I am currently migrating my project from Groovy to Kotlin DSL, and as it is multi-module, I have chosen to use Convention Plugins.

The problem is that the minSdk is not being applied correctly. I have two main modules, one for the mobile and tablet app and one for wear. In the app module I use the following plugin:

u/Suppress("UnstableApiUsage")
class ApplicationsConventionPlugin : Plugin<Project> {

    override fun apply(target: Project) {
        with(target) {
            with(pluginManager) {
                apply("com.android.application")
                apply("org.jetbrains.kotlin.android")
            }

            extensions.configure<ApplicationExtension> {
                configureKotlinAndroid(commonExtension = this)

                defaultConfig {

                    versionCode = APP_VERSION_CODE
                    versionName = VERSION_NAME
                    targetSdk = APP_TARGET_SDK_VERSION

                    buildFeatures {
                        buildConfig = true
                        viewBinding = true
                    }
                }

                buildTypes {
                    AndroidBuildType.values().forEach {
                        maybeCreate(it.name).apply {
                            it.initWith?.let {
                                initWith(getByName(name))
                            }

                            applicationIdSuffix = it.applicationSuffixId
                            isDefault = it.isDefault
                            isDebuggable = it.isDebuggable
                            isMinifyEnabled = it.isMinifyEnabled
                            isShrinkResources = it.isShrinkResources
                        }
                    }
                }

                testOptions {
                    unitTests {
                        isIncludeAndroidResources = true
                        isReturnDefaultValues = true
                    }
                    animationsDisabled = true
                }
            }
        }
    }
}

And for the wear module, I use the following plugin:

@Suppress("UnstableApiUsage")
class WearableApplicationsConventionPlugin : Plugin<Project> {

    override fun apply(target: Project) {
        with(target) {
            with(pluginManager) {
                apply("com.android.application")
                apply("org.jetbrains.kotlin.android")
            }

            extensions.configure<ApplicationExtension> {
                configureWearableKotlinAndroid(commonExtension = this)

                defaultConfig {

                    versionCode = WEARABLE_VERSION_CODE
                    versionName = VERSION_NAME
                    targetSdk = WEARABLE_TARGET_SDK_VERSION

                    buildFeatures {
                        buildConfig = true
                        viewBinding = true
                    }
                }

                buildTypes {
                    AndroidBuildType.values().forEach {
                        maybeCreate(it.name).apply {
                            it.initWith?.let {
                                initWith(getByName(name))
                            }

                            applicationIdSuffix = it.applicationSuffixId
                            isDefault = it.isDefault
                            isDebuggable = it.isDebuggable
                            isMinifyEnabled = it.isMinifyEnabled
                            isShrinkResources = it.isShrinkResources
                        }
                    }
                }

                testOptions {
                    unitTests {
                        isIncludeAndroidResources = true
                        isReturnDefaultValues = true
                    }
                    animationsDisabled = true
                }
            }
        }
    }
}

Both plugins have a very similar method which is configureKotlinAndroid and configureWearableKotlinAndroid, in which, as I saw in the repository of NowInAndroid, within the defaultConfig block, apply the minSdk, where in my case, I apply on one side a minSdk of 26 for app and a minSdk of 30 for Wear OS, since a lower version I can not put in Wear OS.

internal fun Project.configureKotlinAndroid(
    commonExtension: CommonExtension<*, *, *, *, *, *>,
) {
    commonExtension.apply {
        compileSdk = COMPILE_SDK_VERSION
        
        defaultConfig { 
            minSdk = 26
        }

        compileOptions {
            sourceCompatibility = JavaVersion.VERSION_17
            targetCompatibility = JavaVersion.VERSION_17
        }

        lint {
            abortOnError = true
        }
    }

    configureKotlin<KotlinAndroidProjectExtension>()
}

internal fun Project.configureWearableKotlinAndroid(
    commonExtension: CommonExtension<*, *, *, *, *, *>,
) {
    commonExtension.apply {
        compileSdk = COMPILE_SDK_VERSION
        
        defaultConfig { 
            minSdk = 30
        }

        compileOptions {
            sourceCompatibility = JavaVersion.VERSION_17
            targetCompatibility = JavaVersion.VERSION_17
        }

        lint {
            abortOnError = true
        }
    }

    configureKotlin<KotlinAndroidProjectExtension>()
}

The problem is that when I'm trying to compile the project I'm finding that the minSdk is not being applied properly because Wear OS modules are failing due to the fact that the libraries require a minSdk of 30 and I'm using 26, so instead of taking the wear module it's taking the app one.

Here I have two questions, the first one: if I'm compiling the app module, why does it also compile the wearable one?

And, why doesn't it work if I have specified the minSdk to 30 in Wear OS? Also, if I put the minSdk directly in the app build.gradle.kts file and in the wearable build.gradle.kts file, so it works, what's different?