Overriding vanilla prototype methods no longer errors

This is something that I've been aware of for quite some time, but never got
around to fixing; ease.js had stalled until it was revitalized by becoming a
GNU project.

lib/MemberBuilder.js

@@ -120,11 +120,16 @@ exports.buildMethod = function(
     members, meta, name, value, keywords, instCallback, cid, base, state
 )
 {
+    // these defaults will be used whenever a keyword set is unavailable,
+    // which should only ever be the case if we're inheriting from a
+    // prototype rather than an ease.js class/etc
+    var kdefaults = this._methodKeywordDefaults;
+
     // TODO: We can improve performance by not scanning each one individually
     // every time this method is called
     var prev_data     = scanMembers( members, name, base ),
         prev          = ( prev_data ) ? prev_data.member : null,
-        prev_keywords = ( prev && prev.___$$keywords$$ ),
+        prev_keywords = ( prev && ( prev.___$$keywords$$ || kdefaults ) ),
         dest          = getMemberVisibility( members, keywords, name );
     ;
 
@@ -194,6 +199,13 @@ exports.buildMethod = function(
 };
 
 
+/**
+ * Default keywords to apply to methods inherited from a prototype.
+ * @type  {Object}
+ */
+exports._methodKeywordDefaults = { 'virtual': true };
+
+
 /**
  * Creates an abstract override super method proxy to NAME
  *

test/Class/InteropTest.js

@@ -0,0 +1,102 @@
+/**
+ * Tests class interoperability with vanilla ECMAScript
+ *
+ *  Copyright (C) 2014 Mike Gerwitz
+ *
+ *  This file is part of GNU ease.js.
+ *
+ *  ease.js is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Note that these tests all use the `new' keyword for instantiating
+ * classes, even though it is not required with ease.js; this is both for
+ * historical reasons (when `new' was required during early development) and
+ * because we are not testing (and do want to depend upon) that feature.
+ */
+
+require( 'common' ).testCase(
+{
+    caseSetUp: function()
+    {
+        this.Class = this.require( 'class' );
+    },
+
+
+    /**
+     * While this may seem at odds with ease.js' philosophy (because ease.js
+     * methods are *not* virtual by default), we do not have much choice in
+     * the matter: JavaScript is very lax and does not offer a way to
+     * declare something as virtual or otherwise. Given that, we have to
+     * choose between implicit virtual methods, or never allowing the user
+     * to override methods inherited from a prototype. The latter is not a
+     * wise choice, since there would be no way to change that behavior.
+     *
+     * Of course, if such a distinction were important, a wrapper class
+     * could be created that simply extends the prototype, marks methods
+     * virtual as appropriate, and retain only that reference for use from
+     * that point forward.
+     */
+    'Methods inherited from a prototype are implicitly virtual': function()
+    {
+        var expected = {};
+
+        var P = function()
+        {
+            this.foo = function()
+            {
+                return null;
+            };
+        }
+
+        var Class = this.Class,
+            inst;
+
+        // if an error is thrown here, then we're probably not virtual
+        this.assertDoesNotThrow( function()
+        {
+            inst = Class.extend( P,
+            {
+                'override foo': function()
+                {
+                    return expected;
+                }
+            } )();
+        } );
+
+        // the sky is falling if the above worked but this didn't
+        this.assertStrictEqual( inst.foo(), expected );
+    },
+
+
+    /**
+     * Complement to the above test.
+     */
+    'Prototype method overrides must provide override keyword': function()
+    {
+        var P = function()
+        {
+            this.foo = function() {};
+        };
+
+        var Class = this.Class;
+        this.assertThrows( function()
+        {
+            Class.extend( P,
+            {
+                // missing override keyword
+                foo: function() {},
+            } );
+        } );
+    },
+} );
+