feat: treat selectors with leading '(//' as xpath (#821)

This starts treating the following selectors as xpath:
- `page.$('//div')`
- `page.$('(//div)[1]')`
- `page.$('((((//div))))[1]')`

(and generally, any number of leading openting parenthesis)

Fixes #817

Author: aslushnikov

src/dom.ts

@@ -511,7 +511,9 @@ function normalizeSelector(selector: string): string {
   const eqIndex = selector.indexOf('=');
   if (eqIndex !== -1 && selector.substring(0, eqIndex).trim().match(/^[a-zA-Z_0-9-]+$/))
     return selector;
-  if (selector.startsWith('//'))
+  // If selector starts with '//' or '//' prefixed with multiple opening
+  // parenthesis, consider xpath. @see https://github.com/microsoft/playwright/issues/817
+  if (/^\(*\/\//.test(selector))
     return 'xpath=' + selector;
   if (selector.startsWith('"'))
     return 'text=' + selector;

test/queryselector.spec.js

@@ -177,6 +177,11 @@ module.exports.describe = function({testRunner, expect, selectors, FFOX, CHROMIU
       const element = await page.$('//html/body/section');
       expect(element).toBeTruthy();
     });
+    it('should auto-detect xpath selector with starting parenthesis', async({page, server}) => {
+      await page.setContent('<section>test</section>');
+      const element = await page.$('(//section)[1]');
+      expect(element).toBeTruthy();
+    });
     it('should auto-detect text selector', async({page, server}) => {
       await page.setContent('<section>test</section>');
       const element = await page.$('"test"');