6. PSI Helpers and Utilities

Helper classes and utilities can be embedded in the code generated by Grammar-Kit.

Define Helper Methods for Generated PSI Elements

Custom methods in PSI classes are defined separately, and Grammar-Kit embeds them into generated code. Define a utility class with these helper methods:

package org.intellij.sdk.language.psi.impl;

import com.intellij.lang.ASTNode;
import org.intellij.sdk.language.psi.SimpleProperty;
import org.intellij.sdk.language.psi.SimpleTypes;

public class SimplePsiImplUtil {
  public static String getKey(SimpleProperty element) {
    ASTNode keyNode = element.getNode().findChildByType(SimpleTypes.KEY);
    if (keyNode != null) {
      // IMPORTANT: Convert embedded escaped spaces to simple spaces
      return keyNode.getText().replaceAll("\\\\ ", " ");
    } else {
      return null;
    }
  }

  public static String getValue(SimpleProperty element) {
    ASTNode valueNode = element.getNode().findChildByType(SimpleTypes.VALUE);
    if (valueNode != null) {
      return valueNode.getText();
    } else {
      return null;
    }
  }
}

The parser generates the SimpleProperty interface referenced in the code above.

Update Grammar and Regenerate the Parser

Now the utility class is added to the grammar file via the psiImplUtilClass attribute. Add methods for a particular rule to specify which one should be used for PSI classes. Compare the last line of the grammar below to the previous definition.

{
  parserClass="org.intellij.sdk.language.parser.SimpleParser"

  extends="com.intellij.extapi.psi.ASTWrapperPsiElement"

  psiClassPrefix="Simple"
  psiImplClassSuffix="Impl"
  psiPackage="org.intellij.sdk.language.psi"
  psiImplPackage="org.intellij.sdk.language.psi.impl"

  elementTypeHolderClass="org.intellij.sdk.language.psi.SimpleTypes"
  elementTypeClass="org.intellij.sdk.language.psi.SimpleElementType"
  tokenTypeClass="org.intellij.sdk.language.psi.SimpleTokenType"

  psiImplUtilClass="org.intellij.sdk.language.psi.impl.SimplePsiImplUtil"
}

simpleFile ::= item_*

private item_ ::= (property|COMMENT|CRLF)

property ::= (KEY? SEPARATOR VALUE?) | KEY {methods=[getKey getValue]}

After making changes to the grammar, regenerate the parser and PSI classes.

Define a Utility to Search Properties

Create SimpleUtil utility class to search PSI elements for defined properties over the project. This utility will be used later when implementing code completion.

Last modified: 29 九月 2022