Tag Archives: emf

Switching to Xcore in your Xtext language

This is a followup of my previous post, Switching from an inferred Ecore model to an imported one in your Xtext grammar. The rationale for switching to manually maintained metamodel can be found in the previous post. In this post, instead of using an Ecore file, we will use Xcore,

Xcore is an extended concrete syntax for Ecore that, in combination with Xbase, transforms it into a fully fledged programming language with high quality tools reminiscent of the Java Development Tools. You can use it not only to specify the structure of your model, but also the behavior of your operations and derived features as well as the conversion logic of your data types. It eliminates the dividing line between modeling and programming, combining the advantages of each.

I took inspiration from Jan Köhnlein’s blog post; after switching to a manually maintained Ecore in Xsemantics, I felt the need to further switch to Xcore, since I had started to write many operation implementations in the metamodel, and while you can do that in Ecore, using Xcore is much easier 🙂 Thus in my case I was starting from an existing language, not to mention the use of Xbase (not covered in Jan’s post). Things were not easy, but once the procedure works, it is easily reproducible, and I’ll detail this for a smaller example.

So first of all, let’s create an Xtext project, org.xtext.example.hellocustomxcore, (you can find the sources of this example online at https://github.com/LorenzoBettini/Xtext2-experiments); the grammar of the DSL is not important: this is just an example. We will first start developing the DSL using the automatic Ecore model inference and later we will switch to Xcore.

(the language is basically the same of the previous post).

The grammar of this example is as follows:

and we run the MWE2 generator.

To have something working, we also write an inferrer

With this DSL we can write programs of the shape (nothing interesting, this is just an example)

Now, let’s say we want to check in the validator that there are no elements with the same name; since both “Hello” and “Greeting” have the feature name, we can introduce in the metamodel a common interface with the method getName(). OK, we could achieve this also by introducing a fake rule in the Xtext grammar, but let’s do that with Xcore.

Switching to Xcore

Of course, first of all, you need to install Xcore in your Eclipse.

Before we use the export wizard, we must make sure we can open the generated .genmodel with the “EMF Generator” editor (otherwise the export will fail). If you get an error opening such editor about resolving proxy to JavaJVMTypes.ecore like in the following screenshot…

gemodel_problems

..then we must tweak the generated .genmodel and add a reference to JavaVMTypes.genmodel: open HelloXcore.genmodel with the text editor, and search for the part (only the relevant part of the line is shown)

and add the reference to the JavaVMTypes.genmodel:

Since we’re editing the .genmodel file, we also take the chance to modify the output folder for the model files to emf-gen (see also later in this section for adding emf-gen as a source folder):

And we remove the properties that relate to the edit and the editor plug-ins (since we don’t want to generate them anyway):

Now save the edited file, refresh the file in the workspace by selecting it and pressing F5 (yes, also this operation seems to be necessary), and this time you should be able to open it with the “EMF Generator” editor. We can go on exporting the Xcore file.

We want the files generated by Xcore to be put into the emf-gen source folder; so we add a new source folder to our project, say emf-gen, where all the EMF classes will be generated; we also make sure to include such folder in the build.properties file.

First, we create an .xcore file starting from the generated .genmodel file:

  • navigate to the HelloXcore.genmodel file (it is in the directory model/generated)
  • right click on it and select “Export Model…”
  • in the dialog select “Xcore”
    gemodel_export1
  • The next page should already present you with the right directory URI
    gemodel_export2
  • In the next page select the package corresponding to our DSL, org.xtext.example.helloxcore.helloxcore (and choose the file name for the exported .xcore file corresponding Helloxcore.xcore file)
    gemodel_export3
  • Then press Finish
  • If you get an error about a missing EObjectDescription, remove the generated (empty) Helloxcore.xcore file, and just repeat the Export procedure from the start, and the second time it should hopefully work

gemodel_export4

The second time, the procedure should terminate successfully with the following result:

  • The xcore file, Helloxcore.xcore has been generated in the same directory of the .genmodel file (and the xcore file is also opened in the Xcore editor)
  • A dependency on org.eclipse.emf.ecore.xcore.lib has been added to the MANIFEST.MF
  • The new source folder emf-gen is full of compilation errors

gemodel_export5

Remember that the model files will be automatically generated when you modify the .xcore file (one of the nice things of Xcore is indeed the automatic building).

