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POXText Chained Dependencies in Type Inference
 

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    <p>In my experiments, it appears that XText cannot resolve variable types when there is a chain of dependencies across multiple XExpression blocks.</p> <p>A minimal example, to illustrate. I have a grammar:</p> <pre><code>grammar eg.types.inference.TypeInferenceExample with org.eclipse.xtext.xbase.Xbase generate typeInferenceExample "example.org/types/inference/TypeInferenceExample" Model: blocks += Block* ; Block: '{' 'name' ':' name=QualifiedName 'from' ':' ('none' | from=[Block|QualifiedName]) 'block' ':' expression=XBlockExpression '}' ; </code></pre> <p>An interface:</p> <pre><code>package eg.lib; public interface IModelBlock { public void push(org.eclipse.xtext.xbase.lib.Pair&lt;String, ?&gt; toPush); } </code></pre> <p>And a JvmModelInferrer:</p> <pre><code>package eg.types.inference.jvmmodel import com.google.inject.Inject import eg.lib.IModelBlock import eg.types.inference.typeInferenceExample.Block import eg.types.inference.typeInferenceExample.Model import org.eclipse.xtext.xbase.XBinaryOperation import org.eclipse.xtext.xbase.XExpression import org.eclipse.xtext.xbase.XFeatureCall import org.eclipse.xtext.xbase.XStringLiteral import org.eclipse.xtext.xbase.jvmmodel.AbstractModelInferrer import org.eclipse.xtext.xbase.jvmmodel.IJvmDeclaredTypeAcceptor import org.eclipse.xtext.xbase.jvmmodel.JvmTypesBuilder class TypeInferenceExampleJvmModelInferrer extends AbstractModelInferrer { @Inject extension JvmTypesBuilder def dispatch void infer(Model model, IJvmDeclaredTypeAcceptor acceptor, boolean isPreIndexingPhase) { model.blocks.forEach [block | acceptor.accept(block.toClass(block.name)).initializeLater [ superTypes += block.newTypeRef(typeof(IModelBlock)) members += block.toMethod("invoke", newTypeRef(Void::TYPE)) [ if (block.from != null) { block.from.pushType.forEach [p | parameters += block.toParameter(p.key, p.value) ] } body = block.expression ] ] ] } def private pushType(Block block) { return block.eAllContents.filter[ // List of push calls in this Block it instanceof XFeatureCall &amp;&amp; (it as XFeatureCall).concreteSyntaxFeatureName.equals("push") ].map [ val call = it as XFeatureCall // Add entry for push call as an OutputDeclaration return call.featureCallArguments.map[ if (!(it instanceof XBinaryOperation)) { throw new RuntimeException("Must push using -&gt; operator") } val key = (it as XBinaryOperation).leftOperand val value = (it as XBinaryOperation).rightOperand return key.name -&gt; value.inferredType ] ].head } def private String name(XExpression literal) { if (!(literal instanceof XStringLiteral)) { throw new UnsupportedOperationException("Literal was not a string literal") } return (literal as XStringLiteral).value } } </code></pre> <p>When I create a simple example for this DSL, such as:</p> <pre><code>{ name : BlockOne from : none block : { val i = 42 * 3.6 push("index" -&gt; i) } } { name : BlockTwo from : BlockOne block : { val res = "Another Value from " + index push("result" -&gt; res) } } </code></pre> <p>Code is generated just fine (type inference successfully works out the types of <code>index</code> and <code>res</code> in generating the output Java). I am using the pairs in the call to <code>push</code> on <code>BlockOne</code> to infer an interface on the invoke method for <code>BlockTwo</code>. This <code>push</code> method comes from the <code>IModelBlock</code> interface above. If I add a third Block to this example, thus:</p> <pre><code>{ name : BlockThree from : BlockTwo block : { val out = "This one came from: " + result push("out" -&gt; out) } } </code></pre> <p>Inference fails, with an <code>UnsupportedOperationException: TODO: import a functional handle on the type resolution that delegates to the best available (current, but evolving) result</code> (from <code>OnChangeEvictingCache.execWithoutCacheClear</code>, <code>CachingBatchTypeResolver.resolveTypes</code>).</p> <p><strong>Is there some other technique I should use to derive the types of variables which have chained dependencies like this in XText?</strong></p> <p>Thanks for the help!</p>
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