Benjamin Cabé

Model my PDE!

Benjamin Cabé

I’ve been working for quite a while on finding solutions to the problems we are having in PDE as soon as we need to add support for new OSGi headers, to create new editors for cheatsheet files, p2 categories, etc.

Declarative Services tooling is a good illustration of all these problems. As part of the Google Summer of Code 2008, Rafael Oliveira worked on the creation of some cool tooling to help people wanting to use OSGi Declarative Services. This tooling is great, and available in Eclipse Galileo as many of you may know but, unfortunately, it introduces a lot of boilerplate code (Java model of what a DS component is, Java model of what the textual representation of a DS component is, JFace label and content providers, etc.)

Indeed, since day 1 of PDE, despite the fact there is a sort of generic framework behind PDE (undo/redo support for operations done both programmatically or through the UI/text editors, compiler to check models consistency and create markers, outline, etc.), it is, and always has been kind of a pain to “instantiate” this framework for each new usecase.

People familiar with EMF, and modeling technologies in general, are probably thinking right now that the framework behind PDE should probably model-based, and of course they are right! That’s exactly the purpose of the ongoing “model my PDE” work being done in the PDE incubator. In this post, I will quickly explain what is currently available in HEAD of the project, further explanations may come in later posts (by the way, feel free to ask precisions on specific topics!).

Generic Forms editor

The org.eclipse.pde.emfforms bundle proposes some abstractions of what is generally needed to create a Forms editor for any kind of EObject. Thanks to EMF.Edit and Databinding framework, it makes it really simple –sometimes you won’t even need to write a single line of code– to create your UI and bind it to the model, display the errors on your model, show an outline, and stuff.

Since the project is still incubating, there is of course no clear API of this bundle at the moment, but if you need to quickly hack a model editor, you should probably have a look at it, and at the “exemplary” implementation which has been done for the “next-gen” DS Component editor.

A non-exhaustive list of the feature provided by this framework (coupled to the features of EMF/EMF.Edit/Databinding and Forms) would be:

Extensibility

There are many OSGi vendors who work on their own implementation of the standard, and they obviously need tooling for these specificities. In an ideal world, they should be able to extend vanilla PDE instead of reinventing the wheel. We, at PDE, expose some APIs for people to do that (SpringSource Tool Suite proposes tooling for SpringDM, and it is built on top of PDE), but there are many things that are still internal. Our models, our editors, our compilers, are not really designed to be extensible. A model-based approach is the right solution to this lack of extensibility:

<extension point="org.eclipse.emf.validation.constraintProviders">
      <category
            id="org.eclipse.pde.ds.builder.validation"
            mandatory="true"
            name="Declarative Services Validation">
      </category>
      <constraintProvider cache="true">
         <package
               namespaceUri="http://www.osgi.org/xmlns/scr/v1.1.0">
         </package>
         <constraints
               categories="org.eclipse.pde.ds.builder.validation">
            <constraint
                  class="o.[...].ComponentMethodsAreValidAndAccessible"
                  id="o.[...].constraintComponentMethodsAreValidAndAccessible"
                  lang="Java"
                  mode="Live"
                  name="Components methods validation"
                  severity="ERROR"
                  statusCode="2">
               <message>
                  Method {0}: {1}
               </message>
               <target class="Component">
                  <event name="Set">
                     <feature name="activate">
                     </feature>
                  </event>
                  <!-- ... -->
               </target>
            </constraint>
         </constraints>
      </constraintProvider>
   </extension>

Model-aware builder

In order to report errors to the end-user, the editor performs live validation (thus the nice Forms decorators in the screencast below), but there is also a specific builder (once again, designed to be extensible) listening for model changes, and calling EMF Validation behind the scene to check the consistency and create resource markers for every encountered problem.

Screencast

A screencast being IMHO worth a thousand words, here is a live demo of the DS Editor:

If you want to play with this  “experimental” tool, you can install in your SDK the experimental feature served by build.eclipse.org and corresponding to the result of continuous integration of the HEAD of the project, thanks to Hudson and Athena!

I guess the next important step is now to find an elegant way to propose a Source tab which, as you may have noticed, is almost the only feature being present in the Galileo editor and not in this prototype. Another important step will also be to write the Xtext grammar of an OSGi Manifest, and leverage this “EMF-Forms” framework to propose a cool and extensible editor on top of a Manifest 🙂

Exit mobile version