Fix cloud URL when Manage Jenkins UI is deferred

[ollehu]

Fixes #26106

In the new experimental deferred render, getNearestAncestorUrl returns null and sends the user to an invalid URL. Use request.getContextPath to build the cloud URL in that case.

Testing done

Let me know if any UTE is desired/required here. Unsure what goes for these experimental features. I did test that the URL builds correctly with this change.

Proposed changelog entries

• Fix cloud URL when using experimental settings redesign

Proposed changelog category

/label bug
/remove-label regression-fix

Proposed upgrade guidelines

N/A

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[timja]

Thanks for the PR / issue, cc @janfaracik, we'll need to dig into and see why its returning null and causing issues now.

[ollehu]

Thanks for the PR / issue, cc @janfaracik, we'll need to dig into and see why its returning null and causing issues now.

No problem. Long time Jenkins user, happy to contribute.

I traced the regression to the lazy loading introduced here: https://github.com/janfaracik/jenkins/blob/366b31bf16ec6c48e9e03e6c55cac39767b5b9e4/core/src/main/resources/lib/layout/settings-subpage.jelly#L120
With the lazy-loaded subpage, jenkins isn’t in the ancestor chain when the URL is constructed, so the base URL resolves to null. But I’m not a Java expert, and even less familiar with Apache Jelly.

[mawinter69]

Please also see #26002 (comment). Can you test if that is sufficient?

[ollehu]

Please also see #26002 (comment). Can you test if that is sufficient?

@mawinter69 Yes, setting noDefer="true" also solves this. Would you prefer that over safeguarding the URL-builder function?

[timja]

Please also see #26002 (comment). Can you test if that is sufficient?

@mawinter69 Yes, setting noDefer="true" also solves this. Would you prefer that over safeguarding the URL-builder function?

Yes please

[timja]

Thanks!

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