Initial trait virtual member proxy implementation

This has some flaws that should be addressed, but those will be detailed in
later commits; this works for now.

lib/MethodWrappers.js

@@ -123,6 +123,9 @@ exports.standard = {
                 : retval;
         };
 
+        // TODO: need a test for this; yes, we want to store a reference
+        ret.___$$proxy_to$$ = proxy_to;
+
         // ensures that proxies can be used to provide concrete
         // implementations of abstract methods with param requirements (we
         // have no idea what we'll be proxying to at runtime, so we need to

lib/Trait.js

@@ -132,10 +132,63 @@ function createConcrete( acls )
         dfn[ vis + ' proxy ' + f ] = '___$$pmo$$';
     }
 
+    // virtual methods need to be handled with care to ensure that we invoke
+    // any overrides
+    createVirtProxy( acls, dfn );
+
     return acls.extend( dfn );
 }
 
 
+/**
+ * Create virtual method proxies for all virtual members
+ *
+ * Virtual methods are a bit of hassle with traits: we are in a situation
+ * where we do not know at the time that the trait is created whether or not
+ * the virtual method has been overridden, since the class that the trait is
+ * mixed into may do the overriding. Therefore, we must check if an override
+ * has occured *when the method is invoked*; there is room for optimization
+ * there (by making such a determination at the time of mixin), but we'll
+ * leave that for later.
+ *
+ * @param  {AbstractClass}  acls  abstract trait class
+ * @param  {Object}         dfn   destination definition object
+ *
+ * @return  {undefined}
+ */
+function createVirtProxy( acls, dfn )
+{
+    var vmembers = ClassBuilder.getMeta( acls ).virtualMembers;
+
+    // f = `field'
+    for ( var f in vmembers )
+    {
+        var vis = ( acls.___$$methods$$['public'][ f ] !== undefined )
+            ? 'public'
+            : 'protected';
+
+        dfn[ vis + ' virtual override ' + f ] = ( function()
+        {
+            // this is the aforementioned proxy method; see the docblock for
+            // more information
+            return function()
+            {
+                var pmo = this.___$$pmo$$,
+                    o   = pmo[ f ],
+                    op  = o.___$$proxy_to$$;
+
+                // XXX: a better way to do this would be nice, since this
+                // does a substring check on every call; avoids infinite
+                // recursion from proxying to self
+                return ( o && !( op && op.substr( 0, 7 ) === '___$to$' ) )
+                    ? pmo[ f ].apply( pmo, arguments )
+                    : this.__super.apply( this, arguments );
+            }
+        } )( f );
+    }
+}
+
+
 /**
  * Mix trait into the given definition
  *

test/Trait/VirtualTest.js

@@ -97,4 +97,41 @@ require( 'common' ).testCase(
 
         this.assertEqual( C().foo(), expected );
     },
+
+
+    /**
+     * If C uses T and overrides T.Ma, and there is some method T.Mb that
+     * invokes T.Ma, then T.Mb should instead invoke C.Ma.
+     */
+    'Class-overridden virtual trait method is accessible by trait':
+    function()
+    {
+        var _self = this;
+
+        var T = this.Sut(
+        {
+            'public doFoo': function()
+            {
+                // should call overridden, not the one below
+                this.foo();
+            },
+
+            // to be overridden
+            'virtual protected foo': function()
+            {
+                _self.fail( true, false, "Method not overridden." );
+            },
+        } );
+
+        var called = false;
+
+        var C = this.Class.use( T ).extend(
+        {
+            // should be called by T.doFoo
+            'override protected foo': function() { called = true },
+        } );
+
+        C().doFoo();
+        this.assertOk( called );
+    },
 } );