How to get dependencies from a gradle plugin using “api” or “implementation” directives

Question

Background: Running Android Studio 3.0-beta7 and trying to get a javadoc task to work for an Android library (the fact that this is not available as a ready-made task in the first place is really strange), and I managed to tweak an answer to a different question for my needs, ending up with this code (https://stackoverflow.com/a/46810617/1226020):

task javadoc(type: Javadoc) {
    failOnError false
    source = android.sourceSets.main.java.srcDirs
    // Also add the generated R class to avoid errors...
    // TODO: debug is hard-coded
    source += "$buildDir/generated/source/r/debug/"
    // ... but exclude the R classes from the docs
    excludes += "**/R.java"

    // TODO: "compile" is deprecated in Gradle 4.1, 
    // but "implementation" and "api" are not resolvable :(
    classpath += configurations.compile

    afterEvaluate {
        // Wait after evaluation to add the android classpath
        // to avoid "buildToolsVersion is not specified" error
        classpath += files(android.getBootClasspath())

        // Process AAR dependencies
        def aarDependencies = classpath.filter { it.name.endsWith('.aar') }
        classpath -= aarDependencies
        aarDependencies.each { aar ->
            System.out.println("Adding classpath for aar: " + aar.name)
            // Extract classes.jar from the AAR dependency, and add it to the javadoc classpath
            def outputPath = "$buildDir/tmp/exploded-aar/${aar.name.replace('.aar', '.jar')}"
            classpath += files(outputPath)

            // Use a task so the actual extraction only happens before the javadoc task is run
            dependsOn task(name: "extract ${aar.name}").doLast {
                extractEntry(aar, 'classes.jar', outputPath)
            }
        }
    }
}

// Utility method to extract only one entry in a zip file
private def extractEntry(archive, entryPath, outputPath) {
    if (!archive.exists()) {
        throw new GradleException("archive $archive not found")
    }

    def zip = new java.util.zip.ZipFile(archive)

    zip.entries().each {
        if (it.name == entryPath) {
            def path = new File(outputPath)

            if (!path.exists()) {
                path.getParentFile().mkdirs()

                // Surely there's a simpler is->os utility except
                // the one in java.nio.Files? Ah well...
                def buf = new byte[1024]
                def is = zip.getInputStream(it)
                def os = new FileOutputStream(path)
                def len

                while ((len = is.read(buf)) != -1) {
                    os.write(buf, 0, len)
                }
                os.close()
            }
        }
    }
    zip.close()
}

This code tries to find all dependency AAR:s, loops through them and extracts classes.jar from them, and puts them in a temp folder that is added to the classpath during javadoc generation. Basically trying to reproduce what the really old android gradle plugin used to do with "exploded-aar".

However, the code relies on using compile dependencies. Using api or implementation that are recommended with Gradle 4.1 will not work, since these are not resolvable from a Gradle task.

Question: how can I get a list of dependencies using the api or implementation directives when e.g. configuration.api renders a "not resolvable" error?

Bonus question: is there a new, better way to create javadocs for a library with Android Studio 3.0 that doesn't involve 100 lines of workarounds?

Answer 1

You can wait for this to be merged:

https://issues.apache.org/jira/browse/MJAVADOC-450

Basically, the current Maven Javadoc plugin ignores classifiers such as AAR.