Xtext基数元模型

Question

I am currently working on a project, where I am creating a feature model out of Xtext grammar. My task is to transform grammar syntax into a CSV file importable into eclipse plug-in pure::variants.

Feature model is basicaly tree of features. These features are different types ( mandatory, optional, alternative etc. ).

For constructing the tree, I am using generated ecore meta model of my xtext grammar syntax. This file ( .ecore ) is basically a XML file with objects of the grammar. It is consistent, simple and easy to create tree out of.

My problem is, that I need to assign types ( mandatory, alternative etc. ) to the nodes of my created tree. These types of features correspond to a cardinality operators. These operators are written in xtext grammar like this: ´(no operator)´, ´?´, ´*´ and ´+´ ( this can be seen in xtext user manual section 2.1.3 https://www.eclipse.org/Xtext/documentation/1_0_1/xtext.pdf ). Problem is, that these cardinalities of xtext grammar don't seem to be anywhere to find. I thought that they would appear in .ecore or .genmodel files, but there are no cardinalities at all.

I imagine that if xtext is able to check and control these cardinalities, it has to have some kind of meta model, where these cardinalities can be seen and are easily gettable ( something like .xml file similiar to .ecore or .genmodel file).

So my question is: Is there some kind of xtext generated file, which contains these cardinalities? If there is not, I would have to somehow get these cardinalities out of grammar itself, but it would be unneccessarily time consuming and complicated, maybe even impossible, because written grammar doesn't fully correspond with ecore metamodel I am getting my feature tree out of and is really complex.

Only generated file I was able to find, which contains something "maybe useful" is generated file XXXXGrammarAccess.java ( XXXX stands for name of the grammar ), which is complex generated file, with a lot of library depedencies and I have no idea how to get these cardinalities out of that or if it is even possible. I imagine that there is a possibility, because this file uses a lot of IGrammarAccess methods, such as getRule(), getKeyword() and more, but I am not able to use this file, or print something out of it, because it is a generated file and I am not able to run it on itself.

If there is not some kind of meta model I am looking for, is there any possibility to somehow get these cardinalities different way during generating?

Thank you very much for your answers.

Answer 1

first of all the cardinalities in the metamodel and the grammar do not have to match 100%. the cardinality validation in the parser is different than the one in ecore.

the lower cardinality of 1 (for required) is not there to prevent really ugly error messages. the :1 or :-1 (=*) is reflected in the ecore though.

this was a deliberate decision when Xtext was created 10 years ago.

the grammar access just gives you access to the grammar at runtime.

can you elaborate why you actually care?

Answer 2

The Xtext grammar is itself a model, an instance of http://www.eclipse.org/2008/Xtext . (It used to be possible to demonstrate this by opening a *.xtext file with the Sample Reflective Ecore Editor, but unfortunately the use of classpath: URIs has broken it again.) Nonetheless you can open a *.xtext file programmatically as an EMF Resource and see everything that is in the grammar. See https://git.eclipse.org/c/ocl/org.eclipse.ocl.git/tree/examples/org.eclipse.ocl.examples.xtext2lpg/src/org/eclipse/ocl/examples/xtext2lpg/xtext2xbnf.qvto for the first stage of a transformation chain that starts by reading an Xtext grammar and ends up with an LPG grammar.