Close #453: best-effort ordered s/enum print via cached field

CHANGELOG.md

@@ -1,3 +1,6 @@
+## NEXT
+ * [#449](https://github.com/plumatic/schema/issues/453): Preserve `s/enum` order during printing
+
 ## 1.4.1 (`2022-09-29`)
  * [#449](https://github.com/plumatic/schema/issues/449): Fix bad jsdoc
 

src/cljc/schema/core.cljc

@@ -284,15 +284,21 @@
 
 ;;; enum (in a set of allowed values)
 
+(defn- best-effort-ordered-form [{:keys [vs] :as enum}]
+  (or (force (get (::form-hints enum) vs))
+      (cons 'enum vs)))
+
 (macros/defrecord-schema EnumSchema [vs]
   Schema
   (spec [this] (leaf/leaf-spec (spec/precondition this #(contains? vs %) #(list vs %))))
-  (explain [this] (cons 'enum vs)))
+  (explain [this] (best-effort-ordered-form this)))
 
 (clojure.core/defn enum
   "A value that must be = to some element of vs."
   [& vs]
-  (EnumSchema. (set vs)))
+  (let [svs (set vs)]
+    (-> (EnumSchema. svs)
+        (assoc ::form-hints {svs (delay (seq (into ['enum] (distinct) vs)))}))))
 
 
 ;;; pred (matches all values for which p? returns truthy)

test/cljc/schema/core_test.cljc

@@ -133,7 +133,26 @@
     (valid! schema 1)
     (invalid! schema :c)
     (invalid! (s/enum :a) 2 "(not (#{:a} 2))")
-    (is (= '(1 :a :b enum) (sort-by str (s/explain schema))))))
+    (is (= '(enum :a :b 1) (s/explain schema))))
+  (is (= (cons 'enum (range 1000)) (s/explain (apply s/enum (range 1000)))))
+  (testing "prints as if (distinct vs), which preserves original order"
+    (is (= '(enum 1 2 3 4) (s/explain (s/enum 1 2 1 3 1 4)))))
+  (testing "still prints correctly if implementation details are exploited"
+    (dotimes [_ 100]
+      (let [[a b c] (repeatedly #(rand-nth
+                                   [(gensym)
+                                    (str (gensym))
+                                    (keyword (gensym))]))
+            _ (assert (distinct? a b c))
+            e (s/enum a b)
+            _ (testing "prints in order"
+                (is (= (list 'enum a b) (s/explain e))))
+            e (update e :vs conj c)
+            _ (testing "adding an extra entry using implementation details just prints using the set's order"
+                (is (= (cons 'enum (:vs e)) (s/explain e))))
+            e (update e :vs disj c)
+            _ (testing "resetting :vs preserves the original printing order"
+                (is (= (list 'enum a b) (s/explain (update e :vs disj c)))))]))))
 
 (deftest pred-test
   (let [schema (s/pred odd? 'odd?)]