Drop support for `side-files`

[jglick]

While waiting a long time for a config page to load in a newly started controller, I decided to take a thread dump, and noticed this:

"Handling GET /mc/manage/configureClouds/ from … : Jetty (winstone)-… KubernetesCloud/DescriptorImpl/config.jelly PodTemplate/config.jelly" Id=… Group=main RUNNABLE
	at java.base@11.0.20/sun.nio.fs.UnixNativeDispatcher.lstat(UnixNativeDispatcher.java:334)
	at java.base@11.0.20/sun.nio.fs.UnixFileAttributes.get(UnixFileAttributes.java:72)
	at java.base@11.0.20/sun.nio.fs.UnixFileAttributeViews$Basic.readAttributes(UnixFileAttributeViews.java:52)
	at java.base@11.0.20/sun.nio.fs.UnixFileSystemProvider.readAttributes(UnixFileSystemProvider.java:149)
	at java.base@11.0.20/sun.nio.fs.LinuxFileSystemProvider.readAttributes(LinuxFileSystemProvider.java:99)
	at java.base@11.0.20/java.nio.file.Files.readAttributes(Files.java:1764)
	at java.base@11.0.20/java.nio.file.Files.isSymbolicLink(Files.java:2190)
	at org.eclipse.jetty.util.resource.PathResource.checkAliasPath(PathResource.java:98)
	at org.eclipse.jetty.util.resource.PathResource.<init>(PathResource.java:262)
	at org.eclipse.jetty.util.resource.PathResource.addPath(PathResource.java:367)
	at org.eclipse.jetty.server.handler.ContextHandler.getResource(ContextHandler.java:1947)
	at org.eclipse.jetty.webapp.WebAppContext.getResource(WebAppContext.java:410)
	at org.eclipse.jetty.webapp.WebAppContext$Context.getResource(WebAppContext.java:1444)
	at org.kohsuke.stapler.IndexHtmlDispatcher.make(IndexHtmlDispatcher.java:44)
	at org.kohsuke.stapler.MetaClass.buildDispatchers(MetaClass.java:153)
	at org.kohsuke.stapler.MetaClass.<init>(MetaClass.java:99)
	at org.kohsuke.stapler.WebApp$1.computeValue(WebApp.java:230)
	at org.kohsuke.stapler.WebApp$1.computeValue(WebApp.java:227)
	at java.base@11.0.20/java.lang.ClassValue.getFromHashMap(ClassValue.java:228)
	at java.base@11.0.20/java.lang.ClassValue.getFromBackup(ClassValue.java:210)
	at java.base@11.0.20/java.lang.ClassValue.get(ClassValue.java:116)
	at org.kohsuke.stapler.WebApp.getMetaClass(WebApp.java:246)
	at org.kohsuke.stapler.jelly.groovy.GroovyFacet.createRequestDispatcher(GroovyFacet.java:74)
	at org.kohsuke.stapler.RequestImpl.getView(RequestImpl.java:307)
	at org.kohsuke.stapler.RequestImpl.getView(RequestImpl.java:302)
	at hudson.model.Descriptor.getHelpFile(Descriptor.java:776)
	at hudson.model.Descriptor.getHelpFile(Descriptor.java:757)
	at hudson.model.Descriptor.getHelpFile(Descriptor.java:746)
	at …

Something spending time crawling the filesystem (not the jenkins.war) looking for something, but what?

stapler/core/src/main/java/org/kohsuke/stapler/IndexHtmlDispatcher.java

Line 10 in eca9c5f

* Serve {@code index.html} from {@code WEB-INF/side-files} if that exists.

but I have never heard of such a thing. History does not help much other than 95f7089 (#102)

Since this feature is rarely used…

In fact it seems this feature is never used at all. (Checked @cloudbees too.) Since we expect Stapler to only be used by Jenkins these days, we could simplify code and apparently speed up view initialization by dropping this feature.

[ahmed-kamal2004]

@timja @jglick
To address this issue effectively:

• Remove Support for side-files
  The side-files feature will be deprecated and removed from the Stapler project, as it has never been used. This streamlining will simplify the codebase and align with modern practices.

• Update Examples and Documentation
  All examples and documentation will be revised to reflect the updated approach, adhering to Jenkins Core's method of using Stapler. This ensures consistency and clarity for users.

If there's anything in this plan you believe needs further discussion, clarification, or adjustment, please let me know 🚀

[timja]

Sounds good it’s not infrequent use it’s never used outside of the stapler examples that we can tell