IntelliJ Platform SDK DevGuide

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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.

Reference: Implementing a Parser and PSI

3.1. Define a Token Type

Create SimpleTokenType in the org.intellij.sdk.language.psi package (see the simple_language_plugin code sample) by subclassing IElementType.

// Copyright 2000-2020 JetBrains s.r.o. and other contributors. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file. package org.intellij.sdk.language.psi; import com.intellij.psi.tree.IElementType; import org.intellij.sdk.language.SimpleLanguage; import org.jetbrains.annotations.NonNls; import org.jetbrains.annotations.NotNull; public class SimpleTokenType extends IElementType { public SimpleTokenType(@NotNull @NonNls String debugName) { super(debugName, SimpleLanguage.INSTANCE); } @Override public String toString() { return "SimpleTokenType." + super.toString(); } }

3.2. Define an Element Type

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

// Copyright 2000-2020 JetBrains s.r.o. and other contributors. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file. package org.intellij.sdk.language.psi; import com.intellij.psi.tree.IElementType; import org.intellij.sdk.language.SimpleLanguage; import org.jetbrains.annotations.NonNls; import org.jetbrains.annotations.NotNull; public class SimpleElementType extends IElementType { public SimpleElementType(@NotNull @NonNls String debugName) { super(debugName, SimpleLanguage.INSTANCE); } }

3.3. Define the Grammar

Define a grammar for the Simple Language in the com/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" psiImplUtilClass="org.intellij.sdk.language.psi.impl.SimplePsiImplUtil" } simpleFile ::= item_* private item_ ::= (property|COMMENT|CRLF) property ::= (KEY? SEPARATOR VALUE?) | KEY

As shown, a properties file can contain properties, comments, and line breaks.

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 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 field above specifies the name of a class that gets generated from the grammar; it doesn’t exist at this point.

3.4. 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. Mark this folder as Generated Sources Root and make sure everything compiles without errors.

Parser

Last modified: 21 September 2020