Fixing the Compilation Errors

These compilation errors are expected since Java files for the model are both in the src-gen and in the emf-gen folder. So let’s remove the ones in the src-gen folders (we simply delete the corresponding packages):

gemodel_export6

After that, everything compile fines!

Now, you can move the Helloxcore.xcore file in the “model” directory, and remove the “model/generated” directory.

Modifying the mwe2 workflow

In the Xtext grammar, HelloXcore.xtext, we replace the generate statement with an import:

The DirectoryCleaner fragment related the “model” directory should be removed (otherwise it will remove our Helloxcore.xcore file as well); and we don’t need it anymore after we manually removed the generated folder with the generated .ecore and .genmodel files.

Then, in the language part, you need to loadResource the XcoreLang.xcore, the Xbase and Ecore ecore and genmodel, and finally the xcore file you have just exported, Helloxcore.xcore.

We can comment the ecore.EMFGeneratorFragment (since we manually maintain the metamodel from now on).

The MWE2 files is now as follows (I highlighted the modifications):

Before running the workflow, you also need to add org.eclipse.emf.ecore.xcore as a dependency in your MANIFEST.MF.

We can now run the mwe2 workflow, which should terminate successfully.

We must now modify the plugin.xml (note that there’s no plugin.xml_gen anymore), so that the org.eclipse.emf.ecore.generated_package extension point contains the reference to the our Xcore file:

Fixing Junit test problems

As we saw in the previous post, Junit tests do not work anymore with errors of the shape

All we need to do is to modify the StandaloneSetup in the src folder (NOT the generated one, since it will be overwritten by subsequent MWE2 workflow runs) and override the register method so that it performs the registration of the EPackage (as it used to do before):

And now the Junit tests will run again.

Modifying the metamodel with Xcore

We can now customize our metamodel, using the Xcore editor.

For example, we add the interface Element, with the method getName() and we make both Hello and Greeting implement this interface (they both have getName() thus the implementation of the interface is automatic).

Using the Xcore editor is easy, and you have content assist; as soon as you press save, the Java files will be automatically regenerated:

xcore_modify1

We also add a method getElements() to the Model class returning an Iterable<Element>(containing both the Hello and the Greeting objects). This time, with Xcore, it is really easy to do so (compare that with the procedure of the previous post, requiring the use of EAnnotation in the Ecore file), since Xcore uses Xbase expression syntax for defining the body of the operations (with full content assist, not to mention automatic import statement insertions). See also the generated Java code on the right:

xcore_modify2

And now we can implement the validator method checking duplicates, using the new getElements() method and the fact that now both Hello and Greeting implement Element:

That’s all! I hope you found this tutorial useful 🙂

 

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Switching from an inferred Ecore model to an imported one in your Xtext grammar

When you use Xtext for developing your language the Ecore model for the AST is automatically derived/inferred from the grammar. If your DSL is simple, this automatic meta-model inference is usually enough. However, there might be cases where you need more control on the meta-model and in such cases you will want to switch from an inferred Ecore model to a an imported one, which you will manually maintain. This is documented in the Xtext documentation, and in some blog posts. When I needed to switch to an imported Ecore model for Xsemantics, things have not been that easy, so I thought to document the steps to perform some switching in this tutorial, using a simple example. (I should have talked about that in my Xtext book, but at that time I ran out of pages so there was no space left for this subject 🙂

So first of all, let’s create an Xtext project, org.xtext.example.hellocustomecore, (you can find the sources of this example online at https://github.com/LorenzoBettini/Xtext2-experiments); the grammar of the DSL is not important: this is just an example. We will first start developing the DSL using the automatic Ecore model inference and later we will switch to an imported Ecore.

The grammar of this example is as follows (to make things more interesting, we will also use Xbase):

and we run the MWE2 generator.

To have something working, we also write an inferrer

With this DSL we can write programs of the shape (nothing interesting, this is just an example)

Now, let’s say we want to check in the validator that there are no elements with the same name; since both “Hello” and “Greeting” have the feature name, we can introduce in the Ecore model a common interface with the method getName(). OK, we could achieve this also by introducing a fake rule in the Xtext grammar, but let’s switch to an imported Ecore model so that we can manually modify that.

