3. Grammar and Parser

In order for the IntelliJ Platform to parse a Simple Language file, tokens and elements must be defined based on IElementType. The Simple Language grammar must also be defined to generate a parser.

Define a Token Type

Create SimpleTokenType in the org.intellij.sdk.language.psi package by subclassing IElementType.

public class SimpleTokenType extends IElementType {

  public SimpleTokenType(@NotNull @NonNls String debugName) {
    super(debugName, SimpleLanguage.INSTANCE);
  }

  @Override
  public String toString() {
    return "SimpleTokenType." + super.toString();
  }

}

Define an Element Type

Create the SimpleElementType in the org.intellij.sdk.language.psi package by subclassing IElementType.

public class SimpleElementType extends IElementType {

  public SimpleElementType(@NotNull @NonNls String debugName) {
    super(debugName, SimpleLanguage.INSTANCE);
  }

}

Define the Grammar

Define a grammar for the Simple Language in the org/intellij/sdk/language/Simple.bnf file.

{
  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"
}

simpleFile ::= item_*

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

property ::= (KEY? SEPARATOR VALUE?) | KEY

Please see Grammar-Kit documentation for more details on BNF syntax.

The grammar defines the flexibility of the support for a language. The above grammar specifies that a property may have or may not have a key and value. This flexibility allows the IntelliJ Platform to recognize incorrectly defined properties and provide corresponding code analysis and quick-fixes.

Note that the SimpleTypes class in the elementTypeHolderClass attribute above specifies the name of a class that gets generated from the grammar in the scope of the Generate Parser Code action (see Generate a Parser); it doesn't exist at this point.

Generate a Parser

Now that the grammar is defined, generate a parser with PSI classes via Generate Parser Code from the context menu on the Simple.bnf file. This step generates a parser and PSI elements in the /src/main/gen folder of the project.

Add Generated Sources Root

To include the sources generated into /src/main/gen, the project's sourceSets must be expanded by inserting the following line in the project's Gradle build script:

sourceSets["main"].java.srcDirs("src/main/gen")

sourceSets.main.java.srcDirs 'src/main/gen'

Reload the Gradle project for changes to take effect and build the project.

Last modified: 27 February 2023