Automatically infer rest arg as having seq type
no type will be inferred for the xs param. If we instead infer it to be of type seq then an unchecked if can be emitted. (An example of code like this involving an unnecessary check in if is in the variadic arity of str.)
While a change such as this wouldn't have a huge perf impact, it could slightly reduce generated code size and it could lead to better diagnostics for incorrect code:
CLJS-2961.patch added to Patch Tender
CLJS-2961.patch passes CI and Canary, and shows no compiler slowdown when compiling Coal Mine.