Clarify why BoxedValue should not support invokeMember() and readMember()

Author: eregon

spec/truffle/interop/polyglot/foreign_number_spec.rb

@@ -70,4 +70,10 @@
       (foreign ** 2).should == (ruby ** 2)
     end
   end
+
+  it "does not support odd? yet" do
+    @numbers.each do |foreign, _ruby|
+      -> { foreign.odd? }.should raise_error(Polyglot::UnsupportedMessageError)
+    end
+  end
 end

src/main/java/org/truffleruby/interop/BoxedValue.java

@@ -12,11 +12,13 @@
 import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
 import com.oracle.truffle.api.interop.InteropLibrary;
 import com.oracle.truffle.api.interop.TruffleObject;
-import com.oracle.truffle.api.interop.UnsupportedMessageException;
+import com.oracle.truffle.api.library.CachedLibrary;
 import com.oracle.truffle.api.library.ExportLibrary;
 import com.oracle.truffle.api.library.ExportMessage;
 import com.oracle.truffle.api.library.Message;
 import com.oracle.truffle.api.library.ReflectionLibrary;
+import org.truffleruby.RubyContext;
+import org.truffleruby.language.control.RaiseException;
 
 @ExportLibrary(ReflectionLibrary.class)
 public class BoxedValue implements TruffleObject {
@@ -32,11 +34,13 @@ public BoxedValue(Object value) {
 
     @TruffleBoundary
     @ExportMessage
-    protected Object send(Message message, Object[] args) throws Exception {
-        if (message == READ_MEMBER) {
-            throw UnsupportedMessageException.create();
-        } else if (message == INVOKE_MEMBER) {
-            throw UnsupportedMessageException.create();
+    protected Object send(Message message, Object[] args,
+            @CachedLibrary("this") ReflectionLibrary node) throws Exception {
+        if (message == READ_MEMBER || message == INVOKE_MEMBER) {
+            RubyContext context = RubyContext.get(node);
+            throw new RaiseException(context, context.getCoreExceptions().unsupportedMessageError(
+                    "Methods should not be called on a BoxedValue as that would expose the potential Ruby object behind rather than relying on interop messages",
+                    node));
         }
         ReflectionLibrary reflection = ReflectionLibrary.getFactory().getUncached();
         return reflection.send(value, message, args);