Content assist is one a major feature of an IDE and Xtext provides support for this capability in SADL. Providing meaningful content assistance in SADL is complicated by the fact that what can next in a SADL model file depends on what the ontology contains. The purpose of this document is to provide an overview of how content assistance is implemented in SADL Version 3.
Content assist is architected to work in both the Eclipse environment and in WebSADL. Therefore the control flow goes through the Eclipse-independent IdeContentProposalProvider and from there to the _createProposals method (and others) in the SadlIdeContentProposalProvider class in the com.ge.research.sadl.ide project.
The grammar definition in Sadl.xtext allows Xtext to identify keywords that can appear next after the current cursor location in a fairly standard way, but identifying which SadlResources (named concepts in the model and the model's imports) is very contextual. The _createProposals method uses the SADL Scopes to get a list of all of the SadlResources known to the model. These are then filtered, ultimately coming down to the getCrossReferenceFilter method in the ProposalProviderFilterProvider class. This method uses the SadlOntologyContextProvider class's getOntologyContext method to create an instance of the Context class. The "currentModel" is the last EObject successfully identified in the parse tree prior to the current cursor location. In some instances this will be the top-level SadlModel. At other times it will be a lower-level EObject. This method iterates over the contents of filtered grammar elements and gets a "key" indicative of where one might be, grammar-wise. Depending on the value of the "key", different instances of Context are created.
If no instance of Context is generated, the SadlResource the method returns true, meaning that the SadlResource should be added to the content assist proposals. Otherwise, if the "key" is contained by the ONTOLOGY_DEPENDENT_CONTEXT_IDS list, the validate method of the JenaBasedSadlModelProcessor is called to determine if the SadlResource is viable. For example, if the cursor is at the end of the incomplete statement "Dog is atype of " then only SadlResources that are of type OntConceptType.CLASS are viable.
If the SadlResource under consideration is not viable, an error message is added to the instance of ProposalProviderValidationAcceptor that is passed into the call to validate. Upon return from the call, only those candidates that have no errors added to the acceptor are added to the set of proposals.