So I think I've got a good (but wordy) solution for Android. At the time of writing I'm using Gradle 6.7, Android plugin 4.1.0, and AspectJ tools 1.9.6.
The gist of the problem is that:
- Java is compiled by task
compileDebugJavaWithJavac
- Kotlin is compiled by task
compileDebugKotlin
- Gradle can run either one of these tasks, or both of them, or none
compileDebugJavaWithJavac depends on compileDebugKotlin- weaving Kotlin usually requires Java classes.
If you look at these points closely, you'll see that you can't do weaving as part of compiling Kotlin, as Java classes can be missing at this point. If you do that, you'll get warnings such as:
WARN: incorrect classpath: C:\Users\user\StudioProjects\myapp\app\build\intermediates\javac\debug\classes
and errors such as
ERROR: can’t determine modifiers of missing type myapp.Foo.Bar
So the better approach would be to postpone weaving until Java classes are compiled. But as you would be modifying files not as a part of compilation task, you lose incremental builds... Besides, this postponed weaving is super hard to get right—remember, none of the compile tasks might be actually scheduled for running!
The real solution is to wrap weaving in a Transform, which will produce a Gradle task with its own inputs and outputs. This means that you will not be polluting the files of compile tasks, and those tasks, as well as this task, will be, so to say, UP-TO-DATE-able. This requires quite a bit of code, but it's rather sensible!
First, put this in your project build.gradle.kts:
buildscript {
dependencies {
classpath("org.aspectj:aspectjtools:1.9.6")
}
}
This is needed to run weaving from inside “inside” the buildscript. If you want to run weaving in a separate process, which is a good idea on Windows, you will need the path of this jar, which you can get by adding the following to your app build.gradle.kts:
val weaving: Configuration by configurations.creating
dependencies {
weaving("org.aspectj:aspectjtools:1.9.6")
}
Finally, put AspectJ runtime on the classpath (app build.gradle.kts, note that I only need weaving in debug builds):
dependencies {
debugImplementation("org.aspectj:aspectjrt:1.9.6")
}
Now, here's my setup. I have a local logging library, :cats, which containts aspects that I want to weave. Logging statements are only inside my project, and not anywhere else. Also, I only want to run these in debug builds. So here's the transformation that “weaves cats” into the app (app's build.gradle.kts):
class TransformCats : Transform() {
override fun getName(): String = TransformCats::class.simpleName!!
override fun getInputTypes() = setOf(QualifiedContent.DefaultContentType.CLASSES)
// only look for annotations in app classes
// transformation will consume these and put woven classes in the output dir
override fun getScopes() = mutableSetOf(QualifiedContent.Scope.PROJECT)
// ...but also have the rest on our class path
// these will not be touched by the transformation
override fun getReferencedScopes() = mutableSetOf(QualifiedContent.Scope.SUB_PROJECTS,
QualifiedContent.Scope.EXTERNAL_LIBRARIES)
override fun isIncremental() = false
// only run on debug builds
override fun applyToVariant(variant: VariantInfo) = variant.isDebuggable
override fun transform(invocation: TransformInvocation) {
if (!invocation.isIncremental) {
invocation.outputProvider.deleteAll()
}
val output = invocation.outputProvider.getContentLocation(name, outputTypes,
scopes, Format.DIRECTORY)
if (output.isDirectory) FileUtils.deleteDirectoryContents(output)
FileUtils.mkdirs(output)
val input = mutableListOf<File>()
val classPath = mutableListOf<File>()
val aspectPath = mutableListOf<File>()
invocation.inputs.forEach { source ->
source.directoryInputs.forEach { dir ->
input.add(dir.file)
classPath.add(dir.file)
}
source.jarInputs.forEach { jar ->
input.add(jar.file)
classPath.add(jar.file)
}
}
invocation.referencedInputs.forEach { source ->
source.directoryInputs.forEach { dir ->
classPath.add(dir.file)
}
source.jarInputs.forEach { jar ->
classPath.add(jar.file)
if (jar.name == ":cats") aspectPath.add(jar.file)
}
}
weave(classPath, aspectPath, input, output)
}
}
android.registerTransform(TransformCats())
And here's the weaving code mentioned above:
// ajc gets hold of some files such as R.jar, and on Windows it leads to errors such as:
// The process cannot access the file because it is being used by another process
// to avoid these, weave in a process, which `javaexec` will helpfully launch for us.
fun weave(classPath: Iterable<File>, aspectPath: Iterable<File>, input: Iterable<File>, output: File) {
val runInAProcess = OperatingSystem.current().isWindows
val bootClassPath = android.bootClasspath
println(if (runInAProcess) ":: weaving in a process..." else ":: weaving...")
println(":: boot class path: $bootClassPath")
println(":: class path: $classPath")
println(":: aspect path: $aspectPath")
println(":: input: $input")
println(":: output: $output")
val arguments = listOf("-showWeaveInfo",
"-1.8",
"-bootclasspath", bootClassPath.asArgument,
"-classpath", classPath.asArgument,
"-aspectpath", aspectPath.asArgument,
"-inpath", input.asArgument,
"-d", output.absolutePath)
if (runInAProcess) {
javaexec {
classpath = weaving
main = "org.aspectj.tools.ajc.Main"
args = arguments
}
} else {
val handler = MessageHandler(true)
Main().run(arguments.toTypedArray(), handler)
val log = project.logger
for (message in handler.getMessages(null, true)) {
when (message.kind) {
IMessage.DEBUG -> log.debug("DEBUG " + message.message, message.thrown)
IMessage.INFO -> log.info("INFO: " + message.message, message.thrown)
IMessage.WARNING -> log.warn("WARN: " + message.message, message.thrown)
IMessage.FAIL,
IMessage.ERROR,
IMessage.ABORT -> log.error("ERROR: " + message.message, message.thrown)
}
}
}
}
val Iterable<File>.asArgument get() = joinToString(File.pathSeparator)
(The Windows part is using weaving configuration; you may not want either part of the if)
This is it!
Edit: As of AGP 4.2.0, jar.name doesn't return anything useful. For the time being, I used this fragile workaround:
if (jar.file.directoriesInsideRootProject().contains("cats")) {
aspectPath.add(jar.file)
}
fun File.directoriesInsideRootProject() = sequence {
var file = this@directoriesInsideRootProject
while (true) {
yield(file.name)
file = file.parentFile ?: break
if (file == rootProject.projectDir) break
}
}
