Actually I nearly forgot Oleg you were driving the Google summer of code
last year, what do you think?
On Tue 4 Jul 2017 at 17:44, Stephen Connolly <
stephen.alan.conno...@gmail.com> wrote:
> Ulli,
>
> What do you think on this proposal, given that you have contact with a lot
> of students who have been trying to get to grips with the Jenkins code base.
>
> Would it make their task easier?
>
> -Stephen
>
> On 3 July 2017 at 05:21, Stephen Connolly <stephen.alan.conno...@gmail.com
> > wrote:
>
>> I have been developing Jenkins plugins and changes to Jenkins core for
>> more than 10 years now. As such, I have internalized a lot of the knowledge
>> about how to develop against Jenkins and more specifically against Stapler.
>>
>> When I talk to people trying to start out development against Jenkins,
>> the magic of Stapler seems to be a big source of confusion - at least to
>> the people I have talked to.
>>
>> Prospective developers get confused:
>>
>> - between primary facets and facet fragments.
>> - where to put facets and facet fragments.
>> - which facet fragments are optional and which ones are mandatory
>>
>> (Did you even know that those jelly / groovy views are called facets and
>> that there are two kinds?)
>>
>> Some of those concerns affect me too... but I am a seasoned Jenkins
>> developer CMD+SHIFT+P, *, ENTER and IntelliJ is showing me a full list of
>> facets and facet fragments from the class hierarchy and I can search each
>> one looking for the <st:include page="fragment" optional="true"> to
>> discover that there is an optional facet fragment... and then try and dig
>> through the Jelly / Groovy logic to determine when and why that fragment
>> should be included.
>>
>> It doesn't just stop there... There are those methods that we expect
>> Stapler to invoke for us... typically they are the doFillXYZItems() or
>> doCheckXYZ() methods. I find myself having to mark them up like:
>>
>> @SuppressWarnings("unused") // stapler
>> public FormValidation doCheckWidgetValue(@QueryParameter String value) {
>> ...
>> }
>>
>>
>> So that my IDE stops complaining about the dead code. It's not a big deal
>> in the grand scheme of things, but I'd much rather have an annotation on
>> the method to signify that we expect the method to be used by stapler...
>> Right now I could do that using
>>
>> @WebMethod(name="checkWidgetValue")
>> public FormValidation doCheckWidgetValue(@QueryParameter String value) {
>> ...
>> }
>>
>>
>> If I don't like that, I guess I could use the newer HTTP verb annotations
>> in stapler:
>>
>> @GET // stapler
>> public FormValidation doCheckWidgetValue(@QueryParameter String value) {
>> ...
>> }
>>
>>
>> But the simple @GET is not screaming out stapler to me, so I feel
>> compelled to add a // stapler comment to remind myself that the
>> annotation is used by stapler
>>
>> Then we hit the actual name that stapler exposes things on. There are
>> some conventions that stapler follows... and they are magic conventions...
>> so much so that I just keep http://stapler.kohsuke.org/reference.html as
>> the first bookmark in my bookmark bar.
>>
>> I think we can do better. I think we should do better, and here is my
>> proposal.
>>
>> We should introduce some annotations. Make them available against older
>> versions of Jenkins so that we don't have to wait for everyone to update
>> their plugin baseline. The annotations can be added as a plugin dependency
>> in the parent pom, that everyone can use them just by upgrading the plugin
>> parent pom.
