Fixes #5955. Option crossDomain now forces ajax to consider a request as cross-domain even when it is not. Useful for when servers issue redirects to cross-domain urls. Unit test added.

src/ajax.js

@@ -520,12 +520,15 @@ jQuery.extend({
 		// Determine if a cross-domain request is in order
 		var parts = rurl.exec( s.url.toLowerCase() ),
 			loc = location;
-		s.crossDomain = !!(
+
-				parts &&
+		if ( ! s.crossDomain ) {
-				( parts[ 1 ] && parts[ 1 ] != loc.protocol ||
+			s.crossDomain = !!(
-					parts[ 2 ] != loc.hostname ||
+					parts &&
-					( parts[ 3 ] || 80 ) != ( loc.port || 80 ) )
+					( parts[ 1 ] && parts[ 1 ] != loc.protocol ||
-		);
+						parts[ 2 ] != loc.hostname ||
+						( parts[ 3 ] || 80 ) != ( loc.port || 80 ) )
+			);
+		}
 
 		// Convert data if not already a string
 		if ( s.data && s.processData && typeof s.data != "string" ) {

test/unit/ajax.js

@@ -383,14 +383,15 @@ test(".ajax() - hash", function() {
 
 test("jQuery ajax - cross-domain detection", function() {
 
-	expect( 3 );
+	expect( 4 );
 
 	var loc = document.location,
 		otherPort = loc.port === 666 ? 667 : 666,
 		otherProtocol = loc.protocol === "http:" ? "https:" : "http:",
 		protocolFlag,
 		hostFlag,
-		portFlag;
+		portFlag,
+		forcedFlag;
 
 	if ( jQuery.ajax({
 		url: otherProtocol + "//" + loc.host,
@@ -431,6 +432,20 @@ test("jQuery ajax - cross-domain detection", function() {
 		}
 	}
 
+	if ( jQuery.ajax({
+		url: loc.protocol + "//" + loc.host,
+		crossDomain: true,
+		beforeSend: function( _ , s ) {
+			forcedFlag = 1;
+			ok( s.crossDomain , "Test forced crossDomain is detected as cross-domain" );
+			return false;
+		}
+	}) === false ) {
+		if ( ! forcedFlag ) {
+			ok( ! jQuery.support.cors , "Test forced crossDomain is detected as cross-domain (no transport)" );
+		}
+	}
+
 });
 
 test(".ajax() - 304", function() {