Require data to match coll type

[brjann]

It does not seem to be possible to require data to match the type of collection in a data spec.

For example both (s/valid? (ds/spec ::x #{int?}) [1 2 3]) and (s/valid? (ds/spec ::x [int?]) #{1 2 3}) return true. I have been bitten by this where I accidentally passed a list instead of a set to a function, which passed the spec check and since contains? accepts list, no error occured.

Is it possible to require an exact match on collection type?

[ikitommi]

sounds like a bug. PR welcome.

[brjann]

I wish I had enough Clojure / spec skills to submit a PR on this :-)

[brjann]

While
(s/valid? (ds/spec ::x {int? int?}) #{1 2}) returns false,
(s/valid? (ds/spec ::x {int? int?}) #{[1 2]}) returns true

So it seems that one must be able to convert the value to its correct form for the spec check to succeed

A call to s/conform seems to coerce the value to it's correct form
(s/conform (ds/spec ::x {int? #{int}}) [[1 [1 2 3]]])
=> {1 #{1 3 2}}

[wandersoncferreira]

@brjann there is some explanation in the mentioned PR above to fix the issue you reported.

[brjann]

@wandersoncferreira wow, thanks! Does this also make (s/valid? (ds/spec ::x {int? int?}) #{[1 2]}) return false?

[wandersoncferreira]

Unfortunately not @brjann , it seems related but it is not the same error. From some investigation, seems like the code performing the destructuring of #{[1 2]} is treating it the same way as #{1 2}. I am trying to look where this is done.

[wandersoncferreira]

Which is interesting is that (s/valid? (ds/spec ::x {int? int?}) #{[1 2 3]}) returns false as expected. This error is only happening with exact 2 elements inside the array.

[brjann]

I would guess that ´[k v]´ is identified as a key value pair. (s/valid? (ds/spec ::x {int? int?}) [[1 2] [2 1]]) is also valid, while (s/valid? (ds/spec ::x {int? int?}) [[1 2] [2 1 3]]) is not.
Also, (s/conform (ds/spec ::x {int? int?}) [[1 2] [2 1]]) => {1 2 2 1}

[wandersoncferreira]

Yes, I got the whole picture now.

When the map-of-spec is called to create our data spec, we rely on clojure.spec.alpha/every-impl to create it. However, this function has the following logic to perform the dispatch for each value when you ask to conform-all values in the map: https://github.com/clojure/spec.alpha/blob/master/src/main/clojure/clojure/spec/alpha.clj#L1298

And the problem lies in the (seq x) call. x is our data in this case #{[1 2 3 4]} . However, take a look at the destructuring below (simplified version of what the every-impl does):

;; the value of v
(let [x #{[1 2 3]}
      [v & vs :as vseq] (seq x)]
  v) ;; => [1 2 3]

;;; where v is used
(let [x #{[1 2 3]}
      [v & vs :as vseq] (seq x)]
  (conform* spec v))

And what is spec? Looking at impl/map-of-spec, spec is checking for a key-value tuple. And seq just got rid off our #{} literal. Then when the number of itens inside the vector is even, (conform* spec v) returns true and everything is fine.

Now, I'm not sure how can we approach to fix the issue. I looked under the hood of s/map-of which seems to do this just fine, however the implementation to some of the parts, e.g. cpred parameter, is a lot more complex than the current coll? call spec-tools is using right now.

EDIT:

Seems like changing cpred from coll? to map? fix this issue and does not produce any regression problem with the test suite. I will add this new commit to the open PR. (Y)

[brjann]

Thank you @wandersoncferreira !