% Overview of Implementation of the CDT AdditionalLanguages Extension Point

The following, from an e-mail to the CDT copied to photran-dev, is an
alternative description of how we modified the CDT to include this
extension point.

\begin{verbatim}
1. Add an AdditionalLanguages extension point to the Core's plugin.xml and AdditionalLanguages.exsd to the Core's schema folder

   Extend via <language class="my.plugin.XyzLanguage">
   where XyzLanguage implements IAdditionalLanguage (see below)

2. Add a package org.eclipse.cdt.core.addl_langs containing:

   IAdditionalLanguage
        public interface IAdditionalLanguage {
          public String getName();
          public boolean matchesSourceContentType(String contentTypeID);
          public Collection/*<String>*/ getRegistedContentTypeIds();
          public IModelBuilder createModelBuilder(TranslationUnit tu,
              Map newElements);
        }

   AdditionalLanguagesExtension.java
        Singleton; provides access to the extension point
        Methods:
            public Iterator/*<IAdditionalLanguage>*/ iterator()
            public void processAdditionalLanguages(
                IAdditionalLanguageCallback callback)
            public boolean someAdditionalLanguageMatchesContentType(
                String contentTypeID)
            public IAdditionalLanguage getLanguageForContentType(
                String contentTypeID)

   AdditionalLanguagesIterator.java -- see iterator() above
        Implements Iterable/*<IAdditionalLanguage>*/

   IAdditionalLanguageCallback -- see processAdditionalLanguages() above
        Allows you to perform some arbitrary action on each contributed
            IAdditionalLanguage

   IModelBuilder
        Each extension language provides a model builder this way
        Single method:
            public abstract Map parse(boolean quickParseMode)
                throws Exception;

   IAdditionalLanguageElement (extends ICElement)
        Allows you to extend the ICElement hierarchy
        Methods:
            public abstract Object getBaseImageDescriptor();
            - The return type should really be ImageDescriptor,
              but I don't want to make the Core depend on JFace

3. Change content type checking to use extension point...
   i.   CoreModel#getRegistedContentTypeIds
   ii.  CCorePlugin#getContentType
   iii. TranslationUnit#isSourceUnit
   iv.  CoreModel#isValidSourceUnitName
   v.   CoreModel#isValidTranslationUnitName

   The change each of these is just a line or two -- usually a call to
   AdditionalLanguagesExtension#someAdditionalLanguageMatchesContentType

4. Make CModelBuilder implement IModelBuilder (no substantive change)

5. Change the beginning of TranslationUnit#parse(Map):
        IModelBuilder modelBuilder;
        IAdditionalLanguage lang = AdditionalLanguagesExtension
            .getInstance()
            .getLanguageForSourceContentType(fContentTypeID);
        if (lang != null)
            modelBuilder = lang.createModelBuilder(this, newElements);
        else
            modelBuilder = new CModelBuilder(this, newElements);

6. Make CElementInfo public (rather than default)

7. Make CElementInfo#setIsStructureKnown public (rather than protected)

8. Add this to the top of CElementImageProvider#getBaseImageDescriptor:
   if (celement instanceof IAdditionalLanguageElement)
     return (ImageDescriptor)
       ((IAdditionalLanguageElement)celement).getBaseImageDescriptor();
\end{verbatim}