Fix noscript style evaluation during navigation (#1464)

[yujiteshima]

Pull Request

Title: Fix noscript style evaluation during navigation

Summary

Fixes #1464

This PR prevents Turbo from incorrectly evaluating <style> tags nested within <noscript> elements during page navigation.

Problem

Turbo's page rendering mechanism was evaluating content inside <noscript> elements, causing:

• Styles intended only for non-JavaScript environments to be applied
• Content to become hidden when display: none styles were applied during navigation

Solution

The fix deactivates <noscript> elements by converting their innerHTML to textContent in two critical places:

1. PageRenderer (page_renderer.js): Before adopting the new body element
2. PageSnapshot (page_snapshot.js): When creating cached snapshots

This conversion prevents browsers from parsing nested HTML/CSS while preserving the content as plain text.

Testing

Added a new test case that verifies styles inside <noscript> elements are not evaluated during Turbo navigation.

Reproduction Projects

• Unfixed version: https://github.com/yujiteshima/hotwire-turbo-issue-1464-repro
• Fixed version: https://github.com/yujiteshima/hotwire-turbo-issue-1464-repro-fix

[yujiteshima]

Note on CI Failure

The CI failure appears to be from a pre-existing flaky test, not related to this PR's changes.

The flaky test: navigation_tests.js:451 - "does not fire turbo:load twice after following a redirect"

I tested this on upstream/main (before my changes) and got the same intermittent failures - it passes about 80% of the time. The test added in this PR for the noscript fix passes consistently (5/5 runs).

The noscript fix itself is working correctly and the new test coverage is stable. Happy to re-run CI or provide more details if needed!

[packagethief]

Thanks @yujiteshima. This looks good. Just one (possibly silly) question. If turbo is controlling navigation we know that JavaScript is enabled, so any <noscript> element is irrelevant anyway. Instead of converting the element contents to text, could we just remove the element?

removeNoscriptElements() {
  for (const noscriptElement of this.newElement.querySelectorAll("noscript")) {
    noscriptElement.remove()
  }
}

[yujiteshima]

@packagethief Thank you for the suggestion—not silly at all! I agree that removing <noscript> elements is a better approach.

Since Turbo is running, JavaScript is demonstrably enabled, making <noscript> elements unnecessary. There's no practical reason for code to depend on <noscript> elements in a JavaScript-enabled environment, so removing them keeps the DOM cleaner and aligns better with Turbo's philosophy of progressive enhancement.

I'll update the implementation to use removeNoscriptElements() instead of deactivateNoscriptElements().

[yujiteshima]

@packagethief Updated! The implementation now removes <noscript> elements entirely using removeNoscriptElements().

The removal happens after document.adoptNode() to ensure consistent behavior across browsers—Firefox requires the element to be adopted into the current document before removal to prevent unintended style evaluation.

All tests are passing on both Chrome and Firefox.