>>
>> Here are the class annotations I think we need:
>>
>> - An annotation (I propose @StaplerObject) that says "This object is
>> expected to bound to a URL by Stapler, the Stapler annotations are
>> complete, check that there are no facets / fragments without a
>> corresponding annotation and no magic on this class please" (so if there
>> is, say a rename.jelly but no @StaplerFacet("rename") or
>> @StaplerFragment("rename") then you get an error)
>> - An annotation (I propose @StaplerFacet and the repeatable container
>> @StaplerFacets) that says "Here are the facets that this object is
>> expected to have" (doesn't have to be on a @StaplerObject but when
>> not on a @StaplerObject we can only check for missing expected
>> facets, we cannot check for "unexpected" facets - i.e. I created a facet
>> with a spelling mistake or typo in the name)
>> - An annotation (I propose @StaplerFragment and the repeatable
>> container @StaplerFragments) that says "Here are the facet fragments
>> that this object is required or may optionally have" (quite often will not
>> be on a @StaplerObject)
>>
>>
>> So I envision something like this (pre-Java 8):
>>
>> @StaplerObject
>> @StaplerFacets({
>> @StaplerFacet("index"),
>> @StaplerFacet("config")
>> })
>> @StaplerFragments({
>> @StaplerFragment("main"),
>> @StaplerFragment("side-panel"),
>> @StaplerFragment(value="tasks",optional=true)
>> })
>> public class Widget { ... }
>>
>>
>> When compiled targeting Java 8 this would become:
>>
>> @StaplerObject
>> @StaplerFacet("index")
>> @StaplerFacet("config")
>> @StaplerFragment("main")
>> @StaplerFragment("side-panel")
>> @StaplerFragment(value="tasks",optional=true)
>> public class Widget { ... }
>>
>>
>> There would be an annotation processor that could do some checks:
>>
>> - If you add @StaplerFragment(..., optional=false) then any
>> non-abstract class must have that fragment somewhere in the class
>> hierarchy
>> - If you add @StaplerFacet then any non-abstract class must have that
>> fragment somewhere in the class hierarchy
>> - If you add @StaplerObject then only the named facets and facet
>> fragments must be present for that class (to catch somebody calling the
>> facet resource with an incorrect name - it should be side-panel2.jelly
>> but they called it sidepanel2.jelly)
>>
>>
>> Then, while we are at it, I'd also like to add method / field annotations:
>>
>> - An annotation (I propose @StaplerPath and the repeatable container
>> @StaplerPaths) that says "here is the URL segment names that this
>> method / field matches when Stapler is binding the URL". This annotation
>> can be used to enable easier refactoring without risk of breaking the URLs
>> because we can rename the getters and keep the URL scheme as before or
>> even
>> keep the legacy URLs but direct to the new URLs via the UI.
>> - Annotations (I propose @StaplerHEAD / @StaplerGET / @StaplerPOST /
>> @StaplerPUT / @StaplerPATCH / @StaplerDELETE plus non standard
>> methods supported with @StaplerMethod("...") and then a repeatable
>> container of @StaplerMethods - the repeatable container would only
>> take @StaplerMethod annotations though) that cover the different HTTP
>> methods (a.k.a. verbs) - we have some existing, but they need some
>> extensions and I think it might be a good idea to consolidate the names,
>> especially if we want to allow consumption on older baseline versions of
>> Jenkins
>>
>>
>> So this could be something like this (Pre Java 8):
>>
>> public class Widget {
>> @StaplerPath
>> public Manchu manchu;
>>
>> @StaplerPaths({@StaplerPath,@StaplerPath("fu")})
>> public Foo foo;
>>
>> @StaplerPath
>> public Bar getBar() { ... }
>>
>> @StaplerPath(StaplerPath.DYNAMIC)
>> public Object getDynamic(StaplerRequest req) { ... }
>>
>> @StaplerPOST
>> public HttpResponse doActivate(StaplerRequest req) { ... }
>>
>> @StaplerPath(StaplerPath.DYNAMIC)
>> @StaplerPUT
>> public HttpResponse doDynamic(StaplerRequest req) { ... }
>> }
>>
>>
>> Or targeting Java 8:
>>
>> public class Widget {
>> @StaplerPath
>> public Manchu manchu;
>>
>> @StaplerPath
>> @StaplerPath("fu")
>> public Foo foo;
>>
>> @StaplerPath
>> public Bar getBar() { ... }
>>
>> @StaplerPath(StaplerPath.DYNAMIC)
>> public Object getDynamic(StaplerRequest req) { ... }
>>
>> @StaplerPOST
>> public HttpResponse doActivate(StaplerRequest req) { ... }
>>
>> @StaplerPath(StaplerPath.DYNAMIC)
>> @StaplerPUT
>> public HttpResponse doDynamic(StaplerRequest req) { ... }
>> }
>>
>>
>> The annotation processor can then give additional checks:
>>
>>
>> - @StaplerPath annotated fields must be public
>> - @StaplerPath(altName) annotated fields are only allowed if
>> targeting a new version Stapler that adds support for that (unless the
>> name
>> is the inferred name)
>> - @StaplerPath annotated methods must be public and either match one
>> of the allowed getter signatures or also have a HTTP method annotation and
>> match the allowed action method signatures.
