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PR preview pages don't handle visit to non deployed pages well #76
Description
Summary
Previews generated by the PR review companion include only the modified files. On preview pages, links to other unmodified pages give a 404 error. Also, the error is wrong: Key: pr37670/en-us/_spas/404.html. Following is the content of the 404 response:
404 Not Found
Code: NoSuchKey
Message: The specified key does not exist.
Key: pr37670/en-us/_spas/404.html
RequestId: W9ZG8PFR8V5N0MK5
HostId: EoaAHM8g7wgSv7rGa1dRb6/F9o5Pg93I6h0iZVYuA8A5x1RrlpNKgHZVADEZDyl/ZnC2KuEdIr8=
Reviewers find it annoying to see the 404 page instead of the requested page, even though it's not modified in the PR. It would be better if, on the 404 page, there is a link to the page on the production site.
Steps to reproduce
- Open any latest PR in the
mdn/contentrepo. - Open any preview page.
- On the page, click on any link to an MDN page that is not modified in the PR.
- You'll get
pr37670/en-us/_spas/404.htmlnot found error.
Solution
The solution is based on the TamporMonkey script created by Will. The script adds a link to the same doc on the production site. Instead of TamporMonkey, we can do it in the deployer code itself.\
During dev deployments for PRs, populate the /en-us/_spas/404.html file with the following content:
<!DOCTYPE html>
<HTML>
<head>
<title>404 Page Not Found</title>
</head>
<body>
<h1>404 Page Not Found</h1>
<script>
if (document.location.hostname.endsWith("content.dev.mdn.mozit.cloud")) {
const link = document.createElement("a");
link.href = `https://developer.mozilla.org${document.location.pathname}`;
link.textContent = "View on MDN production server.";
document.body.appendChild(link);
}
</script>
</body>
</html>Note: Ignore the fact that PR build doesn't populate the original _spas/404.html. The production style 404 page is not useful in PR previews anyway.
Activity
caugner commentedon Jan 23, 2025
The root cause for the missing 404 page is that it was moved from
/{locale}/_spas/404.htmlto/{locale}/404/index.htmlin mdn/yari#12248, while CloudFront was still configured to serve it from/en-US/_spas/404.html.I have now updated the CloudFront config to serve the correct error page.
OnkarRuikar commentedon Mar 15, 2025
I think this is still in progress. Convesation from the last meeting:
Josh-Cena commentedon Mar 15, 2025
I thought this issue is only about the bad not found page. If you think we should solve the whole 404 UX in this PR, that's fine to me. I'm not sure what the preferences are from the notes though. It seems people are neither happy with showing a 404 (current behavior) nor with directly redirecting to prod (previous behavior, iirc). Maybe a custom 404? But anyway this seems entirely out of control for the content repo and should go to engineering instead.
OnkarRuikar commentedon Mar 16, 2025
Move this issue to the rari repo?
I think they simply need to add a
View on MDN live serverlink to the current 404 page when it's not a prod environment.pepelsbey commentedon Mar 17, 2025
@caugner moved it to rari as it seemed like a proper place
caugner commentedon Mar 17, 2025
@pepelsbey Both the 404 page and the Cloud Function serving the 404 page are in yari.