Fix metosin#427

Comparing `-coll-gen` and `-coll-gen-distict` in the `malli.generator`
namespace, it seems there was no reason for the latter to handle
recursive generation any different. Both implementations now create a
generator based on the same initial conditions.

src/malli/generator.cljc

@@ -50,7 +50,7 @@
   (let [{:keys [min max]} (-min-max schema options)
         [continue options] (-recur schema options)
         child (-> schema m/children first)
-        gen (if continue (generator child options))]
+        gen (when continue (generator child options))]
     (gen/fmap f (cond
                   (not gen) (gen/vector gen/any 0 0)
                   (and min (= min max)) (gen/vector gen min)
@@ -63,8 +63,7 @@
   (let [{:keys [min max]} (-min-max schema options)
         [continue options] (-recur schema options)
         child (-> schema m/children first)
-        gen (if-not (and (= :ref (m/type child)) continue (<= (or min 0) 0))
-              (generator child options))]
+        gen (when continue (generator child options))]
     (gen/fmap f (if gen
                   (gen/vector-distinct gen {:min-elements min, :max-elements max, :max-tries 100})
                   (gen/vector gen/any 0 0)))))

test/malli/generator_test.cljc

@@ -267,3 +267,10 @@
                 ::E]
         valid? (m/validator schema)]
     (is (every? valid? (mg/sample schema {:size 10000})))))
+
+(deftest recursive-distinct-col-test
+  (is (not (every? empty?
+                   (mg/sample [:set
+                               {:registry {::foo :int}}
+                               [:ref ::foo]]
+                              {:size 1000})))))