Fix for custom attr handles duck-punching the boolean attr handle

src/attributes/attr.js

@@ -145,17 +145,19 @@ boolHook = {
 // Retrieve booleans specially
 jQuery.each( jQuery.expr.match.bool.source.match( /\w+/g ), function( i, name ) {
 
-	var getter = attrHandle[ name ] || jQuery.find.attr,
-	fn = attrHandle[ name ] = getSetInput && getSetAttribute || !ruseDefault.test( name ) ?
+	var getter = attrHandle[ name ] || jQuery.find.attr;
+
+	attrHandle[ name ] = getSetInput && getSetAttribute || !ruseDefault.test( name ) ?
 		function( elem, name, isXML ) {
-			var ret;
+			var ret, handle;
 			if ( !isXML ) {
 				// Avoid an infinite loop by temporarily removing this function from the getter
+				handle = attrHandle[ name ];
 				attrHandle[ name ] = ret;
 				ret = getter( elem, name, isXML ) != null ?
 					name.toLowerCase() :
 					null;
-				attrHandle[ name ] = fn;
+				attrHandle[ name ] = handle;
 			}
 			return ret;
 		} :

test/unit/attributes.js

@@ -473,6 +473,20 @@ test( "attr(String, Object)", function() {
 	equal( jQuery("#name").attr( "nonexisting", undefined ).attr("nonexisting"), undefined, ".attr('attribute', undefined) does not create attribute (#5571)" );
 });
 
+test( "attr - extending the boolean attrHandle", function() {
+	expect( 1 );
+	var called = false,
+		_handle = jQuery.expr.attrHandle.checked || $.noop;
+	jQuery.expr.attrHandle.checked = function() {
+		called = true;
+		_handle.apply( this, arguments );
+	};
+	jQuery( "input" ).attr( "checked" );
+	called = false;
+	jQuery( "input" ).attr( "checked" );
+	ok( called, "The boolean attrHandle does not drop custom attrHandles" );
+});
+
 test( "attr(String, Object) - Loaded via XML document", function() {
 	expect( 2 );
 	var xml = createDashboardXML(),