This code is invalid but worked prior to 1.9.655. We don't currently warn on variadic implementations and this triggers the compiler to generate a variadic method.
The user will see a cryptic error about `self__` not being defined when attempting to leverage this invalid pattern.
Issue seems to be reagent that uses variadic IFn:
Possibly a regression of: CLJS-1445
There is no such thing as variadic IFn or variadic protocols at all.
See CLJS-2134, which will emit a new diagnostic in this scenario.
This relevant code in reagent has been fixed with https://github.com/reagent-project/reagent/commit/3cf045dc8264373d93d9c3a7607dc2a349194681#diff-9ca1adc3660082ab6f20b66f7c7a911c and was released with 0.7.0 (2017-06-27)