How to generate code for a XExpression subtype?

Question

I have a simple DSL that should generate async code for expressions (this is the simplest example I could come up with to illustrate my point). I just added to the scripting example an new async statement:

grammar org.xtext.scripting.Scripting with org.eclipse.xtext.xbase.Xbase

generate scripting "http://www.xtext.org/scripting/Scripting"
import "http://www.eclipse.org/xtext/xbase/Xbase" as xbase

Script returns xbase::XBlockExpression:
    {Script}
    (expressions+=XExpressionOrVarDeclaration ';'?)*;

XExpression returns xbase::XExpression:
    super | Async
;

Async:
    'async' expression=XExpression
;

The idea would be that the async code is executed in another thread.

My question is, how can I generate code for the Async.expression using the ScriptingJvmModelInferrer?

In the simplest case I would just wrap the code from the Async.expression like this?

    AsyncRunner.exec(new Runnable() {
        @Override
        public void run() {
            // the Async.expression would end up here
        }
    })

Where is the hook to do that?

Answer 1

If you extend Xbase you ususally don't apapt the JvmModelInferrer for Compilation but you extend XbaseTypeComputer and XbaseCompiler.doInternalToJavaStatement/internalToConvertedExpression (depending on what you actually introduce)

Answer 2

You have to make 3 changes:

1. Extend the compiler to deal with your language. The key point is to handle the Async expression.

   class ScriptingCompiler extends XbaseCompiler {
   
       override protected doInternalToJavaStatement(XExpression expr, ITreeAppendable it, boolean isReferenced) {
           switch expr {
               Async : {
                   newLine
                   append('''
                       AsyncRunner.exec(new Runnable() {
                         @Override
                         public void run() {''')
                   expr.expression.doInternalToJavaStatement(it, false)
                   newLine
                   append('}});')
   
               }
   
               default :
                   super.doInternalToJavaStatement(expr, it, isReferenced)
           }
       }
   
       override protected internalToConvertedExpression(XExpression obj, ITreeAppendable it) {
           if (hasName(obj))
               append(getName(obj))
           else 
               super.internalToConvertedExpression(obj, it) 
       }
   }
   

2. The type of the expression has to be specified

   class ScriptingTypeComputer extends XbaseWithAnnotationsTypeComputer {
   
       override computeTypes(XExpression expression, ITypeComputationState state) {
           if(expression instanceof Async) {
               super.computeTypes(expression.expression, state);
           } else {
               super.computeTypes(expression, state)
           }
       }
   }
   

3. Both extensions have to be injected:

   class ScriptingRuntimeModule extends AbstractScriptingRuntimeModule {
       def Class<? extends XbaseCompiler> bindXbaseCompiler() {
           return ScriptingCompiler
       }
   
       def Class<? extends ITypeComputer> bindITypeComputer() {
           return ScriptingTypeComputer
       }
   }