Switching to an imported Ecore model

First of all, we add a new source folder to our project (you must create it with File -> New -> Source Folder, or if you create it as a normal folder, you then must add it as a source folder with Project -> Properties -> Lava Build Path: Source tab), say emf-gen, where all the EMF classes will be generated; we also make sure to include such folder in the build.properties file:

Remember that, at the moment, the EMF classes are generated into the src-gen folder, together with other Xtext artifacts (e.g., the ANTLR parser):

imported-ecore-project-layout1

Xtext generates the inferred Ecore model file and the GenModel file into the folder model/generated

imported-ecore-project-layout2

This is the new behavior introduced in Xtext 2.4.3 by the fragment ecore.EMFGeneratorFragment that replaces the now deprecated ecore.EcoreGeneratorFragment; if you still have the deprecated fragment in your MWE2 files, then the Ecore and the GenModel are generated in the src-gen folder.

Let’s rename the “generated” folder into “custom” (if in the future for any reason we want to re-enable Xtext Ecore inference, our custom files will not be overwritten):

imported-ecore-project-layout3

NOTE: if you simply move the .ecore and .genmodel file into the directory model, you will not be able to open the .ecore file with the Ecore editor: this is due to the fact that this Ecore file refers to Xbase Ecore models with a relative path; in that case you need to manually adjust such references by opening the .ecore file with the text editor.

From now on, remember, we will manually manage the Ecore file.

Now we change the GenModel file, so that the EMF model classes are generated into emf-gen instead of src-gen:

imported-ecore-genmodelWe need to change the MWE2 file as follows:

  • Enable the org.eclipse.emf.mwe2.ecore.EcoreGenerator fragment that will generate the EMF classes using our custom Ecore file and GenModel file; indeed, you must refer to the custom GenModel file; before that we also run the DirectoryCleaner on the emf-gen folder (this way, each time the EMF classes are generated, the previous classes are wiped out); enable these two parts right after the StandaloneSetup section;
  • Comment or remove the DirectoryCleaner element for the model directory (otherwise the workflow will remove our custom Ecore and GenModel files);
  • In the language section we load our custom Ecore file,
  • and we disable ecore.EMFGeneratorFragment (we don’t need that anymore, since we don’t want the Ecore model inference)

The MWE2 files is now as follows (I highlighted the modifications):

We add the dependency org.eclipse.xtext.ecore in the MANIFEST.MF:imported-ecore-manifestIn the Xtext grammar we replace the generate statement with an import statement:

Now we’re ready to run the MWE2 workflow, and you should get no error (if you followed all the above instructions); you can see that now the EMF model classes are generated into the emf-gen folder (the corresponding packages in the src-gen folders are now empty and you can remove them):

imported-ecore-project-layout4

We must now modify the plugin.xml (note that there’s no plugin.xml_gen anymore), so that the org.eclipse.emf.ecore.generated_package extension point contains the reference to the new GenModel file:

 

If you try the editor for the DSL it will still work; however, the Junit tests will fail with errors of this shape:

That’s because the generated StandaloneSetup does not register the EPackage anymore, see the diff:

imported-ecore-diff

All we need to do is to modify the StandaloneSetup in the src folder (NOT the generated one, since it will be overwritten by subsequent MWE2 workflow runs) and override the register method so that it performs the registration of the EPackage:

And now the Junit tests will run again.

Modifying the Ecore model

We can now customize our Ecore model, using the Ecore editor and the Properties view.

For example, we add the interface Element, with the method getName() and we make both Hello and Greeting implement this interface (they both have getName() thus the implementation of the interface is automatic).

imported-ecore-custom-ecore1 imported-ecore-custom-ecore2 imported-ecore-custom-ecore3

We also add a method getElements() to the Model class returning an Iterable<Element> (containing both the Hello and the Greeting objects)

imported-ecore-custom-ecore4

and we implement that method using an EAnnotation, using the source “http://www.eclipse.org/emf/2002/GenModel” and providing a body

imported-ecore-custom-ecore5 imported-ecore-custom-ecore6

With the following implementation

Let’s run the MWE2 workflow so that it will regenerate the EMF classes.

And now we can implement the validator method checking duplicates, using the new getElements() method and the fact that now both Hello and Greeting implement Element:

That’s all! I hope you found this tutorial useful 🙂

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