I am trying to create a custom language that extends the groovy language. One way I am exploring is to associate some of the groovy extensions with my new custom language through the extensions section of the plugin.xml. However, when doing so I receive errors stating that: "Language Language: Groovy doesn't participate in view provider com.intellij.psi.SingleRootFileViewProvider@f43af5: [Language: easyb]". Looking at how the groovy plugin prior to Diana allowed for multipe languages within GSP files I see that the GroovyLanguage overrides the createViewProvider method and returns a type of GspFileViewProvider which extends MultiplePsiFilesPerDocumentFileViewProvider and adds valid composed languages into a set returned by getRelevantLanguages().
I think that I want to do something like this in my custom language, but can't see the MultiplePsiFilesPerDocumentFileViewProvider file in Diana, or any concrete implementations of FileViewProvider for that matter. Am I on the right path here? And if so, what is the replacement for MultiplePsiFilesPerDocumentFileViewProvider in Diana?