On Tuesday, August 23, 2016 at 3:27:28 AM UTC+2, Alex Miller wrote:
>
> predicate: (cat :args (* :clojure.core.specs/binding-form) :varargs (?
> (cat :amp #{(quote &)} :form :clojure.core.specs/binding-form))),
>
> the predicate that is actually failing in the spec, probably not
> particularly helpful given the complexity (and recursiveness) of the
> destructuring specs
>
>
> Extra input
>
> this is the part of cat that I think could be made more explicit - could
> be saying here that the value it had (above) was expected to match the next
> part of the cat (binding-form). So that could say the equivalent of
> "Expected binding-form but had non-matching value ..." and could even find
> what parts of that value matched and maybe which didn't (the :or keys) such
> that you'd have a more precise description. There is some more stuff Rich
> and I have worked on around "hybrid maps" which is the case here with map
> destructuring - it's particularly challenging to get a good error out of
> that at the moment, but there's more that can be done.
>
>
Thank you for doing the walkthrough. I observed this too and became
sceptical why spec doesn't go further down the path and apparently stops at
::binding-form.
I could isolate the problem a bit by changing the spec of ::arg-list and
temporarily removing the :varargs branch.
(s/def ::arg-list
(s/and
vector?
(s/cat :args (s/* ::binding-form)
;; :varargs (s/? (s/cat :amp #{'&} :form ::binding-form))
)))
This leads to a much better message:
(s/explain (:args (s/get-spec 'clojure.core/defn))
'[foo [{:or {a/b 42}}]])
In: [1 0] val: {:or #:a{b 42}} fails spec: :clojure.core.specs/local-name
at: [:bs :arity-1 :args :args :sym] predicate: simple-symbol?
In: [1 0 0] val: ([:or #:a{b 42}]) fails spec:
:clojure.core.specs/seq-binding-form at: [:bs :arity-1 :args :args :seq]
predicate: (cat :elems (* :clojure.core.specs/binding-form) :rest (? (cat
:amp #{(quote &)} :form :clojure.core.specs/binding-form)) :as (? (cat :as
#{:as} :sym :clojure.core.specs/local-name))), Extra input
In: [1 0 :or a/b 0] val: a/b fails spec: :clojure.core.specs/or at: [:bs
:arity-1 :args :args :map :or 0] predicate: simple-symbol?
In: [1 0] val: {:or #:a{b 42}} fails spec: :clojure.core.specs/arg-list at:
[:bs :arity-n :bodies :args] predicate: vector?
The third one is the desired one and very precise - it seems to be usually
the one with the largest :in path. The length of the :in path seems a good
sorting criterium for reporting.
However I was not able to track the issue further down. I also wasn't able
to reproduce a more minimal case of this problem. It seems like a bug in
how spec parses and must have something to do with s/cat and the :varargs
branch.
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