Opening a class that does not exist should raise an error

[echebbi]

Fix #19.

1. Enhance the type checker to show an error when opening a class that does not exist:

behavior helloworld;

open class Foo {

}

Here, Foo can be:

• a static class defined within an Ecore metamodel,
• a runtime class defined in the same .ale file,
• a runtime class defined in another .ale file.

Otherwise, an error is shown.

2. Enhance the type checker to show a warning when opening a class that has namesakes

behavior helloworld;

open class Foo {

}

Will raise a warning if a class Foo is defined:

• in a package not called helloworld,
• in an .ale file which behavior is not helloworld

[echebbi]

For public record: the code used to check whether the opened class exists is not 100% reliable at the moment. Indeed, when building the AST, if the base class does not exist then the type of the opened class is set to EClassifier by default (see ModelBuilder#resolve(String)).

I first decided to assume that each time an opened class has EClassifier for base class then that would mean that in fact the class does not exist (see OpenClassValidator#validateExtendedClassExists). However some tests are actually opening EClassifier and thus started to fail.

I believe that the proper way to solve this would be to update the resolve method to return an Optional<EClassifier>. The problem is that the current code assumes that ExtendedClass#getBaseClass always returns a valid value which would not be the case anymore. As a result we have to change the code at multiple different places and I currently do not have the time for that.

[dvojtise]

Looks good to me

[dvojtise]

I fully agree about your comment "resolve method should return an Optional"

the line bellow

ale-lang/plugins/org.eclipse.emf.ecoretools.ale.core/src/org/eclipse/emf/ecoretools/ale/core/parser/visitor/ModelBuilder.java

Line 554 in fa71c1f

//TODO: else error

clearly states that this is an error case that is not correctly handled.

I suggest opening an issue to track its resolution.