CODEWITHSUNDEEP
javagradledependenciesantlr
David
David

Reputation: 361

How do I declare gradle Antlr task output specs to avoid unnecessary rebuilds

I have a typical Antlr 4.5 project with two grammar files: MyLexer.g4 and MyParser.g4. From them, Antlr generates 6 output files: MyLexer.java, MyLexer.tokens, MyParser.java, MyParser.tokens, MyParserBaseListener.java and MyParserListener.java. The gradle tasks are all working correctly so that the output files are all generated, compiled and tested as expected.

The problem is that gradle sees the 6 target files as always being out of date, so every run or debug session has to regenerate them and therefore has to recompile the main java project even if none of the source files have changed.

The gradle task which generates the file has the output spec defined as the folder into which the 6 output files are generated. I think that I need a way to define it as being the 6 specific files rather than the output folder. I just don't know the syntax to do that.

Here's the pertinent part of my build.gradle file:

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

Upvotes: 1

Views: 1130

Answers (2)

David
David

Reputation: 361

I discovered the problem was not that the target files were out of date, but rather, due to a bug in the cleanAntlr task, they were being deleted every time that any gradle task was run. The problem was that all of the code in cleanAntlr was being run during gradle's initialization and configuration phase, even if the cleanAntlr task itself wasn't being executed.

Originally, the task was defined as:

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

The solution was to define it like this: (Note the "<<" after the task name.)

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

... or, for additional clarity, use this more verbose, but functionally equivalent task definition:

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

With that bug fixed, the original outputs specification for the compileAntlrGrammars task works correctly. There is no need to specify each individual output file. This is explained quite well in section 15.9.2 of https://gradle.org/docs/current/userguide/more_about_tasks.html.

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

Upvotes: 1

Opal
Opal

Reputation: 84904

Could you please try the following piece of code:

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

Upvotes: 0

Related Questions