gradle submodules of submodules not built with :submodule:build syntax - gradle

Question

I have the following project structure correctly found by gradle:
$ ./gradlew projects
Root project 'test-project'
\--- Project ':sub-1'
\--- Project ':sub-1:sub-2'
Which makes me believe that my setups is correct.
Now, I have found that the following gradle syntax:
$ ./gradlew clean :sub-1:build
is not equivalent to:
$ cd sub-1
$ ../gradlew clean build
$ cd ..
The above is equivalence is stated in many places on the gradle website.
Like HERE
Running the former, the result is incorrect:
> Task :sub-1:test
test.project.LibrarySuite > someLibraryMethod is always true PASSED
Running the latter, the result is correct:
> Task :sub-1:test
test.project.LibrarySuite > someLibraryMethod is always true PASSED
> Task :sub-1:sub-2:test
test.project.LibrarySuite > someLibraryMethod is always true PASSED
Please help me understand if I might have assumed or done anything wrong, or if it's a bug that should be raised to the gradle team.

Answer 1

You will find detailed description of how Gradle handles execution of tasks in a multiproject build setup here : https://docs.gradle.org/current/userguide/intro_multi_project_builds.html#sec:executing_a_multiproject_build , specially:
From a user’s perspective, multi-project builds are still collections
of tasks you can run. The difference is that you may want to control
which project’s tasks get executed. You have two options here:
Change to the directory corresponding to the subproject you’re
interested in and just execute gradle as normal.
Use a qualified task name from any directory, although this is usually
done from the root. For example: gradle :services:webservice:build
will build the webservice subproject and any subprojects it depends
on.
The first approach is similar to the single-project use case, but
Gradle works slightly differently in the case of a multi-project
build. The command gradle test will execute the test task in any
subprojects, relative to the current working directory, that have that
task. So if you run the command from the root project directory,
you’ll run test in api, shared, services:shared and
services:webservice. If you run the command from the services project
directory, you’ll only execute the task in services:shared and
services:webservice.
This explains how Gradle behaves in the two examples you gave in your question :
$ ./gradlew clean :sub-1:build
from the root project directory: you execute task clean, which will be executed for current project and each subprojects below, then :sub-1:build (with qualified task name) which executes build tasks ONLY for subproject sub1
Gradle execution log:
> Task :clean UP-TO-DATE
> Task :sub-1:clean
> Task :sub-1:sub-2:clean UP-TO-DATE
> Task :sub-1:compileJava NO-SOURCE
> Task :sub-1:processResources NO-SOURCE
> Task :sub-1:classes UP-TO-DATE
> Task :sub-1:jar
> Task :sub-1:assemble
> Task :sub-1:compileTestJava NO-SOURCE
> Task :sub-1:processTestResources NO-SOURCE
> Task :sub-1:testClasses UP-TO-DATE
> Task :sub-1:test NO-SOURCE
> Task :sub-1:check UP-TO-DATE
> Task :sub-1:build
EDIT to answer #Guido's comment: this will also build any other projects sub-1 depends on, so ./gradlew clean :sub-1:build will also trigger build of sub-2 if sub-1 project dependsOn sub-2:
sub-1 build.gradle
dependencies {
implementation project(":sub-1:sub-2")
}
$ cd sub-1 && ../gradlew clean build
From sub-1 subproject directory , you trigger tasks clean then build, without using qualified names, so these two tasks will both be executed on current project and sub-projects` :
Gralde output:
$ ../gradlew clean build --console=plain
> Task :sub-1:clean
> Task :sub-1:sub-2:clean
> Task :sub-1:compileJava NO-SOURCE
> Task :sub-1:processResources NO-SOURCE
> Task :sub-1:classes UP-TO-DATE
> Task :sub-1:jar
> Task :sub-1:assemble
> Task :sub-1:compileTestJava NO-SOURCE
> Task :sub-1:processTestResources NO-SOURCE
> Task :sub-1:testClasses UP-TO-DATE
> Task :sub-1:test NO-SOURCE
> Task :sub-1:check UP-TO-DATE
> Task :sub-1:build
> Task :sub-1:sub-2:compileJava NO-SOURCE
> Task :sub-1:sub-2:processResources NO-SOURCE
> Task :sub-1:sub-2:classes UP-TO-DATE
> Task :sub-1:sub-2:jar
> Task :sub-1:sub-2:assemble
> Task :sub-1:sub-2:compileTestJava NO-SOURCE
> Task :sub-1:sub-2:processTestResources NO-SOURCE
> Task :sub-1:sub-2:testClasses UP-TO-DATE
> Task :sub-1:sub-2:test NO-SOURCE
> Task :sub-1:sub-2:check UP-TO-DATE
> Task :sub-1:sub-2:build