[Java.Interop, generator] Fix GetPeerMembers for interfaces (#486)

Context: dotnet/android#3533
Consider the following Java interface which contains a default
interface method:
// Java
package com.xamarin.android;
public interface DefaultMethodsInterface
{
default int foo () { return 0; }
}
This is bound as:
// C# Binding
public partial interface IDefaultMethodsInterface : IJavaPeerable {
static readonly JniPeerMembers _members = new JniPeerMembers (
"java/DefaultMethodsInterface",
typeof (IDefaultMethodsInterface));
[Register ("foo", "()V", "…")]
virtual unsafe int Foo ()
{
return _members.InstanceMethods.InvokeVirtualInt32Method ("foo.()V", this, null);
}
}
If we "implement" the interface from C# *without* implementing
`IDefaultMethodsInterface.Foo()`:
// C#
class ManagedOverrideDefault : Java.Lang.Object, IDefaultMethodsInterface
{
}
Then invoke the default interface method:
var over = new ManagedOverrideDefault ();
(over as IDefaultMethodsInterface).Foo ();
The attempt to invoke the default implementation of
`IDefaultMethodsInterface.Foo()` causes a crash:
Java.Lang.NoSuchMethodError : no non-static method "Ljava/lang/Object;.foo()I"
The cause of the crash is as follows: `IDefaultMethodsInterface.Foo()`
calls `JniPeerMembers.JniInstanceMethods.InvokeVirtualInt32Method()`
tries to determine if the method is overridden, and if the method is
*not* overridden -- as is the case here -- then we hit the non-virtual
invocation path:
// src/Java.Interop/Java.Interop/JniPeerMembers.JniInstanceMethods_Invoke.cs
var j = Members.GetPeerMembers (self);
var n = j.InstanceMethods.GetMethodInfo (encodedMember);
return JniEnvironment.InstanceMethods.CallNonvirtualIntMethod (self.PeerReference, j.JniPeerType.PeerReference, n, parameters);
`JniInstanceMethods.Members` will be the
`IDefaultMethodsInterface._members` field, and
`Members.GetPeerMembers()` would return `self.JniPeerMembers`.
Because this is a C# class which inherits `Java.Lang.Object`,
`Java.Lang.Object._members` is returned. We then attempt to resolve
`foo()` from `java.lang.Object`, which *does not exist*, which is why
the `NoSuchMethodError` is thrown.
The fix is to "intercept" the `Members.GetPeerMembers()` invocation
so that `j` refers to `IDefaultMethodsInterface._members`, *not*
`Java.Lang.Object._members`. This would allow `n` to refer to
`DefaultMethodsInterface.foo()`, which *does* exist, and *can* be
invoked via `JniEnvironment.InstanceMethods.CallNonvirtualIntMethod()`.
Add the following `JniPeerMembers` constructor overload:
partial class JniPeerMembers {
public JniPeerMembers (string jniPeerTypeName, Type managedPeerType, bool isInterface);
}
Update `JniPeerMembers.GetPeerMembers()` so that if `isInterface` is
true, we return `this` (the *interface*s `JniPeerMembers` instance).
Update `generator` so that `_members` construction within interfaces
sets the `isInterface` parameter to true, resulting in:
partial interface IDefaultMethodsInterface {
static readonly JniPeerMembers _members = new JniPeerMembers (
"java/DefaultMethodsInterface",
typeof (IDefaultMethodsInterface),
isInterface: true);
}
This allows `(over as IDefaultMethodsInterface).Foo()` to work
without an exception being thrown.

Author: jpobst

gendarme-ignore.txt

@@ -351,6 +351,7 @@ T: Java.Interop.JniInt32ArrayElements
 T: Java.Interop.JniInt64ArrayElements
 T: Java.Interop.JniLocationException
 T: Java.Interop.JniMethodInfo
+T: Java.Interop.JniPeerMembers
 T: Java.Interop.JniSByteArrayElements
 T: Java.Interop.JniSingleArrayElements
 T: Java.Interop.JniType

src/Java.Interop/Java.Interop/JniPeerMembers.cs

@@ -7,8 +7,15 @@ namespace Java.Interop {
 
 publicpartialclassJniPeerMembers{
 
+privateboolisInterface;
+
+publicJniPeerMembers(stringjniPeerTypeName,TypemanagedPeerType,boolisInterface)
+:this(jniPeerTypeName,managedPeerType,checkManagedPeerType:true,isInterface:isInterface)
+{
+}
+
 publicJniPeerMembers(stringjniPeerTypeName,TypemanagedPeerType)
-:this(jniPeerTypeName,managedPeerType,checkManagedPeerType:true)
+:this(jniPeerTypeName,managedPeerType,checkManagedPeerType:true,isInterface:false)
 {
 if(managedPeerType==null)
 thrownewArgumentNullException("managedPeerType");
@@ -27,7 +34,7 @@ public JniPeerMembers (string jniPeerTypeName, Type managedPeerType)
 ManagedPeerType=managedPeerType;
 }
 
