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POException in generated editor: Xtext bug or error in grammar?
 

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  1. POException in generated editor: Xtext bug or error in grammar?
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    <p>After moving to Xtext 2.4.2 and Eclipse Kepler, a problem appeared in the editor of our DSL. Everything was perfectly working before (Xtext 2.3.x, Juno).</p> <p>Our DSL editor throws a ClassCastException when we edit an initialization list: <code>[1,2,3]</code> <img src="https://i.stack.imgur.com/d8RPV.png" alt="Xtext Error Pop-up"></p> <p><strong>Steps to reproduce:</strong></p> <ol> <li>Create a new "Xtext State-Machine Example" project</li> <li>Edit the grammar with the one below</li> <li>Delete the package org.eclipse.xtext.example.fowlerdsl.generator (it will be regenerated at 4.)</li> <li>Run the org.eclipse.xtext.example.fowlerdsl.GenerateStatemachine.mwe2 workflow</li> <li>Run the eclipse application</li> <li>Create a new file (example.statemachine) in an empty project and copy the folowing content</li> </ol> <p><strong>Grammar:</strong></p> <pre class="lang-xtext prettyprint-override"><code>grammar org.eclipse.xtext.example.fowlerdsl.Statemachine with org.eclipse.xtext.common.Terminals generate statemachine "http://www.eclipse.org/xtext/example/fowlerdsl/Statemachine" Statemachine : {Statemachine} (vars += VarDeclWithOptionalInit)* ; VarDeclWithOptionalInit returns Variable: VarDecl ('=' value=AstExpression)? ; VarDecl returns Variable: 'var' name = ID ; AstExpression: ExpressionList | {AstExpression} INT ; ExpressionList: '[' expressions+=AstExpression (',' expressions+=AstExpression)* ']' ; </code></pre> <p><strong>Content of example.statemachine</strong></p> <pre class="lang-js prettyprint-override"><code>//Adding space between chars inside [] cause Exception var example1 = [1, 2, 3] //Doing the same in [10, 20] or [30, 40] is Ok, but modifying //the top-level list cause the Exception var example2 = [[10, 20], 0, [30, 40], 1, 2] </code></pre> <p>I think the content of the example file is correct. But when I edit lists with new values, or when I add spaces around commas or values, the editor pop-up an error with a ClassCastException from the XtextReconcilierJob.</p> <p>Do you think my grammar has something wrong, or is it a bug from Xtext side ?</p> <p><strong>Additional information</strong></p> <p>I fight against this for some days, and I collected some interesting information:</p> <ul> <li>In the example, editor throws only when editing elements from the top-level list, not from inner ones (see example2 variable)</li> <li>In my tests, sometimes a <code>NullPointerException</code> was throwed earlier in the call stack. <ul> <li>I suspect the method <code>PartialParsingHelper.reparse(IParser parser, IParseResult prev, ReplaceRegion cr)</code> to have a strange behavior</li> <li>This method found the parent of the current modified element in the model, to call eSet() on this with the new value. But in our case, it try to call <code>Statemachine.eSet()</code> instead of <code>Variable.eSet()</code></li> <li>The <code>ClassCastException</code> comes from an equal feature id: <ul> <li><code>StateMachine.vars</code> has a feature id == 0</li> <li><code>Variable.value</code> has a feature id == 0</li> <li>But the 2 features have not the same type</li> </ul></li> <li>If I add some feature BEFORE value in <code>Variable</code>, the Exception thrown (earlier) is a <code>NullPointerException</code>, because <code>Variable.value</code> has a feature id == 2 or 3 when <code>StateMachine</code> has only 2 features (0 and 1)</li> </ul></li> </ul> <p><strong>StackTrace of the error:</strong></p> <pre><code>Thread [Worker-2] (Suspended (exception ClassCastException)) StatemachineImpl.eSet(int, Object) line: 128 StatemachineImpl(BasicEObjectImpl).eSet(EStructuralFeature, Object) line: 1071 PartialParsingHelper.reparse(IParser, IParseResult, ReplaceRegion) line: 161 StatemachineParser(AbstractAntlrParser).doReparse(IParseResult, ReplaceRegion) line: 136 StatemachineParser(AbstractParser).reparse(IParseResult, ReplaceRegion) line: 48 LazyLinkingResource(XtextResource).update(int, int, String) line: 220 XtextDocumentReconcileStrategy.doReconcile(IRegion) line: 125 XtextDocumentReconcileStrategy.reconcile(IRegion) line: 55 XtextReconciler.doRun(XtextResource, IProgressMonitor) line: 329 XtextReconciler.access$3(XtextReconciler, XtextResource, IProgressMonitor) line: 316 XtextReconciler$1.process(XtextResource) line: 273 XtextReconciler$1.process(Object) line: 1 XtextReconciler$1(IUnitOfWork$Void&lt;T&gt;).exec(T) line: 36 XtextDocument$XtextDocumentLocker(AbstractReadWriteAcces&lt;P&gt;).modify(IUnitOfWork&lt;T,P&gt;) line: 81 XtextDocument$XtextDocumentLocker.modify(IUnitOfWork&lt;T,XtextResource&gt;) line: 201 XtextDocument.internalModify(IUnitOfWork&lt;T,XtextResource&gt;) line: 98 XtextReconciler.run(IProgressMonitor) line: 270 Worker.run() line: 53 </code></pre>
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    1. COWhat does `ExpressionListImpl` and it's interface `ExpressionList` extend/implement?
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      1. USAaron Digulla
    2. COExpressionListImpl extends AstExpressionImpl implements ExpressionList AstExpressionImpl extends MinimalEObjectImpl.Container implements AstExpression ExpressionList extends AstExpression AstExpression extends EObject
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      1. POException in generated editor: Xtext bug or error in grammar?
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    3. COIn that case, I'm stumped. Try to ask the same question on the [Xtext forum](http://www.eclipse.org/forums/index.php?t=thread&frm_id=27). It could be a bug. Btw: +1 for the impressive collection of useful information.
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      1. POException in generated editor: Xtext bug or error in grammar?
      1. USAaron Digulla
 

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