[Gradle][MPP] Implement InternalKotlinSourceSet.compilations

This property can later be used to replace the slow
compilationsBySourceSet util.

KT-52726

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/AbstractCompilationDetails.kt

@@ -32,6 +32,7 @@ abstract class AbstractCompilationDetails<T : KotlinCommonOptions> : Compilation
         directlyIncludedKotlinSourceSetsImpl.add(sourceSet)
         sourceSet.internal.withDependsOnClosure.forAll { withDependsOn ->
             kotlinSourceSetsClosureImpl.add(withDependsOn)
+            withDependsOn.internal.addCompilation(compilation)
         }
 
         whenSourceSetAdded(sourceSet)

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/sources/AbstractKotlinSourceSet.kt

@@ -7,6 +7,7 @@
 
 package org.jetbrains.kotlin.gradle.plugin.sources
 
+import org.jetbrains.kotlin.gradle.plugin.KotlinCompilation
 import org.jetbrains.kotlin.gradle.plugin.KotlinSourceSet
 import org.jetbrains.kotlin.gradle.utils.MutableObservableSet
 import org.jetbrains.kotlin.gradle.utils.ObservableSet
@@ -15,6 +16,7 @@ abstract class AbstractKotlinSourceSet : InternalKotlinSourceSet {
     private val dependsOnImpl = MutableObservableSet<KotlinSourceSet>()
     private val dependsOnClosureImpl = MutableObservableSet<KotlinSourceSet>()
     private val withDependsOnClosureImpl = MutableObservableSet<KotlinSourceSet>(this)
+    private val compilationsImpl = MutableObservableSet<KotlinCompilation<*>>()
 
     final override val dependsOn: ObservableSet<KotlinSourceSet>
         get() = dependsOnImpl
@@ -25,6 +27,9 @@ abstract class AbstractKotlinSourceSet : InternalKotlinSourceSet {
     final override val withDependsOnClosure: ObservableSet<KotlinSourceSet>
         get() = withDependsOnClosureImpl
 
+    override val compilations: ObservableSet<KotlinCompilation<*>>
+        get() = compilationsImpl
+
     final override fun dependsOn(other: KotlinSourceSet) {
         if (other == this) return
         /*
@@ -46,5 +51,9 @@ abstract class AbstractKotlinSourceSet : InternalKotlinSourceSet {
     }
 
     protected open fun afterDependsOnAdded(other: KotlinSourceSet) = Unit
+
+    final override fun addCompilation(compilation: KotlinCompilation<*>) {
+        compilationsImpl.add(compilation)
+    }
 }
 

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/sources/InternalKotlinSourceSet.kt

@@ -5,6 +5,7 @@
 
 package org.jetbrains.kotlin.gradle.plugin.sources
 
+import org.jetbrains.kotlin.gradle.plugin.KotlinCompilation
 import org.jetbrains.kotlin.gradle.plugin.KotlinSourceSet
 import org.jetbrains.kotlin.gradle.utils.ObservableSet
 
@@ -17,4 +18,6 @@ internal interface InternalKotlinSourceSet : KotlinSourceSet {
     override val dependsOn: ObservableSet<KotlinSourceSet>
     val dependsOnClosure: ObservableSet<KotlinSourceSet>
     val withDependsOnClosure: ObservableSet<KotlinSourceSet>
+    val compilations: ObservableSet<KotlinCompilation<*>>
+    fun addCompilation(compilation: KotlinCompilation<*>)
 }