ensure result order in Set#intersection

packages/core-js-pure/override/internals/set-helpers.js

@@ -4,6 +4,7 @@ var tryToString = require('../internals/try-to-string');
 var iterateSimple = require('../internals/iterate-simple');
 
 var Set = getBuiltIn('Set');
+var SetPrototype = Set.prototype;
 var $TypeError = TypeError;
 
 var aSet = function (it) {
@@ -54,5 +55,7 @@ module.exports = {
   has: has,
   size: size,
   clone: clone,
-  iterate: iterate
+  iterate: iterate,
+  $has: SetPrototype.has,
+  $keys: SetPrototype.keys
 };

packages/core-js/internals/set-helpers.js

@@ -5,10 +5,12 @@ var iterateSimple = require('../internals/iterate-simple');
 // eslint-disable-next-line es/no-set -- safe
 var $Set = Set;
 var SetPrototype = $Set.prototype;
+var $has = SetPrototype.has;
+var $keys = SetPrototype.keys;
 var add = uncurryThis(SetPrototype.add);
 var forEach = uncurryThis(SetPrototype.forEach);
-var has = uncurryThis(SetPrototype.has);
-var keys = uncurryThis(SetPrototype.keys);
+var has = uncurryThis($has);
+var keys = uncurryThis($keys);
 var next = keys(new $Set()).next;
 
 var aSet = function (it) {
@@ -42,5 +44,7 @@ module.exports = {
   has: has,
   size: size,
   clone: clone,
-  iterate: iterate
+  iterate: iterate,
+  $has: $has,
+  $keys: $keys
 };

packages/core-js/internals/set-intersection.js

@@ -9,18 +9,38 @@ var add = SetHelpers.add;
 var has = SetHelpers.has;
 var size = SetHelpers.size;
 var forEach = SetHelpers.forEach;
+var nativeHas = SetHelpers.$has;
+var nativeKeys = SetHelpers.$keys;
+
+var isNativeSetRecord = function (record) {
+  return record.has === nativeHas && record.keys === nativeKeys;
+};
 
 // `Set.prototype.intersection` method
 // https://github.com/tc39/proposal-set-methods
 module.exports = function intersection(other) {
   var O = aSet(this);
   var otherRec = getSetRecord(other);
   var result = new Set();
-  if (size(O) <= otherRec.size) forEach(O, function (e) {
-    if (otherRec.includes(e)) add(result, e);
-  });
-  else iterateSimple(otherRec.getIterator(), function (e) {
-    if (has(O, e)) add(result, e);
-  });
+
+  // observable side effects
+  if (!isNativeSetRecord(otherRec) && size(O) > otherRec.size) {
+    iterateSimple(otherRec.getIterator(), function (e) {
+      if (has(O, e)) add(result, e);
+    });
+
+    if (size(result) < 2) return result;
+
+    var disordered = result;
+    result = new Set();
+    forEach(O, function (e) {
+      if (has(disordered, e)) add(result, e);
+    });
+  } else {
+    forEach(O, function (e) {
+      if (otherRec.includes(e)) add(result, e);
+    });
+  }
+
   return result;
 };

tests/unit-global/esnext.set.intersection.js

@@ -18,6 +18,13 @@ QUnit.test('Set#intersection', assert => {
   assert.deepEqual(from(new Set([1, 2, 3]).intersection(createSetLike([4, 5]))), []);
   assert.deepEqual(from(new Set([1, 2, 3]).intersection(createSetLike([2, 3, 4]))), [2, 3]);
 
+  assert.deepEqual(from(new Set([1, 2, 3]).intersection(new Set([3, 2]))), [2, 3]);
+  assert.deepEqual(from(new Set([1, 2, 3]).intersection(new Set([3, 2, 1]))), [1, 2, 3]);
+  assert.deepEqual(from(new Set([1, 2, 3]).intersection(new Set([3, 2, 1, 0]))), [1, 2, 3]);
+  assert.deepEqual(from(new Set([1, 2, 3]).intersection(createSetLike([3, 2]))), [2, 3]);
+  assert.deepEqual(from(new Set([1, 2, 3]).intersection(createSetLike([3, 2, 1]))), [1, 2, 3]);
+  assert.deepEqual(from(new Set([1, 2, 3]).intersection(createSetLike([3, 2, 1, 0]))), [1, 2, 3]);
+
   // TODO: drop from core-js@4
   assert.deepEqual(from(new Set([1, 2, 3]).intersection([4, 5])), []);
   assert.deepEqual(from(new Set([1, 2, 3]).intersection([2, 3, 4])), [2, 3]);

tests/unit-pure/esnext.set.intersection.js

@@ -19,6 +19,13 @@ QUnit.test('Set#intersection', assert => {
   assert.deepEqual(from(new Set([1, 2, 3]).intersection(createSetLike([4, 5]))), []);
   assert.deepEqual(from(new Set([1, 2, 3]).intersection(createSetLike([2, 3, 4]))), [2, 3]);
 
+  assert.deepEqual(from(new Set([1, 2, 3]).intersection(new Set([3, 2]))), [2, 3]);
+  assert.deepEqual(from(new Set([1, 2, 3]).intersection(new Set([3, 2, 1]))), [1, 2, 3]);
+  assert.deepEqual(from(new Set([1, 2, 3]).intersection(new Set([3, 2, 1, 0]))), [1, 2, 3]);
+  assert.deepEqual(from(new Set([1, 2, 3]).intersection(createSetLike([3, 2]))), [2, 3]);
+  assert.deepEqual(from(new Set([1, 2, 3]).intersection(createSetLike([3, 2, 1]))), [1, 2, 3]);
+  assert.deepEqual(from(new Set([1, 2, 3]).intersection(createSetLike([3, 2, 1, 0]))), [1, 2, 3]);
+
   // TODO: drop from core-js@4
   assert.deepEqual(from(new Set([1, 2, 3]).intersection([4, 5])), []);
   assert.deepEqual(from(new Set([1, 2, 3]).intersection([2, 3, 4])), [2, 3]);