如何声明gradle Antlr任务输出规范以避免不必要的重新构建

Question

我有一个典型的Antlr4.5项目，其中包含两个语法文件: MyLexer.g4和MyParser.g4。Antlr从中生成6个输出文件: MyLexer.java、MyLexer.tokens、MyParser.java、MyParser.tokens、MyParserBaseListener.java和MyParserListener.java。gradle任务都正常工作，因此输出文件都是按照预期生成、编译和测试的。

问题是gradle认为6个目标文件总是过时的，所以每个运行或调试会话都必须重新生成它们，因此即使没有源文件更改，也必须重新编译主java项目。

生成文件的gradle任务将输出规范定义为生成6个输出文件的文件夹。我想我需要一种方法将它定义为6个特定的文件，而不是输出文件夹。我只是不知道这样做的语法。

下面是我的build.gradle文件的相关部分：

ext.antlr4 = [
    antlrSource:    "src/main/antlr",
    destinationDir: "src/main/java/com/myantlrquestion/core/antlr/generated",
    grammarpackage:               "com.myantlrquestion.core.antlr.generated"
]

task makeAntlrOutputDir << {
    file(antlr4.destinationDir).mkdirs()
}

task compileAntlrGrammars(type: JavaExec, dependsOn: makeAntlrOutputDir) {
    // Grammars are conveniently sorted alphabetically. I assume that will remain true.
    // That ensures that files named *Lexer.g4 are listed and therefore processed before the corresponding *Parser.g4
    // It matters because the Lexer must be processed first since the Parser needs the .tokens file from the Lexer.
    // Also note that the output file naming convention for combined grammars is slightly different from separate Lexer and Parser grammars.
    def grammars = fileTree(antlr4.antlrSource).include('**/*.g4')
    def target = file("${antlr4.destinationDir}")
    inputs.files grammars
    // TODO: This output spec is incorrect, so this task is never considered up to date.
    // TODO: Tweak the outputs collection so it is correct with combined grammars as well as separate Lexer and Parser grammars.
    outputs.dir target

    main = 'org.antlr.v4.Tool'
    classpath = configurations.antlr4
    // Antlr command line args are at https://theantlrguy.atlassian.net/wiki/display/ANTLR4/ANTLR+Tool+Command+Line+Options
    args = ["-o", target,
            "-lib", target,
            //"-listener",      //"-listener" is the default
            //"-no-visitor",    //"-no-visitor" is the default
            "-package", antlr4.grammarpackage,
            grammars.files 
    ].flatten()

    // include optional description and group (shown by ./gradlew tasks command)
    description = 'Generates Java sources from ANTLR4 grammars.'
    group       = 'Build'
}

compileJava {
    dependsOn compileAntlrGrammars
    // this next line isn't technically needed unless the antlr4.destinationDir is not under buildDir, but it doesn't hurt either
    source antlr4.destinationDir
}

task cleanAntlr {
    delete antlr4.destinationDir
}
clean.dependsOn cleanAntlr

Answer 1

我发现问题并不在于目标文件过期，而是由于cleanAntlr任务中的一个错误，每次运行任何gradle任务时，它们都会被删除。问题是cleanAntlr中的所有代码都在gradle的初始化和配置阶段运行，即使cleanAntlr任务本身没有执行。

最初，该任务被定义为：

task cleanAntlr {
    delete antlr4.destinationDir
}
clean.dependsOn cleanAntlr

解决方案是这样定义它：(注意任务名称后面的"<<“。)

task cleanAntlr << {
    delete antlr4.destinationDir
}
clean.dependsOn cleanAntlr

..。或者，为了更清楚起见，可以使用这个更详细但功能相同的任务定义：

task cleanAntlr {
    doLast() {
        // Be sure to wrap the execution phase code inside doLast(). 
        // Otherwise it will run during the initialization or configuration phase, even when an unrelated task is is run.
        // It would also run when the NetBeas IDE first loaded the project.
        //println 'Deleting Antlr Directory: ' + antlr4.destinationDir
        delete antlr4.destinationDir
    }
}
clean.dependsOn cleanAntlr

修复了这个错误之后，compileAntlrGrammars任务的原始输出规范就可以正常工作了。不需要指定每个单独的输出文件。这在https://gradle.org/docs/current/userguide/more_about_tasks.html的15.9.2小节中有很好的解释。

def grammars = fileTree(antlr4.antlrSource).include('**/*.g4')
def target = file("${antlr4.destinationDir}")
inputs.files grammars
outputs.dir target

Answer 2

你能不能试试下面这段代码：

generatedFiles = ['MyLexer.java',] // and so on..
generatedFiles.each { f -> outputs.file("$target/$f") }