fix some cases of serialization in URL polyfill

Author: zloirock

CHANGELOG.md

@@ -24,6 +24,7 @@
 - Fixed some percent encode cases / character sets in the `URL` polyfill
 - Fixed host parsing with `hostname = host:port` in the `URL` polyfill
 - Fixed invalid code points handling in UTF-8 decode in the `URLSearchParams` polyfill
+- Fixed some cases of serialization in `URL` polyfill ([step 3](https://url.spec.whatwg.org/#url-serializing))
 - Fixed `URL` polyfill `.origin` getter with `blob` scheme
 - Fixed a lack of error in `URLSearchParams.prototype.set` polyfill on calling only with 1 argument
 - Fixed handling invalid UTF-8 continuation bytes in `URLSearchParams` polyfill

packages/core-js/modules/web.url.constructor.js

@@ -814,6 +814,7 @@ URLState.prototype = {
       output += serializeHost(host);
       if (port !== null) output += ':' + port;
     } else if (scheme === 'file') output += '//';
+    if (host === null && !url.cannotBeABaseURL && path.length > 1 && path[0] === '') output += '/.';
     output += url.cannotBeABaseURL ? path[0] : path.length ? '/' + join(path, '/') : '';
     if (query !== null) output += '?' + query;
     if (fragment !== null) output += '#' + fragment;

tests/unit-global/web.url.js

@@ -139,6 +139,12 @@ QUnit.test('URL#href', assert => {
     // assert.throws(() => new URL('http://zloirock.ru/').href = 'http://a%b', 'forbidden host code point'); // no error in Chrome and FF
     // assert.throws(() => new URL('http://zloirock.ru/').href = '1http://zloirock.ru', 'incorrect scheme'); // no error in Chrome
   }
+
+  // URL serializing step 3 - /. prefix for non-special URLs with null host and path starting with empty segment
+  assert.same(new URL('x:/a/..//b').href, 'x:/.//b', '/. prefix prevents ambiguous serialization');
+  assert.same(new URL('x:/a/..//b').pathname, '//b', 'pathname is not affected by /. prefix');
+  assert.same(new URL('x:/.//b').href, 'x:/.//b', '/. prefix is idempotent');
+  assert.same(new URL(new URL('x:/a/..//b').href).pathname, '//b', '/. prefix round-trips correctly');
 });
 
 QUnit.test('URL#origin', assert => {

tests/unit-pure/web.url.js

@@ -140,6 +140,12 @@ QUnit.test('URL#href', assert => {
     // assert.throws(() => new URL('http://zloirock.ru/').href = 'http://a%b', 'forbidden host code point'); // no error in Chrome and FF
     // assert.throws(() => new URL('http://zloirock.ru/').href = '1http://zloirock.ru', 'incorrect scheme'); // no error in Chrome
   }
+
+  // URL serializing step 3 - /. prefix for non-special URLs with null host and path starting with empty segment
+  assert.same(new URL('x:/a/..//b').href, 'x:/.//b', '/. prefix prevents ambiguous serialization');
+  assert.same(new URL('x:/a/..//b').pathname, '//b', 'pathname is not affected by /. prefix');
+  assert.same(new URL('x:/.//b').href, 'x:/.//b', '/. prefix is idempotent');
+  assert.same(new URL(new URL('x:/a/..//b').href).pathname, '//b', '/. prefix round-trips correctly');
 });
 
 QUnit.test('URL#origin', assert => {