(require '[clojure.spec.alpha :as s])
  
  (s/def ::not-in-map-spec pos-int?)
  (s/def ::in-map-spec string?) 
  (s/def ::the-map 
    (s/keys :req [::in-map-spec]))
  
  (def m 
    {::in-map-spec     "yes"
     ::not-in-map-spec -13})
  
  (s/valid? ::the-map m) ; => false
  (s/explain ::the-map m) ; => -13 - failed: pos-int? in: [:user/not-in-map-spec]

This surprises me, that a key that’s not in my spec, makes the spec invalid?

This is covered in the docstring for s/keys - all keys are checked

Hmm. That’s a conundrum in my usage, which I assume questions my usage: I have a big-map. I want to grab a part of it and save it away. Then use the rest to flow along. I can’t grab a part of it, because the rest is invalid. Do I explicitly select-keys to save it away?

Yes, you can do that

(s/def :demo/m1 (s/keys :req-un [::a ::b ::c ::d ::e]))

(s/def :demo/m2 (s/keys :req-un [::a ::b ::c]))

spec is not a transformation engine, it's a validation/verification library

or are you asking about spec transformation

assuming so, not really, it really encourages building up by composition, not by taking away

I meant spec transformation, yes. I'm writing generative tests based on some s/keys specs and I'll have to dissoc some of the keys after the generation anyway, so I wondered if I could skip that step. Definitely not a deal-breaker and the justification behind the design decision is sound, as always. Thanks. 🙂