it turns out that the sbt/web-plugin configuration i described in my last post is not quite cutting it. what we observed is that while changes to the contents of the webapp subtree were indeed effective immediately¹ sbt commands like prepare-webapp and jetty-reload would sometimes work and sometimes just ignore us.

so, back to digging around in the web-plugin sources and this is what we are now using:

this sbt configuration tells jetty to run out of the src/main/webapp directory — any changes you do in there will become effective immediately and prepare-webapp and jetty-reload are working as expected. the drawback is that your generated classes and lib files get copied to src/main/webapp/WEB-INF :-( i know, sucks, but still better than having to restart your webapp everytime you change a {html,css,js} file. if you are using git you might want to add

src/main/webapp/WEB-INF/lib/*
src/main/webapp/WEB-INF/classes/*

to your top-level .gitignore file.