we ran into some issues with Google Closure in our projects so we added a
RequestFilter that blacklists JS compression for some files by settings
the request to true based on regex-patterns.
Tapestry 5.5 update Google Closure to a version from 2017 (vs 2013 in 5.4)
but I'm not sure if it's configured for ES6 though, or with which version
Google Closure started supporting ES6.
An alternative approach (which we didn't use, blacklisting was good for us)
is replacing the minimizer with a custom version, it's contributed
ResourceMinimizer>) and should be overridable.