Ajax: Do not execute scripts for unsuccessful HTTP responses

The script transport used to evaluate fetched script sources which is
undesirable for unsuccessful HTTP responses. This is different to other data
types where such a convention was fine (e.g. in case of JSON).

Fixes gh-4250
Closes gh-4379

src/ajax.js

@@ -748,6 +748,11 @@ jQuery.extend( {
 				response = ajaxHandleResponses( s, jqXHR, responses );
 			}
 
+			// Use a noop converter for missing script
+			if ( !isSuccess && jQuery.inArray( "script", s.dataTypes ) > -1 ) {
+				s.converters[ "text script" ] = function() {};
+			}
+
 			// Convert no matter what (that way responseXXX fields are always set)
 			response = ajaxConvert( s, response, jqXHR, isSuccess );
 

test/data/mock.php

@@ -216,6 +216,19 @@ QUnit.assert.ok( true, "mock executed");';
 		unlink( $this->cspFile );
 	}
 
+	protected function errorWithScript( $req ) {
+		header( 'HTTP/1.0 404 Not Found' );
+		if ( isset( $req->query['withScriptContentType'] ) ) {
+			header( 'Content-Type: application/javascript' );
+		}
+		if ( isset( $req->query['callback'] ) ) {
+			$callback = $req->query['callback'];
+			echo $callback . '( {"status": 404, "msg": "Not Found"} )';
+		} else {
+			echo 'QUnit.assert.ok( false, "Mock return erroneously executed" );';
+		}
+	}
+
 	public function __construct() {
 		$this->cspFile = __DIR__ . '/support/csp.log';
 	}

test/middleware-mockserver.js

@@ -226,6 +226,18 @@ var mocks = {
 		cspLog = "";
 		resp.writeHead( 200 );
 		resp.end();
+	},
+	errorWithScript: function( req, resp ) {
+		if ( req.query.withScriptContentType ) {
+			resp.writeHead( 404, { "Content-Type": "application/javascript" } );
+		} else {
+			resp.writeHead( 404 );
+		}
+		if ( req.query.callback ) {
+			resp.end( req.query.callback + "( {\"status\": 404, \"msg\": \"Not Found\"} )" );
+		} else {
+			resp.end( "QUnit.assert.ok( false, \"Mock return erroneously executed\" );" );
+		}
 	}
 };
 var handlers = {

test/unit/ajax.js

@@ -806,6 +806,121 @@ QUnit.module( "ajax", {
 		};
 	} );
 
+	ajaxTest( "jQuery.ajax() - do not execute scripts from unsuccessful responses (gh-4250)", 11, function( assert ) {
+		var globalEval = jQuery.globalEval;
+
+		var failConverters = {
+			"text script": function() {
+				assert.ok( false, "No converter for unsuccessful response" );
+			}
+		};
+
+		function request( title, options ) {
+			var testMsg = title + ": expected file missing status";
+			return jQuery.extend( {
+				beforeSend: function() {
+					jQuery.globalEval = function() {
+						assert.ok( false, "Should not eval" );
+					};
+				},
+				complete: function() {
+					jQuery.globalEval = globalEval;
+				},
+				// error is the significant assertion
+				error: function( xhr ) {
+					assert.strictEqual( xhr.status, 404, testMsg );
+				},
+				success: function() {
+					assert.ok( false, "Unanticipated success" );
+				}
+			}, options );
+		}
+
+		return [
+			request(
+				"HTML reply",
+				{
+					url: url( "404.txt" )
+				}
+			),
+			request(
+				"HTML reply with dataType",
+				{
+					dataType: "script",
+					url: url( "404.txt" )
+				}
+			),
+			request(
+				"script reply",
+				{
+					url: url( "mock.php?action=errorWithScript&withScriptContentType" )
+				}
+			),
+			request(
+				"non-script reply",
+				{
+					url: url( "mock.php?action=errorWithScript" )
+				}
+			),
+			request(
+				"script reply with dataType",
+				{
+					dataType: "script",
+					url: url( "mock.php?action=errorWithScript&withScriptContentType" )
+				}
+			),
+			request(
+				"non-script reply with dataType",
+				{
+					dataType: "script",
+					url: url( "mock.php?action=errorWithScript" )
+				}
+			),
+			request(
+				"script reply with converter",
+				{
+					converters: failConverters,
+					url: url( "mock.php?action=errorWithScript&withScriptContentType" )
+				}
+			),
+			request(
+				"non-script reply with converter",
+				{
+					converters: failConverters,
+					url: url( "mock.php?action=errorWithScript" )
+				}
+			),
+			request(
+				"script reply with converter and dataType",
+				{
+					converters: failConverters,
+					dataType: "script",
+					url: url( "mock.php?action=errorWithScript&withScriptContentType" )
+				}
+			),
+			request(
+				"non-script reply with converter and dataType",
+				{
+					converters: failConverters,
+					dataType: "script",
+					url: url( "mock.php?action=errorWithScript" )
+				}
+			),
+			request(
+				"JSONP reply with dataType",
+				{
+					dataType: "jsonp",
+					url: url( "mock.php?action=errorWithScript" ),
+					beforeSend: function() {
+						jQuery.globalEval = function( response ) {
+							assert.ok( /"status": 404, "msg": "Not Found"/.test( response ), "Error object returned" );
+						};
+					}
+				}
+			)
+		];
+	} );
+
 	ajaxTest( "jQuery.ajax() - synchronous request", 1, function( assert ) {
 		return {
 			url: url( "json_obj.js" ),