# Chapter 56. The ANTLR Plugin

The ANTLR plugin extends the Java plugin to add support for generating parsers using ANTLR.

The ANTLR plugin supports ANTLR version 2, 3 and 4.

## 56.1. Usage

To use the ANTLR plugin, include the following in your build script:

Example 56.1. Using the ANTLR plugin

`build.gradle`

    apply plugin: 'antlr'

## 56.2. Tasks

The ANTLR plugin adds a number of tasks to your project, as shown below.

Table 56.1. ANTLR plugin - tasks

Task name | Depends on | Type | Description
`generateGrammarSource` | - | `AntlrTask` | Generates the source files for all production ANTLR grammars.
`generateTestGrammarSource` | - | `AntlrTask` | Generates the source files for all test ANTLR grammars.
`generate`SourceSet`GrammarSource` | - | `AntlrTask` | Generates the source files for all ANTLR grammars for the given source set.

The ANTLR plugin adds the following dependencies to tasks added by the Java plugin.

Table 56.2. ANTLR plugin - additional task dependencies

Task name | Depends on
compileJava | generateGrammarSource
compileTestJava | generateTestGrammarSource
compile`SourceSet`Java | generate`SourceSet`GrammarSource

## 56.3. Project layout

Table 56.3. ANTLR plugin - project layout

Directory | Meaning
`src/main/antlr` | Production ANTLR grammar files. If the ANTLR grammar is organized in packages, the structure in the antlr folder should reflect the package structure. This ensures that the generated sources end up in the correct target subfolder.
`src/test/antlr` | Test ANTLR grammar files.
`src/`sourceSet`/antlr` | ANTLR grammar files for the given source set.

## 56.4. Dependency management

The ANTLR plugin adds an `antlr` dependency configuration which provides the ANTLR implementation to use. The following example shows how to use ANTLR version 3.

Example 56.2. Declare ANTLR version

`build.gradle`

    repositories {
        mavenCentral()
    }

    dependencies {
        antlr "org.antlr:antlr:3.5.2" // use ANTLR version 3
        // antlr "org.antlr:antlr4:4.5" // use ANTLR version 4
    }

If no dependency is declared, `antlr:antlr:2.7.7` will be used as the default. To use a different ANTLR version add the appropriate dependency to the `antlr` dependency configuration as above.

## 56.5. Convention properties

The ANTLR plugin does not add any convention properties.

## 56.6. Source set properties

The ANTLR plugin adds the following properties to each source set in the project.

Table 56.4. ANTLR plugin - source set properties

Property name | Type | Default value | Description
`antlr` | `SourceDirectorySet` (read-only) | Not null | The ANTLR grammar files of this source set. Contains all `.g` or `.g4` files found in the ANTLR source directories, and excludes all other types of files.
`antlr.srcDirs` | `Set<File>`. Can set using anything described in Section 19.5, “Specifying a set of input files”. | `[`projectDir`/src/`name`/antlr]` | The source directories containing the ANTLR grammar files of this source set.

## 56.7. Controlling the ANTLR generator process

The ANTLR tool is executed in a forked process. This allows fine grained control over memory settings for the ANTLR process. To set the heap size of a ANTLR process, the `maxHeapSize` property of `AntlrTask` can be used. To pass additional command-line arguments, append to the `arguments` property of `AntlrTask`.

Example 56.3. setting custom max heap size and extra arguments for ANTLR

`build.gradle`

    generateGrammarSource {
        maxHeapSize = "64m"
        arguments += ["-visitor", "-long-messages"]
    }