-JniPeerMembers(stringjniPeerTypeName,TypemanagedPeerType,boolcheckManagedPeerType)
+JniPeerMembers(stringjniPeerTypeName,TypemanagedPeerType,boolcheckManagedPeerType,boolisInterface=false)
 {
 if(jniPeerTypeName==null)
 thrownewArgumentNullException(nameof(jniPeerTypeName));
@@ -51,6 +58,8 @@ public JniPeerMembers (string jniPeerTypeName, Type managedPeerType)
 JniPeerTypeName=jniPeerTypeName;
 ManagedPeerType=managedPeerType;
 
+this.isInterface=isInterface;
+
 instanceMethods=newJniInstanceMethods(this);
 instanceFields=newJniInstanceFields(this);
 staticMethods=newJniStaticMethods(this);
@@ -140,7 +149,7 @@ protected virtual bool UsesVirtualDispatch (IJavaPeerable value, Type declaringT
 
 protectedvirtualJniPeerMembersGetPeerMembers(IJavaPeerablevalue)
 {
-returnvalue.JniPeerMembers;
+returnisInterface?this:value.JniPeerMembers;
 }
 
 internalstaticvoidAssertSelf(IJavaPeerableself)

tools/generator/Java.Interop.Tools.Generator.CodeGeneration/JavaInteropCodeGenerator.cs

@@ -29,7 +29,7 @@ static string GetInvokeType (string type)
 
 internaloverridevoidWriteClassHandle(ClassGentype,stringindent,boolrequireNew)
 {
-WritePeerMembers(indent+'\t',true,requireNew,type.RawJniName,type.Name);
+WritePeerMembers(indent+'\t',true,requireNew,type.RawJniName,type.Name,false);
 
 writer.WriteLine("{0}\tinternal static {1}IntPtr class_ref {{",indent,requireNew?"new ":string.Empty);
 writer.WriteLine("{0}\t\tget {{",indent);
@@ -55,12 +55,12 @@ internal override void WriteClassHandle (ClassGen type, string indent, bool requ
 
 internaloverridevoidWriteClassHandle(InterfaceGentype,stringindent,stringdeclaringType)
 {
-WritePeerMembers(indent,false,true,type.RawJniName,declaringType);
+WritePeerMembers(indent,false,true,type.RawJniName,declaringType,type.Name==declaringType);
 }
 
 internaloverridevoidWriteClassInvokerHandle(ClassGentype,stringindent,stringdeclaringType)
 {
-WritePeerMembers(indent,true,true,type.RawJniName,declaringType);
+WritePeerMembers(indent,true,true,type.RawJniName,declaringType,false);
 
 writer.WriteLine();
 writer.WriteLine("{0}public override global::Java.Interop.JniPeerMembers JniPeerMembers {{",indent);
@@ -75,7 +75,7 @@ internal override void WriteClassInvokerHandle (ClassGen type, string indent, st
 
 internaloverridevoidWriteInterfaceInvokerHandle(InterfaceGentype,stringindent,stringdeclaringType)
 {
-WritePeerMembers(indent,true,true,type.RawJniName,declaringType);
+WritePeerMembers(indent,true,true,type.RawJniName,declaringType,false);
 
 writer.WriteLine();
 writer.WriteLine("{0}static IntPtr java_class_ref {{",indent);
@@ -262,10 +262,10 @@ internal override void WriteFieldSetBody (Field field, string indent, GenBase ty
 writer.WriteLine("{0}}}",indent);
 }
 
-voidWritePeerMembers(stringindent,boolisInternal,boolisNew,stringrawJniType,stringdeclaringType)
+voidWritePeerMembers(stringindent,boolisInternal,boolisNew,stringrawJniType,stringdeclaringType,boolisInterface)
 {
 varsignature=$"{(isInternal?"internal ":"")}static {(isNew?"new ":"")}readonly JniPeerMembers _members = ";
-vartype=$"new {GetPeerMembersType()} (\"{rawJniType}\", typeof ({declaringType}));";
+vartype=$"new {GetPeerMembersType()} (\"{rawJniType}\", typeof ({declaringType}){(isInterface?", isInterface: true":string.Empty)});";
 
 writer.WriteLine($"{indent}{signature}{type}");
 }

tools/generator/Tests/Unit-Tests/CodeGeneratorExpectedResults/JavaInterop1/WriteInterfaceDefaultMethod.txt

