Issue with spec-ing higher-order functions; clojure.lang.AFunction$1 cannot be cast to clojure.lang.MultiFn

[Josip Gracin]

Hi!

The following test throws an exception when run using "lein test" and I can't figure out why.

(ns issue

  (:require  [clojure.test :as t]

             [clojure.spec.alpha :as s]

             [clojure.spec.test.alpha :as st]))

(s/fdef ::boolean-supplier

  :args (s/cat)

  :ret boolean?)

(defn make-fn [boolean-supplier]

  (fn []

    (boolean-supplier)))

(s/fdef make-fn

  :args (s/cat :supplier ::boolean-supplier))

(t/deftest issue

  (t/testing "issue demo"

    (st/instrument)

    (make-fn (fn [] true))))

Here's the output of "lein test":

$ lein test                       

                                                         

lein test issue                                                

                                                                  

lein test :only issue/issue                                                      

                                                           

ERROR in (issue) (Compiler.java:7647)                          

Uncaught exception, not in assertion.                                                  

expected: nil                                                                 

  actual: clojure.lang.Compiler$CompilerException: Syntax error compiling at (clojure/test/check/clojure_test.cljc:95:1).

#:clojure.error{:phase :compile-syntax-check, :line 95, :column 1, :source "clojure/test/check/clojure_test.cljc"}

 at clojure.lang.Compiler.load (Compiler.java:7647)                          

    clojure.lang.RT.loadResourceScript (RT.java:381)                 

    clojure.lang.RT.loadResourceScript (RT.java:372)                                            

    clojure.lang.RT.load (RT.java:463)                          

    clojure.lang.RT.load (RT.java:428)

    ...

Caused by: java.lang.ClassCastException: clojure.lang.AFunction$1 cannot be cast to clojure.lang.MultiFn

 at clojure.core$get_method.invokeStatic (core.clj:1817)

    clojure.core$get_method.invoke (core.clj:1817)                                     

    clojure.test.check.clojure_test$eval1131.invokeStatic (clojure_test.cljc:95)

    clojure.test.check.clojure_test$eval1131.invoke (clojure_test.cljc:95)

    clojure.lang.Compiler.eval (Compiler.java:7176)                          

    clojure.lang.Compiler.load (Compiler.java:7635)

    ...

Using Java 10.0.2 and the following dependencies:

$ lein deps :tree

 [clojure-complete "0.2.5" :exclusions [[org.clojure/clojure]]]

 [nrepl "0.5.3" :exclusions [[org.clojure/clojure]]]

   [nrepl/bencode "1.0.0"]

 [org.clojure/clojure "1.10.0"]

 [org.clojure/core.specs.alpha "0.2.44"]

 [org.clojure/spec.alpha "0.2.176"]

 [org.clojure/test.check "0.9.0"]

Any ideas?

[Alex Miller]

Your boolean-supplier should be:

(s/def ::boolean-supplier

  (s/fspec

    :args (s/cat)

    :ret boolean?))

[Josip Gracin]

Thanks!  I understand why my version is incorrect.  However, I get the same error with the corrected spec.

[Alex Miller]

The modified version works for me, so not sure what you're seeing.

$ clj

Clojure 1.10.0

user=> 

(ns issue

  (:require  [clojure.test :as t]

             [clojure.spec.alpha :as s]

             [clojure.spec.test.alpha :as st]))

nil

issue=> 

(s/def ::boolean-supplier

  (s/fspec

    :args (s/cat)

    :ret boolean?))

:issue/boolean-supplier

issue=>

(defn make-fn [boolean-supplier]

  (fn []

    (boolean-supplier)))

#'issue/make-fn

issue=>

(s/fdef make-fn

  :args (s/cat :supplier ::boolean-supplier))

issue/make-fn

issue=>

(t/deftest issue

  (t/testing "issue demo"

    (st/instrument)

    (make-fn (fn [] true))))

#'issue/issue

issue=> (issue)

nil

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[Josip Gracin]

Thanks! I've created an issue in Leiningen tracker
(https://github.com/technomancy/leiningen/issues/2524) because it
might have to do with it.