Restore unsaved changes warning in new Manage Jenkins UI

[Maanvi212006]

Fixes #JENKINS-26270

Testing done

• Enabled the new Manage Jenkins UI
• Navigated to Manage Jenkins → System
• Modified a configuration value (for example, toggled a checkbox)
• Attempted to navigate away from the page or reload
• Verified that the browser displayed a native unsaved changes warning dialog
• Repeated the same steps on Security and Appearance pages

This change was tested manually since it affects frontend behavior.

Screenshots (UI changes only)

Before

No warning and one leaves the page potentially losing unsaved changes

After

Proposed changelog entries

• Restore unsaved changes warning on Manage Jenkins configuration pages

Proposed changelog category

/label bug,web-ui

Proposed upgrade guidelines

N/A

Submitter checklist

• The issue, if it exists, is well-described.
• The changelog entries and upgrade guidelines are appropriate for the audience affected by the change and are in the imperative mood.
• There is automated testing or an explanation as to why this change has no tests.
• New public classes, fields, and methods are annotated with @Restricted or have @since TODO Javadocs, as appropriate.
• New deprecations are annotated with @Deprecated(since = "TODO") or @Deprecated(forRemoval = true, since = "TODO"), if applicable.
• UI changes do not introduce regressions when enforcing the current default rules of the Content Security Policy Plugin.
• For dependency updates, there are links to external changelogs and, if possible, full differentials.
• For new APIs and extension points, there is a link to at least one consumer.

Desired reviewers

@jenkinsci/core-pr-reviewers

[MarkEWaite]

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[timja]

Please use the actual template not one you've made up:
https://raw.githubusercontent.com/jenkinsci/jenkins/refs/heads/master/.github/PULL_REQUEST_TEMPLATE.md

The change itself looks sensible, (assuming it works)

[MarkEWaite]

When I run Jenkins from this pull request with the command:

JENKINS_HOME=work java -jar war/target/jenkins.war

and complete the setup wizard by choosing to install no plugins, when I open the "Manage Jenkins" -> "System" page, it reports the following stack trace to the console:

2026-02-12 13:30:40.281+0000 [id=126]   INFO    h.m.UpdateCenter$CompleteBatchJob#run: Completed installation of 0 plugins in 17 ms
2026-02-12 13:30:56.201+0000 [id=32]    WARNING o.k.s.f.adjunct.AdjunctsInPage#findNeeded: No such adjunct found: hudson-behavior
org.kohsuke.stapler.framework.adjunct.NoSuchAdjunctException: Neither hudson-behavior.css, .js, .html, nor .jelly were found
        at org.kohsuke.stapler.framework.adjunct.Adjunct.<init>(Adjunct.java:127)
        at org.kohsuke.stapler.framework.adjunct.AdjunctManager.get(AdjunctManager.java:154)
        at org.kohsuke.stapler.framework.adjunct.AdjunctsInPage.findNeeded(AdjunctsInPage.java:169)
        at org.kohsuke.stapler.framework.adjunct.AdjunctsInPage.generate(AdjunctsInPage.java:115)
        at org.kohsuke.stapler.jelly.AdjunctTag.doTag(AdjunctTag.java:86)
        at org.apache.commons.jelly.impl.TagScript.run(TagScript.java:271)
        at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
        at org.kohsuke.stapler.jelly.CallTagLibScript$1.run(CallTagLibScript.java:100)
        at org.apache.commons.jelly.tags.define.InvokeBodyTag.doTag(InvokeBodyTag.java:91)
        at org.apache.commons.jelly.impl.TagScript.run(TagScript.java:271)
        at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
        at org.apache.commons.jelly.impl.TagScript.getBodyText(TagScript.java:767)
        at org.apache.commons.jelly.tags.core.CoreTagLibrary$3.run(CoreTagLibrary.java:141)
        at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
        at org.kohsuke.stapler.jelly.ReallyStaticTagLibrary$1.run(ReallyStaticTagLibrary.java:102)
        at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
        at org.kohsuke.stapler.jelly.ReallyStaticTagLibrary$1.run(ReallyStaticTagLibrary.java:102)
        at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
        at org.kohsuke.stapler.jelly.CallTagLibScript$1.run(CallTagLibScript.java:100)
        at org.apache.commons.jelly.tags.define.InvokeBodyTag.doTag(InvokeBodyTag.java:91)
        at org.apache.commons.jelly.impl.TagScript.run(TagScript.java:271)
        at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
        at org.apache.commons.jelly.tags.core.CoreTagLibrary$2.run(CoreTagLibrary.java:105)
        at org.kohsuke.stapler.jelly.CallTagLibScript.run(CallTagLibScript.java:121)
        at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
        at org.apache.commons.jelly.tags.core.CoreTagLibrary$2.run(CoreTagLibrary.java:105)
        at org.kohsuke.stapler.jelly.CallTagLibScript.run(CallTagLibScript.java:121)
        at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
        at org.apache.commons.jelly.tags.core.CoreTagLibrary$2.run(CoreTagLibrary.java:105)
        at org.kohsuke.stapler.jelly.CallTagLibScript.run(CallTagLibScript.java:121)
        at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
        at org.apache.commons.jelly.tags.core.CoreTagLibrary$2.run(CoreTagLibrary.java:105)

That will need to be fixed before the pull request can be merged.

[timja]

Also the screenshot doesn't have the feature flag enabled either.

So it doesn't show this fixed

Go to your profile in the top right, then experiments

Enable:

[mawinter69]

The hudson-behavior.js is always included and even when not that would not be the correct way.

[mawinter69]

I don't see why this should solve the problem. To detect that there is a changed field there is lib.form.confirm.js. I think it is loaded but for some reason it doesn't catch the changes.

[mawinter69]

With #26314 we have a much more promising approach.

[mawinter69]

/label proposed-for-close

[MarkEWaite]

Closing