fix RegExp sticky polyfill with alternation

Author: zloirock

CHANGELOG.md

@@ -31,6 +31,7 @@
 - Fixed named backreferences in `RegExp` NCG polyfill
 - Fixed some cases of `RegExp` NCG polyfill in combination with other types of groups
 - Fixed some cases of `RegExp` NCG polyfill in combination with `dotAll`
+- Fixed `RegExp` `sticky` polyfill with alternation
 - Fixed handling of some line terminators in case of `multiline` + `sticky` mode in `RegExp` polyfill
 - Fixed `.input` slicing on result object with `RegExp` `sticky` mode polyfill
 - Fixed handling of empty groups with `global` and `unicode` modes in polyfills

packages/core-js/internals/regexp-exec.js

@@ -79,7 +79,7 @@ if (PATCH) {
       var prevChar = re.lastIndex > 0 && charAt(str, re.lastIndex - 1);
       if (re.lastIndex > 0 &&
         (!re.multiline || re.multiline && prevChar !== '\n' && prevChar !== '\r' && prevChar !== '\u2028' && prevChar !== '\u2029')) {
-        source = '(?: ' + source + ')';
+        source = '(?: (?:' + source + '))';
         strCopy = ' ' + strCopy;
         charsAdded++;
       }

tests/unit-global/es.regexp.exec.js

@@ -94,4 +94,12 @@ if (DESCRIPTORS) {
     regex5.lastIndex = 2;
     assert.deepEqual(regex5.exec('.\u2029bar'), ['bar'], 'multiline sticky after \\u2029');
   });
+
+  QUnit.test('RegExp#exec sticky with alternation', assert => {
+    const re = new RegExp('a|b', 'y');
+    re.lastIndex = 1;
+    const result = re.exec('cb');
+    assert.deepEqual(result, ['b'], 'alternation matches non-first alternative at lastIndex');
+    assert.same(re.lastIndex, 2, 'lastIndex updated correctly');
+  });
 }