We Keep Coding

Gradle Plugin dependency

What is the exact dependency I need to develop a Gradle Plugin in Java? Ideally I would like to get it from a well-known repository such as Maven Central or similar.
I have a Maven project with a core functionality and I just added two extra plugins, one for Ant, one for Maven. They are already tested and working; easy! Now, I wanted to add a third module for a Gradle plugin to make this functionality also available from any Gradle project.
However, I can't find the exact dependencies I need to develop a Gradle plugin.
The Gradle docs (such as https://docs.gradle.org/current/userguide/java_gradle_plugin.html) are not very well written to say the least. They mention:
the gradleAPI() dependency
or the java-gradle-plugin dependency
But they are quite unclear... no group, no version (really?).
If anyone can enlighten me to where I can get these dependencies from, I would be very thankful.

Gradle's public and internal APIs, aka gradleApi(), are bundled with the Gradle distribution and not independently published and therefore not easily consumable by Maven builds. There's the pending epic #1156 (Ensure plugin cross-version compatibility by allowing a user to depend on gradlePublicApi()) that might help here.
Since Gradle plugins are best to be built with Gradle, a pragmatic solution is to invoke the Gradle build from Maven and attach the produced artifact to the Maven build. Andres Almiray (aalmiray) once described this in the blog post Running Gradle Inside Maven (Web Archive Link). He describes the following high level steps:
Create a new Maven module (e.g. gradle-plugin) and add attach it to the parent POM
In the POM of gradle-plugin add a dependency to your core module. Use the maven-dependency-plugin to store dependencies to the Maven build folder, e.g. target/dependencies.
Create the build.gradle, add a Maven repository that points to target/dependencies (step 2) and let it depend on the core module as well as gradleApi(). Implement the Gradle plugin.
Use the exec-maven-plugin to invoke the Gradle build.
Use the maven-resources-plugin to copy the Gradle built plugin jars to the standard Maven build folder.
Use the build-helper-maven-plugin to attach the copied jars to the Maven build.
Sample project to be found here (gradle-in-maven).

https://docs.gradle.org/current/userguide/custom_plugins.html#sec:custom_plugins_standalone_project
In here it is mentioned that it is gradleApi() and I know that this works (from experience). The localGroovy() on that page is only needed if your plugin code uses groovy (does not apply if you only use groovy in the build.gradle of your plugin).
java-gradle-plugin is a library that makes it a bit simpler to make plugins, it is not required though. I personally prefer using gradleApi only.
EDIT:
It appears I've misunderstood the question. Here are the steps to get gradleApi jar:
Create a Gradle project with your desired Gradle version.
Add implementation gradleApi() dependency.
Import/run the project once.
Go to your .gradle folder (located in home folder in Linux-based operating systems).
Open caches folder
Open the version folder you want, e.g. 6.0.1
Open generated-gradle-jars folder.
Copy the jar to wherever you want and use it.
For me the 6.0.1 jar is at ~/.gradle/caches/6.0.1/generated-gradle-jars/gradle-api-6.0.1.jar
Please note that I have not tested this, I know the jar is there but I haven't tried using it.

Do the dependencies in build.gradle generated automatically?

Does gradle work like go mod ? First importing some dependencies in java file such as import org.apache.hadoop.mapreduce.Mapper, then calling gradle build and gradle would generate dependencies in build.gradle automatically, also download all the jars needed to gradle cache.
Or, all the denpendencies we need must add to build.gradle manully? Which version should append to the denpendency, search in the maven repo one by one?
Thank~

Gradle uses the dependencies declared in the build file to create the compile classpath. Similarly it will use test dependencies for the test compile classpath and the test runtime classpath.
So you have to declare the dependencies first, including figuring out which version you want to use in your project, and then you will be able to compile and run code that leverages these libraries.

How to fix warning about "dependency is ignored for debug..."

I have java module, that used not only for android projects, but also for java projects. Java module used json, so it has dependency:
compile 'org.json:json:20160810'
Of couse, on build android project I has warning:
WARNING: Dependency org.json:json:20160810 is ignored for debug as it
may be conflicting with the internal version provided by Android.
In case of problem, please repackage with jarjar to change the class packages
I'm use module with sources, not as jar and I do not want install module to local repository.
How I can fix issue with warning?
I know, that for jar I can use exclude group/module, but it do not work for module.

Gradle (Android) - Multiproject dependency missing in testCompile

I have a Library project A and another Library Project B. The project B imports as a compile dependency the project A and I wanted also to add this same dependency for the unit tests, so I can mock some classes from project A (not importing the test folder, but the actual project).
Even with gradle sync working properly, and ./gradlew projectB:dependencies showing the tree with the correct dependencies, in my test classes in project B I cannot access the classes from the A project.
dependencies {
//Project B dependencies
compile project(":projectA")
testCompile project(":projectA")
}
Which is even more fun is that if instead of using the project(":projectA") aka DefaultProjectDependency I use the "group:artifact:version" way aka DefaultExternalModuleDependency by installing Project A locally, it works properly.
For me it sounds like a bug, not sure if it is an Android one or a gradle one.
Versions:
gradle - 2.11
android gradle plugin - 1.5.0
Also opened an issue in b.android: https://code.google.com/p/android/issues/detail?id=201820&thanks=201820&ts=1456399375

Finally this was an error in the Android Plugin and according to the comments in this bug report it will be fixed in 2.0.0 beta 7.

Gradle transitive dependency to JAR inside of a library module

I'm migrating an Android multi-module project from Ant to Gradle.
We have some jars in the repo in the libs directory of a library module.
The dependency is as follows:
AppModule depends on LibModule.
The code in AppModule cannot access contents of the library jar that is in LibModule.
Although it can access from-source classes of LibModule (proving that the dependency in general is established).
Gradle documentation says, that all dependencies are transitive by default, but this experience seems to invalidate such claim. Is this a bug or is there some legitimate reason?
I've managed to hack it by adding a workaround dependency in AppModule:
compile fileTree(dir: '../LibModule/libs', include: ['*.jar']) // HACK!
But there should be a more DRY way to do this, right?
Gradle version: 2.1.
Interestingly, Android Studio appears to respect the transitiveness of the jar and does not signal an error.
The error occurs when I'm building using
./gradlew assembleDebug
Thy typical java error is signalled:
error: package net.jcip.annotations does not exist
import net.jcip.annotations.NotThreadSafe;
^
I know I can also specify deps in a maven-ish style, but we would like to be able to work with jars-in-the-repo as well, for our purposes.
TIA, Karol