When applying any KotlinTargetHierarchyDescriptor (e.g. by calling targetHierarchy.default()), the descriptor will be applied on individual compilations, creating multiple trees of shared SourceSets.

The name of given shared source set within the target hierarchy will be built by lowerCamelCase(nameOfGroup, nameOfSourceSetTree) So for the 'common' group within the 'main' tree the shared SourceSet name will be 'commonMain'

The most default case will create two well known SourceSetTrees:

• The main tree with commonMain as its root SourceSet

• The test tree with commonTest as its root SourceSet

e.g.

kotlin {
    targetHierarchy.default()
    jvm()
    iosX64()
    iosArm64()
}

will create two SourceSetTrees: "main" and "test"

                       "main"                               "test"

                     commonMain                           commonTest
                         |                                    |
                         |                                    |
              +----------+----------+              +----------+----------+
              |                     |              |                     |
             ...                  jvmMain         ...                  jvmTest
              |                                    |
              |                                    |
            iosMain                              iosTest
              |                                    |
         +----+-----+                         +----+-----+
         |          |                         |          |
    iosX64Main   iosArm64Main            iosX64Test   iosArm64Test

Usually, the name of the compilation correlates to the name of the SourceSetTree: As seen in the previous example, the "main" tree under the "commonMain" root contains all 'main' compilations of the projects targets. The "test" tree under the "commonTest" root contains all 'test' compilations of the projects targets.

There are some exceptions, where the name of the compilations cannot be chosen by the user directly (Android) In this case, the name of the SourceSet can be configured outside the target hierarchy DSL.