fix cloning of regex through RegExp constructor, close #948

CHANGELOG.md

@@ -1,6 +1,6 @@
 ## Changelog
 ##### Unreleased
-- Nothing
+- Fixed cloning of regex through `RegExp` constructor, [#948](https://github.com/zloirock/core-js/issues/948)
 
 ##### 3.15.0 - 2021.06.21
 - Added `RegExp` named capture groups polyfill, [#521](https://github.com/zloirock/core-js/issues/521), [#944](https://github.com/zloirock/core-js/issues/944)

packages/core-js/modules/es.regexp.constructor.js

@@ -113,17 +113,16 @@ if (isForced('RegExp', BASE_FORCED)) {
     var patternIsRegExp = isRegExp(pattern);
     var flagsAreUndefined = flags === undefined;
     var groups = [];
-    var rawPattern, rawFlags, dotAll, sticky, handled, result, state;
+    var rawPattern = pattern;
+    var rawFlags, dotAll, sticky, handled, result, state;
 
-    if (!thisIsRegExp && patternIsRegExp && pattern.constructor === RegExpWrapper && flagsAreUndefined) {
+    if (!thisIsRegExp && patternIsRegExp && flagsAreUndefined && pattern.constructor === RegExpWrapper) {
       return pattern;
     }
 
-    if (CORRECT_NEW) {
-      if (patternIsRegExp && !flagsAreUndefined) pattern = pattern.source;
-    } else if (pattern instanceof RegExpWrapper) {
-      if (flagsAreUndefined) flags = getFlags.call(pattern);
+    if (patternIsRegExp || pattern instanceof RegExpWrapper) {
       pattern = pattern.source;
+      if (flagsAreUndefined) flags = 'flags' in rawPattern ? rawPattern.flags : getFlags.call(rawPattern);
     }
 
     pattern = pattern === undefined ? '' : String(pattern);
@@ -148,11 +147,7 @@ if (isForced('RegExp', BASE_FORCED)) {
       groups = handled[1];
     }
 
-    result = inheritIfRequired(
-      CORRECT_NEW ? new NativeRegExp(pattern, flags) : NativeRegExp(pattern, flags),
-      thisIsRegExp ? this : RegExpPrototype,
-      RegExpWrapper
-    );
+    result = inheritIfRequired(NativeRegExp(pattern, flags), thisIsRegExp ? this : RegExpPrototype, RegExpWrapper);
 
     if (dotAll || sticky || groups.length) {
       state = enforceInternalState(result);

tests/tests/es.regexp.constructor.js

@@ -12,7 +12,7 @@ if (DESCRIPTORS) {
     assert.looksNative(RegExp);
     assert.ok({}.toString.call(RegExp()).slice(8, -1), 'RegExp');
     assert.ok({}.toString.call(new RegExp()).slice(8, -1), 'RegExp');
-    const regexp = /a/g;
+    let regexp = /a/g;
     assert.notStrictEqual(regexp, new RegExp(regexp), 'new RegExp(regexp) isnt regexp');
     assert.strictEqual(regexp, RegExp(regexp), 'RegExp(regexp) is regexp');
     regexp[Symbol.match] = false;
@@ -26,8 +26,17 @@ if (DESCRIPTORS) {
     assert.strictEqual(String(new RegExp(/a/g, 'mi')), '/a/im', 'Allows a regex with flags');
     assert.ok(new RegExp(/a/g, 'im') instanceof RegExp, 'Works with instanceof');
     assert.strictEqual(new RegExp(/a/g, 'im').constructor, RegExp, 'Has the right constructor');
+
+    const orig = /^https?:\/\//i;
+    // eslint-disable-next-line regexp/no-useless-assertions -- false positive
+    regexp = new RegExp(orig);
+    assert.ok(regexp !== orig, 'new + re + no flags #1');
+    assert.same(String(regexp), '/^https?:\\/\\//i', 'new + re + no flags #2');
+    let result = regexp.exec('http://github.com');
+    assert.deepEqual(result, ['http://'], 'new + re + no flags #3');
+
     /(b)(c)(d)(e)(f)(g)(h)(i)(j)(k)(l)(m)(n)(o)(p)/.exec('abcdefghijklmnopq');
-    let result = true;
+    result = true;
     const characters = 'bcdefghij';
     for (let i = 0, { length } = characters; i < length; ++i) {
       const chr = characters[i];