Forbid trait extending of final classes

lib/Trait.js

@@ -22,6 +22,7 @@
 var AbstractClass = require( './class_abstract' ),
     Class         = require( './class' ),
     ClassBuilder  = require( './ClassBuilder' ),
+    FinalClass    = require( './class_final' ),
     Interface     = require( './interface' );
 
 
@@ -123,9 +124,19 @@ Trait.extend = function()
         type    = _getTraitType( dfn ),
         isparam = ( type === 'param' );
 
-    if ( has_extend && !Class.isClass( extend ) )
+    if ( has_extend )
     {
-        throw TypeError( "Trait " + name + " cannot extend non-class" );
+        if ( !Class.isClass( extend ) )
+        {
+            throw TypeError( "Trait " + name + " cannot extend non-class" );
+        }
+        else if ( extend.___$$final$$ === true )
+        {
+            throw TypeError(
+                "Trait " + name + " cannot extend final class " +
+                    extend.toString()
+            )
+        }
     }
 
     // augment the parser to handle our own oddities

test/Trait/ClassExtendTest.js

@@ -25,6 +25,7 @@ require( 'common' ).testCase(
     {
         this.Sut           = this.require( 'Trait' );
         this.Class         = this.require( 'class' );
+        this.FinalClass    = this.require( 'class_final' );
 
         // nonsensical extend bases
         this.nonsense = [
@@ -259,4 +260,19 @@ require( 'common' ).testCase(
             _self.Sut.extend( _self.Sut( {} ), {} );
         }, TypeError );
     },
+
+
+    /**
+     * For consistency with the rest of the system, final classes are not
+     * permitted to be extended.
+     */
+    'Traits cannot extend final classes': function()
+    {
+        var _self = this;
+
+        this.assertThrows( function()
+        {
+            _self.Sut.extend( _self.FinalClass( {} ), {} );
+        }, TypeError );
+    },
 } );