fix: bug where cy.createSnapshot would interact with documents using custom elements

[panzarino]

• Closes Cypress getting into an infinite XHR request loop #1068
• Closes Cypress snapshotting causes attributeChangedCallback to be triggered on custom elements #7187

User facing changelog

• Fixes a bug where cy.createSnapshot would interact with documents using custom elements
  • Fixes an issue many users were having where Cypress would get stuck in an infinite XHR loop on documents that used custom elements

Additional details

See the following test case as reported in the issue

Before:

it('hangs', () => {
  cy.visit('https://evryplace.com/panel/');
})

In Cypress during cypress open

The cy.visit() does not resolve and the browser locks up in all browsers (Chrome, Electron) during cypress open. There are infinite requests that go out every second to GET /panel/i18n/7fa71d4/app-webvr_en.json.

In Cypress during cypress run

The behavior is actually different during cypress run. The cy.visit() resolves and the test passes (although it looks like the page doesn't load exactly right still).

After:

The page loads properly as expected

PR Tasks

• Have tests been added/updated?
• Has the original issue been tagged with a release in ZenHub?

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[cypress]

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Test summary

7912 • 0 • 130 • 2

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Run details

Project	cypress
Status	Passed
Commit	b67e291
Started	Jul 28, 2020 4:26 PM
Ended	Jul 28, 2020 4:33 PM
Duration	06:25 💡
OS	Linux Debian - 10.1
Browser	Multiple

View run in Cypress Dashboard ➡️

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[jennifer-shehane]

@panzarino So nice. I confirmed manually that this fixes the original bug.

This actually fixes this other issue also, where calling clone would trigger an attributeChangedCallback within the application. #7187 (comment) This case may be more testable - seems you could ensure this isn't called if snapshots are on. I wonder if it's the same reason that's causing the polymer issue?

@chrisbreiding may have some advice on writing a test case or assessing why this is happening.

[flotwig]

@chrisbreiding added you for review since this seems to be fixing a Shadow DOM-related issue, apparently unrelated to the new Shadow DOM changes

[flotwig]

@panzarino please add a test case here that demonstrates what is happening to shadow DOM elements on clone and that it is no longer happening

also, wow, shadow DOM? that was NOT my guess at all as to why this was happening 🤣