(credit to Dr-Emman for the original code) - I just added some stuff to handle some of the cases encountered while generating the SWT externs.
Once you build the java-haxe-extern-creator jar - you can run it like this.
java -jar java-haxe-extern-creator.jar -source /path/to/swt/src -output path/to/externs/output/folder -packages org.eclipse.swt
Once completed it generates a class called AllThings.hx which you can use to find out if the compiler likes all the generated externs.
In the case of the mac version there are about 4 classes that need small patches made by hand. But the simple Webkit example compiles without requiring the manual patches.
Otherwise, I might try windows one next week when I have more time.
btw, if the extern generator outputs some errors - it's not always a problem - often just running the generation again will fix them - I think they might be to do with javadoc creation.