@@ -1,7 +1,7 @@
 // Metadata.xml XPath interface reference: path="/api/package[@name='java.code']/interface[@name='IMyInterface']"
 [Register ("java/code/IMyInterface", "", "java.code.IMyInterfaceInvoker")]
 public partial interface IMyInterface : IJavaObject, IJavaPeerable {
-	static new readonly JniPeerMembers _members = new JniPeerMembers ("java/code/IMyInterface", typeof (IMyInterface));
+	static new readonly JniPeerMembers _members = new JniPeerMembers ("java/code/IMyInterface", typeof (IMyInterface), isInterface: true);
 
 	static Delegate cb_DoSomething;
 #pragma warning disable 0169

tools/generator/Tests/Unit-Tests/CodeGeneratorExpectedResults/JavaInterop1/WriteInterfaceDefaultProperty.txt

@@ -1,7 +1,7 @@
 // Metadata.xml XPath interface reference: path="/api/package[@name='java.code']/interface[@name='IMyInterface']"
 [Register ("java/code/IMyInterface", "", "java.code.IMyInterfaceInvoker")]
 public partial interface IMyInterface : IJavaObject, IJavaPeerable {
-	static new readonly JniPeerMembers _members = new JniPeerMembers ("java/code/IMyInterface", typeof (IMyInterface));
+	static new readonly JniPeerMembers _members = new JniPeerMembers ("java/code/IMyInterface", typeof (IMyInterface), isInterface: true);
 
 	static Delegate cb_get_Value;
 #pragma warning disable 0169

tools/generator/Tests/Unit-Tests/CodeGeneratorExpectedResults/JavaInterop1/WriteInterfaceDefaultPropertyGetterOnly.txt

@@ -1,7 +1,7 @@
 // Metadata.xml XPath interface reference: path="/api/package[@name='java.code']/interface[@name='IMyInterface']"
 [Register ("java/code/IMyInterface", "", "java.code.IMyInterfaceInvoker")]
 public partial interface IMyInterface : IJavaObject, IJavaPeerable {
-	static new readonly JniPeerMembers _members = new JniPeerMembers ("java/code/IMyInterface", typeof (IMyInterface));
+	static new readonly JniPeerMembers _members = new JniPeerMembers ("java/code/IMyInterface", typeof (IMyInterface), isInterface: true);
 
 	static Delegate cb_get_Value;
 #pragma warning disable 0169

tools/generator/Tests/Unit-Tests/CodeGeneratorExpectedResults/XAJavaInterop1/WriteInterfaceDefaultMethod.txt

@@ -1,7 +1,7 @@
 // Metadata.xml XPath interface reference: path="/api/package[@name='java.code']/interface[@name='IMyInterface']"
 [Register ("java/code/IMyInterface", "", "java.code.IMyInterfaceInvoker")]
 public partial interface IMyInterface : IJavaObject, IJavaPeerable {
-	static new readonly JniPeerMembers _members = new XAPeerMembers ("java/code/IMyInterface", typeof (IMyInterface));
+	static new readonly JniPeerMembers _members = new XAPeerMembers ("java/code/IMyInterface", typeof (IMyInterface), isInterface: true);
 
 	static Delegate cb_DoSomething;
 #pragma warning disable 0169

tools/generator/Tests/Unit-Tests/CodeGeneratorExpectedResults/XAJavaInterop1/WriteInterfaceDefaultProperty.txt

@@ -1,7 +1,7 @@
 // Metadata.xml XPath interface reference: path="/api/package[@name='java.code']/interface[@name='IMyInterface']"
 [Register ("java/code/IMyInterface", "", "java.code.IMyInterfaceInvoker")]
 public partial interface IMyInterface : IJavaObject, IJavaPeerable {
-	static new readonly JniPeerMembers _members = new XAPeerMembers ("java/code/IMyInterface", typeof (IMyInterface));
+	static new readonly JniPeerMembers _members = new XAPeerMembers ("java/code/IMyInterface", typeof (IMyInterface), isInterface: true);
 
 	static Delegate cb_get_Value;
 #pragma warning disable 0169

tools/generator/Tests/Unit-Tests/CodeGeneratorExpectedResults/XAJavaInterop1/WriteInterfaceDefaultPropertyGetterOnly.txt

@@ -1,7 +1,7 @@
 // Metadata.xml XPath interface reference: path="/api/package[@name='java.code']/interface[@name='IMyInterface']"
 [Register ("java/code/IMyInterface", "", "java.code.IMyInterfaceInvoker")]
 public partial interface IMyInterface : IJavaObject, IJavaPeerable {
-	static new readonly JniPeerMembers _members = new XAPeerMembers ("java/code/IMyInterface", typeof (IMyInterface));
+	static new readonly JniPeerMembers _members = new XAPeerMembers ("java/code/IMyInterface", typeof (IMyInterface), isInterface: true);
 
 	static Delegate cb_get_Value;
 #pragma warning disable 0169