fix: show correct error message. (#21388)

Co-authored-by: Rachel <rachel@cypress.io>

Author: sainthkh

packages/driver/cypress/integration/commands/querying/querying_spec.js

@@ -1230,6 +1230,16 @@ describe('src/cy/commands/querying', () => {
       cy.get('#backslashes').contains('"<OE_D]dQ\\')
     })
 
+    // https://github.com/cypress-io/cypress/issues/21108
+    it('shows correct error message when regex starts with =(equals sign)', () => {
+      cy.on('fail', (err) => {
+        expect(err.message).to.include('Expected to find content')
+      })
+
+      cy.visit('fixtures/dom.html')
+      cy.contains(/=[0-6]/, { timeout: 100 }).should('have.text', 'a=2')
+    })
+
     describe('should(\'not.exist\')', () => {
       it('returns null when no content exists', () => {
         cy.contains('alksjdflkasjdflkajsdf').should('not.exist').then(($el) => {

packages/driver/src/config/jquery.ts

@@ -51,6 +51,14 @@ $.find.matchesSelector = function (elem, expr) {
       return matchesSelector.apply(_this, args)
     },
     catchFn (e) {
+      // https://github.com/cypress-io/cypress/issues/21108
+      // When regex starts with =, it is a syntax error when nothing found.
+      // Because Sizzle internally escapes = to handle attribute selectors.
+      // @see https://github.com/jquery/sizzle/blob/20390f05731af380833b5aa805db97de0b91268a/external/jquery/jquery.js#L4363-L4370
+      if (e.message.includes(`Syntax error, unrecognized expression: :cy-contains('`)) {
+        return false
+      }
+
       throw e
     },
     finallyFn () {