPath   = rtJarPaths.FirstOrDefault (p => File.Exists (p));
+
 			JavaHomePath  = jdk.HomePath;
 
 			Directory.CreateDirectory (Path.GetDirectoryName (PropertyFile.ItemSpec));
 			Directory.CreateDirectory (Path.GetDirectoryName (MakeFragmentFile.ItemSpec));
 
-			WritePropertyFile (jdk.JarPath, jdk.JavacPath, jdk.JdkJvmPath, jdk.IncludePath);
-			WriteMakeFragmentFile (jdk.JarPath, jdk.JavacPath, jdk.JdkJvmPath, jdk.IncludePath);
+			WritePropertyFile (jdk.JarPath, jdk.JavacPath, jdk.JdkJvmPath, rtJarPath, jdk.IncludePath);
+			WriteMakeFragmentFile (jdk.JarPath, jdk.JavacPath, jdk.JdkJvmPath, rtJarPath, jdk.IncludePath);
 
 			return !Log.HasLoggedErrors;
 		}
@@ -92,7 +93,7 @@ Action<TraceLevel, string> CreateLogger ()
 			return logger;
 		}
 
-		void WritePropertyFile (string jarPath, string javacPath, string jdkJvmPath, IEnumerable<string> includes)
+		void WritePropertyFile (string jarPath, string javacPath, string jdkJvmPath, string rtJarPath, IEnumerable<string> includes)
 		{
 			var msbuild = XNamespace.Get ("http://schemas.microsoft.com/developer/msbuild/2003");
 			var project = new XElement (msbuild + "Project",
@@ -106,17 +107,28 @@ void WritePropertyFile (string jarPath, string javacPath, string jdkJvmPath, IEn
 					new XElement (msbuild + "JavaCPath", new XAttribute ("Condition", " '$(JavaCPath)' == '' "),
 						javacPath),
 					new XElement (msbuild + "JarPath", new XAttribute ("Condition", " '$(JarPath)' == '' "),
-						jarPath)));
+						jarPath),
+					CreateJreRtJarPath (msbuild, rtJarPath)));
 			project.Save (PropertyFile.ItemSpec);
 		}
 
-		void WriteMakeFragmentFile (string jarPath, string javacPath, string jdkJvmPath, IEnumerable<string> includes)
+		static XElement CreateJreRtJarPath (XNamespace msbuild, string rtJarPath)
+		{
+			if (rtJarPath == null)
+				return null;
+			return new XElement (msbuild + "JreRtJarPath",
+					new XAttribute ("Condition", " '$(JreRtJarPath)' == '' "),
+					rtJarPath);
+		}
+
+		void WriteMakeFragmentFile (string jarPath, string javacPath, string jdkJvmPath, string rtJarPath, IEnumerable<string> includes)
 		{
 			using (var o = new StreamWriter (MakeFragmentFile.ItemSpec)) {
 				o.WriteLine ($"export  JI_JAR_PATH          := {jarPath}");
 				o.WriteLine ($"export  JI_JAVAC_PATH        := {javacPath}");
 				o.WriteLine ($"export  JI_JDK_INCLUDE_PATHS := {string.Join (" ", includes)}");
 				o.WriteLine ($"export  JI_JVM_PATH          := {jdkJvmPath}");
+				o.WriteLine ($"export  JI_RT_JAR_PATH       := {rtJarPath}");
 			}
 		}
 	}

external/xamarin-android-tools

@@ -16,7 +16,7 @@ public void ClassFile_WithIJavaInterface_class ()
 		{
 			var c   = LoadClassFile (JavaType + ".class");
 			new ExpectedTypeDeclaration {
-				MajorVersion        = 0x32,
+				MajorVersion        = 0x34,
 				MinorVersion        = 0,
 				ConstantPoolCount   = 23,
 				AccessFlags         = ClassAccessFlags.Interface | ClassAccessFlags.Abstract,

tests/Xamarin.Android.Tools.Bytecode-Tests/IJavaInterfaceTests.cs

@@ -16,7 +16,7 @@ public void ClassFile_WithJavaAnnotation_class ()
 		{
 			var c   = LoadClassFile (JavaType + ".class");
 			new ExpectedTypeDeclaration {
-				MajorVersion        = 0x32,
+				MajorVersion        = 0x34,
 				MinorVersion        = 0,
 				ConstantPoolCount   = 23,
 				AccessFlags         = ClassAccessFlags.Public | ClassAccessFlags.Interface | ClassAccessFlags.Abstract | ClassAccessFlags.Annotation,

tests/Xamarin.Android.Tools.Bytecode-Tests/JavaAnnotationTests.cs

@@ -20,7 +20,7 @@ public void ClassFileDescription ()
 		{
 			var c   = LoadClassFile (JavaType + ".class");
 			new ExpectedTypeDeclaration {
-				MajorVersion        = 0x32,
+				MajorVersion        = 0x34,
 				MinorVersion        = 0,
 				ConstantPoolCount   = 53,
 				AccessFlags         = ClassAccessFlags.Final | ClassAccessFlags.Super | ClassAccessFlags.Enum,

tests/Xamarin.Android.Tools.Bytecode-Tests/JavaEnumTests.cs

@@ -16,7 +16,7 @@ public void ClassFileDescription ()
 		{
 			var c   = LoadClassFile (JavaType + ".class");
 			new ExpectedTypeDeclaration {
-				MajorVersion        = 0x32,
+				MajorVersion        = 0x34,
 				MinorVersion        = 0,
 				ConstantPoolCount   = 47,
 				AccessFlags         = ClassAccessFlags.Super,

tests/Xamarin.Android.Tools.Bytecode-Tests/JavaType.1Tests.cs

@@ -16,7 +16,7 @@ public void ClassFileDescription ()
 		{
 			var c   = LoadClassFile (JavaType + ".class");
 			new ExpectedTypeDeclaration {
-				MajorVersion        = 0x32,
+				MajorVersion        = 0x34,
 				MinorVersion        = 0,
 				ConstantPoolCount   = 23,
 				Deprecated          = true,

tests/Xamarin.Android.Tools.Bytecode-Tests/JavaType.ASCTests.cs

@@ -16,7 +16,7 @@ public void ClassFileDescription ()
 		{
 			var c   = LoadClassFile (JavaType + ".class");
 			new ExpectedTypeDeclaration {
-				MajorVersion        = 0x32,
+				MajorVersion        = 0x34,
 				MinorVersion        = 0,
 				ConstantPoolCount   = 20,
 				AccessFlags         = ClassAccessFlags.Public | ClassAccessFlags.Super | ClassAccessFlags.Abstract,

tests/Xamarin.Android.Tools.Bytecode-Tests/JavaType.PSCTests.cs

@@ -16,7 +16,7 @@ public void ClassFileDescription ()
 		{
 			var c   = LoadClassFile (JavaType + ".class");
 			new ExpectedTypeDeclaration {
-				MajorVersion        = 0x32,
+				MajorVersion        = 0x34,
 				MinorVersion        = 0,
 				ConstantPoolCount   = 46,
 				AccessFlags         = ClassAccessFlags.Public | ClassAccessFlags.Super | ClassAccessFlags.Abstract,