>> - @StaplerPath(altName) annotated methods are only allowed if
>> targeting a new version Stapler that adds support for that (unless the
>> name
>> is the inferred name)
>> - @StaplerHEAD / @StaplerGET / @StaplerPOST / @StaplerPUT /
>> @StaplerPATCH / @StaplerDELETE annotated methods must be public and
>> match one of the allowed action method signatures. The method name must
>> match the convention for action method inference (subject to
>> @WebMethod(name="...") overriding when *compiling against older
>> versions of Stapler* - but it would be an error to use @WebMethod if
>> compiling against newer versions of Stapler because we can move to the new
>> annotations in those cases)
>> - If the class is @StaplerObject annotated we can do additional
>> checks for overlapping facets, for example where an action method or a
>> getter will hide a facet (it's ok to hide the facet for non HEAD/GET
>> requests though)
>>
>> There are probably additional checks that we can add as we figure them
>> out.
>>
>>
>> Now there are some open questions:
>>
>> - Does it make sense to start all these annotations with Stapler? My
>> initial stab at this was to use @Staple in place of @StaplerPath and
>> to re-use the @GET / @POST / @PUT / @DELETE verbs but mandating the
>> @Staple annotation so that you would have:
>>
>> @Staple @POST
>>
>> public HttpResponse doActivate(StaplerRequest req) { ... }
>>
>>
>> rather than
>>
>> @StaplerPOST
>>
>> public HttpResponse doActivate(StaplerRequest req) { ... }
>>
>>
>> One of the issues I found with that is class conflicts when back-porting
>> the @GET / @POST / etc annotations, so we could only use those if we
>> were prepared to mark 2.7 as the oldest core that could use the
>> annotations, whereas we can make new annotations in a separate package
>> available as far back as Stapler 1.180 == Jenkins 1.455 (or worst case
>> Stapler 1.237 == Jenkins 1.651)
>>
>> Now we could introduce new annotations without the @Stapler prefix, but
>> then your code complete would confuse you between
>> @org.kohsuke.stapler.annotations.GET and @org.kohsuke.stapler.verbs.GET
>> plus we still need something to give a hint that the annotation is implying
>> Stapler's involvement (at least from my perspective)
>>
>>
>> - I had thought about saying that the class level @StaplerObject
>> should be enough of a flag that you should expect the other annotations...
>> but the class annotation will be inherited, so you may not see it until
>> you
>> look at the super-class... and @Path will conflict with
>> java.nio.file.Path... that might work with @Staple (and @Staples as
>> the container) but while cute they do not scream to the new developers
>> that
>> these are involved in url binding.
>>
>> NOTE: In this context I see this change as being entirely opt-in. Plugin
>> developers should not have to go adding the annotations - though we would
>> probably apply them in Jenkins core to assist new developers.
>>
>>
>> - If we go with the Stapler prefix, would it make sense to
>> consolidate all the annotations with that prefix?
>>
>> - I am not convinced for the case of @ExportedBean and @Exported,
>> these reflect a different cross-cutting concern and as such the pair
>> seem
>> named well from my PoV
>> - The @JavaScriptMethod / @WithWellKnownURL annotations might be
>> worthy of consolidation if we can determine better names.
>> - The parameter binding annotations such as @AncestorInPath,
>> @Header, @QueryParameter and @InjectedParameter I think are fine
>> where they are as they will only be on an action method which already
>> has
>> the @StaplerPOST etc indicator.
>> - The meta-annotation @InterceptorAnnotation should not be
>> consolidated, in any case we could not consolidate it and retain usage
>> against older cores
>> - The other annotations are likely rarely used, but if we can find
>> good names and people think they are generically useful rather than
>> single
>> use-case hacks added into the stapler API, I think consolidation might
>> make
>> the features more widely used.
>>
>> So, over to you the community of Jenkins developers:
>>
>> 1. Would this change have helped you get started quicker?
>> 2. Would this change help you even now?
>> 3. How ugly are my proposed annotation names? Can you provide a less
>> ugly scheme of names?
>> 4. Anything else?
>>
>> Stephen
>>
>
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