Provide completion from my language to another

The easiest way is to implement getVariants in your reference and return LookupElement[] from it.
If your completion might take a long time or you need some advanced stuff, you can implement CompletionContributor. Its Javadoc contains the necessary details.

Hi Peter,
Thank you wery much! I thought that contibutor can be only used inside your own custom language, because when it defiened in plugin.xml it also has "language" tag. But I found that language can be specified as "any":

<completion.contributor language="any" ... />

I also want to ask, why literal.getValue returns something like: "yourtextIntellijIdeaRulezzzzzz" in that place:

      new CompletionProvider[CompletionParameters]() {
        def addCompletions(parameters: CompletionParameters, context: ProcessingContext, resultSet: CompletionResultSet) {
            parameters.getPosition.getContext match {
              case literal: PsiLiteral if literal.getValue.isInstanceOf[String] =>
                println(literal.getValue)
              case _ => //just ignore
            }
        }
      }

, but at the same time this code inside ReferenceContributor during tha call of literal.getValue returns normal value without "IntellijIdeaRulezzzzzz":

    registrar.registerReferenceProvider(PlatformPatterns.psiElement(classOf[PsiLiteral]), new PsiReferenceProvider() {
      def getReferencesByElement(element: PsiElement, context: ProcessingContext) = {
        val literal = element.asInstanceOf[PsiLiteral]
        literal.getValue match {
          case text: String =>
            if (text != null && text.endsWith(".table")) {
              Array[PsiReference](new XrlDecideReference(element, new TextRange(1, text.length() - ".table".length + 1), "table"))
            } else Array[PsiReference]()
          case _ => Array[PsiReference]()
        }
      }
    })

Oh, I understood. Instead of using

parameters.getPosition.getContext.getValue

it should be used

parameters.getOriginalPosition.getContext.getValue

Thanks again!

Actually, using originalPosition won't probably always function as you imagine it to. This rulezzz thing is a dummy identifier inserted to make writing completion easier for you. See again the javadoc on CompletionContributor, search by keyword "dummy identifier".

I see. Thanks)