CLJS-3454: New set instances are created when redundant data is added

Author: quoll

src/main/cljs/cljs/core.cljs

@@ -9304,7 +9304,10 @@ reduces them without incurring seq initialization"
 
   ICollection
   (-conj [coll o]
-    (PersistentHashSet. meta (assoc hash-map o nil) nil))
+    (let [m (-assoc hash-map o nil)]
+      (if (identical? m hash-map)
+        coll
+        (PersistentHashSet. meta m nil))))
 
   IEmptyableCollection
   (-empty [coll] (-with-meta (.-EMPTY PersistentHashSet) meta))
@@ -9341,7 +9344,10 @@ reduces them without incurring seq initialization"
 
   ISet
   (-disjoin [coll v]
-    (PersistentHashSet. meta (-dissoc hash-map v) nil))
+    (let [m (-dissoc hash-map v)]
+      (if (identical? m hash-map)
+        coll
+        (PersistentHashSet. meta m nil))))
 
   IFn
   (-invoke [coll k]
@@ -9459,7 +9465,10 @@ reduces them without incurring seq initialization"
 
   ICollection
   (-conj [coll o]
-    (PersistentTreeSet. meta (assoc tree-map o nil) nil))
+    (let [m (-assoc tree-map o nil)]
+      (if (identical? m tree-map)
+        coll
+        (PersistentTreeSet. meta m nil))))
 
   IEmptyableCollection
   (-empty [coll] (PersistentTreeSet. meta (-empty tree-map) 0))
@@ -9513,7 +9522,10 @@ reduces them without incurring seq initialization"
 
   ISet
   (-disjoin [coll v]
-    (PersistentTreeSet. meta (dissoc tree-map v) nil))
+    (let [m (-dissoc tree-map v)]
+      (if (identical? m tree-map)
+        coll
+        (PersistentTreeSet. meta m nil))))
 
   IFn
   (-invoke [coll k]

src/test/cljs/cljs/core_test.cljs

@@ -737,6 +737,27 @@
   (is (= #{1 2} (hash-set 1 2 2)))
   (is (= #{1 2} (apply hash-set [1 2 2]))))
 
+(deftest test-ordered-set
+  (is (= #{1 2} (sorted-set 1 2 2)))
+  (is (= [1 2 3] (seq (sorted-set 2 3 1))))
+  (is (= #{1 2} (apply sorted-set [1 2 2]))))
+
+(deftest test-3454-conj
+  (is (= #{1 2 3} (conj #{1 2} 3)))
+  (is (= #{1 2 3} (conj (sorted-set 1 2) 3)))
+  (let [s #{1 2}
+        ss (sorted-set 1 2)]
+    (is (identical? s (conj s 2)))
+    (is (identical? ss (conj ss 2)))))
+
+(deftest test-3454-disj
+  (is (= #{1 2} (disj #{1 2 3} 3)))
+  (is (= #{1 2} (disj (sorted-set 1 2 3) 3)))
+  (let [s #{1 2}
+        ss (sorted-set 1 2)]
+    (is (identical? s (disj s 3)))
+    (is (identical? ss (disj ss 3)))))
+
 (deftest test-585
   (is (= (last (map identity (into [] (range 32)))) 31))
   (is (= (into #{} (range 32))