I prepared a patch to fix the problem that IFn's cannot be called with more than 20 arguments.
The corresponding test cases in apply_test.cljs had been commented out some years ago.
This most probably fixes meta functions, multi methods, spec functions and every IFn implementation out there.
These are corresponding tickets I found:
"mulitmethod apply with >20 args fails"
"with-meta doesn't work for variable arguments functions"
"High-arity .apply on spec-instrumented function throws "Invalid arity" error"
Maybe it also fixes/completed this one from 2012:
"compiler needs to put all args of an invocation after 20 into an array-seq"
This is the patch here; a single small commit:
It also removes a superfluous 'aclone' call (concat already makes a shallow clone).
I ran the tests with Nashorn, and the tests that were previously commented out succeed now.
I signed the Contributors Agreement in 2016, but after signing up to the JIRA now, it says that I don't have 'access to Jira on clojure.atlassian.net', which is why I start with this question here.
Hoping this gets though, as I was basically waiting for this to be fixed for years now.