Jump to: navigation, search

Difference between revisions of "Xtext/FAQ"

m
Line 1: Line 1:
= Generator =
+
= General  =
  
== Why do I get warnings like "warning(200): InternalFoo.g:42:3: Decision can match input such as "..." using multiple alternatives: 1, 2 As a result, alternative(s) 2 were disabled for that input" when running the generator? ==
+
= Workflow / Generator  =
  
These warnings are generated by the ANTLR code generator. Based on the rules in your grammar the ANTLR generated parser cannot disambiguate what rules to apply for a given input. You should try to refactor your grammar (see [http://www.antlr.org/pipermail/antlr-interest/2008-November/031697.html example]) or you can enable backtracking for your parser (see next question).
+
== Why do I get warnings like "warning(200): InternalFoo.g:42:3: Decision can match ..." when running the generator ?  ==
  
== OK, but I didn't get these warnings in oAW Xtext ==
+
Here's an example of the full error message:
  
Unlike in oAW Xtext the ANTLR grammar generated by TMF Xtext doesn't have [http://www.antlr.org/wiki/display/ANTLR3/Grammar+options backtracking] enabled by default. To enable backtracking you have to add a nested element <options backtrack="true"/> to the ANTLR generator fragments in your Xtext project's MWE workflow. For example:
+
<source lang="text">
 +
warning(200): InternalFoo.g:42:3: Decision can match input such as "FOO" using multiple alternatives: 1, 2
 +
As a result, alternative(s) 2 were disabled for that input
 +
</source>
 +
 
 +
These warnings are generated by the ANTLR code generator. Based on the rules in your grammar the ANTLR generated parser cannot disambiguate what rules to apply for a given input. You should try to refactor your grammar (see [http://www.antlr.org/pipermail/antlr-interest/2008-November/031697.html example]) or you can enable backtracking for your parser (see next question).
 +
 
 +
== OK, but I didn't get these warnings in oAW Xtext&nbsp;!  ==
 +
 
 +
Unlike in oAW Xtext the ANTLR grammar generated by TMF Xtext doesn't have [http://www.antlr.org/wiki/display/ANTLR3/Grammar+options backtracking] enabled by default. To enable backtracking you have to add a nested element &lt;options backtrack="true"/&gt; to the ANTLR generator fragments in your Xtext project's MWE workflow. For example:  
  
 
<source lang="xml">
 
<source lang="xml">
Line 14: Line 23:
 
       <options backtrack="true"/>
 
       <options backtrack="true"/>
 
   </fragment>
 
   </fragment>
</source>
+
</source>
 +
 
 +
== Why are generated packages from an imported grammar A duplicated in dependent grammar B&nbsp;?  ==
 +
 
 +
In addition to the import statement in B.xtext you must also configure your GenerateB.mwe workflow to let it know about the corresponding GenModels of grammar A. You do this by [http://www.eclipse.org/Xtext/documentation/0_7_0/xtext.html#UsingresourceURIstoimportexistingEPackages setting the genModels attribute] of the EcoreGeneratorFragment:
 +
 
 +
<source lang="xml">
 +
  <fragment class="org.eclipse.xtext.generator.ecore.EcoreGeneratorFragment"
 +
      genModels="platform:/resource/project/src/my/pack/SecretCompartments.genmodel"/>
 +
</source>  
  
[[Category:FAQ]]
+
[[Category:FAQ]] [[Category:Xtext]]
[[Category:Xtext]]
+

Revision as of 02:25, 17 July 2009

General

Workflow / Generator

Why do I get warnings like "warning(200): InternalFoo.g:42:3: Decision can match ..." when running the generator ?

Here's an example of the full error message:

warning(200): InternalFoo.g:42:3: Decision can match input such as "FOO" using multiple alternatives: 1, 2
As a result, alternative(s) 2 were disabled for that input

These warnings are generated by the ANTLR code generator. Based on the rules in your grammar the ANTLR generated parser cannot disambiguate what rules to apply for a given input. You should try to refactor your grammar (see example) or you can enable backtracking for your parser (see next question).

OK, but I didn't get these warnings in oAW Xtext !

Unlike in oAW Xtext the ANTLR grammar generated by TMF Xtext doesn't have backtracking enabled by default. To enable backtracking you have to add a nested element <options backtrack="true"/> to the ANTLR generator fragments in your Xtext project's MWE workflow. For example:

  <!-- Antlr Generator fragment -->
  <fragment class="org.eclipse.xtext.generator.AntlrDelegatingFragment">
      <options backtrack="true"/>
   </fragment>

Why are generated packages from an imported grammar A duplicated in dependent grammar B ?

In addition to the import statement in B.xtext you must also configure your GenerateB.mwe workflow to let it know about the corresponding GenModels of grammar A. You do this by setting the genModels attribute of the EcoreGeneratorFragment:

   <fragment class="org.eclipse.xtext.generator.ecore.EcoreGeneratorFragment"
      genModels="platform:/resource/project/src/my/pack/SecretCompartments.genmodel"/>