Clojure

[spec] coll-of :min-count and :gen-max used together cause collections that are too large to be generated

Details

  • Type: Defect Defect
  • Status: Open Open
  • Priority: Minor Minor
  • Resolution: Unresolved
  • Affects Version/s: Release 1.9
  • Fix Version/s: Release 1.10
  • Component/s: None
  • Labels:
  • Environment:
    1.9.0-alpha16
  • Patch:
    Code
  • Approval:
    Vetted

Description

This should specify a spec whose generator always returns collections of size 4 or 5 but instead it generates collections of size 4 to 8:

(require '[clojure.spec.alpha :as s] '[clojure.spec.gen.alpha :as gen])
(map count (gen/sample (s/gen (s/coll-of char? :min-count 4 :gen-max 5))))
;; (4 7 8 8 4 7 4 5 5 7)

Cause: The max logic in s/every-impl is: (c/or max-count (max gen-max (c/* 2 (c/or min-count 0)))). If there is a max-count it's used, otherwise the larger of gen-max or 2*min-count is used. In this case, 2*min-count is 8. Seems like we should never generate more than gen-max though, so propose changing this logic to: (c/or max-count gen-max (c/* 2 (c/or min-count 0))).

Patch: clj-2202.patch

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  • Created:
    Updated: