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

Conflicts:
	src/attributes/attr.js

src/attributes/attr.js

@@ -6,7 +6,8 @@ define([
 	"../support"
 ], function( jQuery, rnotwhite, strundefined ) {
 
-var nodeHook, boolHook;
+var nodeHook, boolHook,
+	attrHandle = jQuery.expr.attrHandle;
 
 jQuery.fn.extend({
 	attr: function( name, value ) {
@@ -120,23 +121,19 @@ boolHook = {
 	}
 };
 jQuery.each( jQuery.expr.match.bool.source.match( /\w+/g ), function( i, name ) {
-	var getter = jQuery.expr.attrHandle[ name ] || jQuery.find.attr;
-
-	jQuery.expr.attrHandle[ name ] = function( elem, name, isXML ) {
-		var fn = jQuery.expr.attrHandle[ name ],
-			ret = isXML ?
-				undefined :
-				/* jshint eqeqeq: false */
-				// Temporarily disable this handler to check existence
-				(jQuery.expr.attrHandle[ name ] = undefined) !=
-					getter( elem, name, isXML ) ?
-
-					name.toLowerCase() :
-					null;
-
-		// Restore handler
-		jQuery.expr.attrHandle[ name ] = fn;
-
+	var getter = attrHandle[ name ] || jQuery.find.attr;
+
+	attrHandle[ name ] = function( elem, name, isXML ) {
+		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 ] = handle;
+		}
 		return ret;
 	};
 });

test/unit/attributes.js

@@ -470,6 +470,20 @@ 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(),