Can't speak to intention, but that predicate has an invariant assumption: that the arg is a collection. Neither true nor false would be valid answers. The error can be avoided by first checking that the invariant assumption holds:

user=> (s/valid? (s/and coll? empty?) 1)
false

Is it possible to dynamically generate specs at runtime? For example, based on a runtime value, I call a fn that returns a vector of namespaced keys. I then generate a spec like (s/keys :req vector-of-keys). Since keys is a macro, I haven’t been able to find a way

you'll need to eval somehow, either by explicitly using eval or by wrapping in another macro that uses backtick

(in spec 2, we've made this much easier)

Great, looking forward to spec2