Quick and dirty Antlr3 gradle tasks till gradle supports Antlr3 (not so proud about the distribution solution)

antlr3.gradle

//USAGE: apply from: 'antlr3.gradle'

configurations {
    antlr
}

dependencies {
    antlr    'org.antlr:antlr:3.5.2'
    compile  'org.antlr:antlr-runtime:3.5.2'
}

task distributeGrammarSourceOutput << {
    inputs.files.each { File source ->
        copy {
            from source
            into outputs.files.filter {it.name == source.name}.singleFile.parent
        }
    }
    delete inputs.files
}

task generateGrammarSource(type: JavaExec) {
    def languageName = 'antlr'
    def sourceSetName = 'main'
    def inputTree = fileTree("$project.projectDir/src/$sourceSetName/$languageName")
    def outputDir = file("$project.buildDir/generated-src/$languageName/$sourceSetName")

    inputTree.include '**/*.g'
    mkdir(outputDir)

    inputs.files inputTree
    outputs.dir outputDir
    finalizedBy distributeGrammarSourceOutput

    description = 'Generates Java sources from Antlr3 grammars.'
    main = 'org.antlr.Tool'
    classpath = configurations.antlr
    args = ["-o", outputDir, inputTree.files].flatten()

    inputTree.files.each { file ->
        def grammarFile = inputTree.dir.toPath().relativize(file.toPath())
        def grammarPrefix = grammarFile.fileName.toString()[0..-3]
        ['Lexer.java', 'Parser.java', '.tokens'].each { suffix ->
            distributeGrammarSourceOutput.inputs.file "$outputDir/$grammarPrefix$suffix"
            distributeGrammarSourceOutput.outputs.file "$outputDir/$grammarFile.parent/$grammarPrefix$suffix"
        }
    }
}

task generateTestGrammarSource(type: JavaExec) {
    def languageName = 'antlr'
    def sourceSetName = 'test'
    def inputTree = fileTree("$project.projectDir/src/$sourceSetName/$languageName")
    def outputDir = file("$project.buildDir/generated-src/$languageName/$sourceSetName")

    inputTree.include '**/*.g'
    mkdir(outputDir)

    inputs.files inputTree
    outputs.dir outputDir
    finalizedBy distributeGrammarSourceOutput

    description = 'Generates Java sources from Antlr3 grammars.'
    main = 'org.antlr.Tool'
    classpath = configurations.antlr
    args = ["-o", outputDir, inputTree.files].flatten()

    inputTree.files.each { file ->
        def grammarFile = inputTree.dir.toPath().relativize(file.toPath())
        def grammarPrefix = grammarFile.fileName.toString()[0..-3]
        ['Lexer.java', 'Parser.java', '.tokens'].each { suffix ->
            distributeGrammarSourceOutput.inputs.file "$outputDir/$grammarPrefix$suffix"
            distributeGrammarSourceOutput.outputs.file "$outputDir/$grammarFile.parent/$grammarPrefix$suffix"
        }
    }
}

sourceSets.main.java.srcDir  generateGrammarSource.outputs.files.singleFile
sourceSets.test.java.srcDir  generateTestGrammarSource.outputs.files.singleFile

compileJava.dependsOn        generateGrammarSource
compileTestJava.dependsOn    generateTestGrammarSource