[Gradle] Add dsl marker to KotlinSourceSet

We also need users to distinguish KotlinSourceSet DSL from other levels
of DSL, specifically extension one.

^KT-64722 In Progress

libraries/stdlib/build.gradle.kts

@@ -431,13 +431,15 @@ kotlin {
             kotlin.srcDir("${jsDir}/test")
         }
 
+        val commonMainSourceSet = commonMain.get()
         val nativeWasmMain by creating {
-            dependsOn(commonMain.get())
+            dependsOn(commonMainSourceSet)
             kotlin.srcDir("native-wasm/src")
         }
 
+        val commonTestSourceSet = commonTest.get()
         val nativeWasmTest by creating {
-            dependsOn(commonTest.get())
+            dependsOn(commonTestSourceSet)
             kotlin.srcDir("native-wasm/test")
         }
 
@@ -525,7 +527,7 @@ kotlin {
 
         if (kotlinBuildProperties.isInIdeaSync) {
             val nativeKotlinTestCommon by creating {
-                dependsOn(commonMain.get())
+                dependsOn(commonMainSourceSet)
                 val prepareKotlinTestCommonNativeSources by tasks.registering(Sync::class) {
                     from("../kotlin.test/common/src/main/kotlin")
                     from("../kotlin.test/annotations-common/src/main/kotlin")

libraries/tools/kotlin-gradle-plugin-api/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/KotlinSourceSet.kt

@@ -8,8 +8,10 @@ package org.jetbrains.kotlin.gradle.plugin
 import org.gradle.api.Action
 import org.gradle.api.Named
 import org.gradle.api.file.SourceDirectorySet
+import org.jetbrains.kotlin.gradle.dsl.KotlinGradlePluginDsl
 import org.jetbrains.kotlin.tooling.core.HasMutableExtras
 
+@KotlinGradlePluginDsl
 interface KotlinSourceSet : Named, HasProject, HasMutableExtras, HasKotlinDependencies {
     val kotlin: SourceDirectorySet
 

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/MppHighlightingTestDataWithGradleIT.kt

@@ -58,15 +58,25 @@ class MppHighlightingTestDataWithGradleIT : BaseGradleIT() {
         // create Gradle Kotlin source sets for project roots:
         val scriptCustomization = buildString {
             appendLine()
-            appendLine("kotlin {\n    sourceSets {")
+            appendLine("kotlin {")
+            appendLine(
+                """
+                |    fun configureTargetsDefaultDependsOn(sourceSet: org.jetbrains.kotlin.gradle.plugin.KotlinSourceSet) {
+                |        listOf(${cliCompiler.targets.joinToString { "$it()" }}).forEach { 
+                |            it.compilations["main"].defaultSourceSet.dependsOn(sourceSet) 
+                |        }
+                |    }
+                |    
+                """.trimMargin()
+            )
+            appendLine("    sourceSets {")
             sourceRoots.forEach { sourceRoot ->
                 if (sourceRoot.kotlinSourceSetName != "commonMain") {
                     appendLine(
-                        """        create("${sourceRoot.kotlinSourceSetName}") {
+                        """        
+                          |        create("${sourceRoot.kotlinSourceSetName}") {
                           |            dependsOn(getByName("commonMain"))
-                          |            listOf(${cliCompiler.targets.joinToString { "$it()" }}).forEach { 
-                          |                it.compilations["main"].defaultSourceSet.dependsOn(this@create) 
-                          |            }
+                          |            configureTargetsDefaultDependsOn(this@create) 
                           |        }
                           |    
                         """.trimMargin()
@@ -85,7 +95,8 @@ class MppHighlightingTestDataWithGradleIT : BaseGradleIT() {
                     }
                 }
             }
-            appendLine("    }\n}")
+            appendLine("    }")
+            appendLine("}")
         }
 
         gradleBuildScript().appendText("\n" + scriptCustomization)

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/native-download-maven/build.gradle.kts

@@ -10,8 +10,9 @@ repositories {
 }
 
 kotlin {
+    val commonMainSourceSet = sourceSets.commonMain.get()
     val nativeMain by sourceSets.creating {
-        dependsOn(sourceSets["commonMain"])
+        dependsOn(commonMainSourceSet)
     }
 
     targets.withType(KotlinNativeTarget::class.java).all {

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/native-platform-libraries/build.gradle.kts

@@ -10,8 +10,9 @@ repositories {
 }
 
 kotlin {
+    val commonMain by sourceSets.getting
     val nativeMain by sourceSets.creating {
-        dependsOn(sourceSets["commonMain"])
+        dependsOn(commonMain)
     }
 
     targets.withType(KotlinNativeTarget::class.java).all {

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/native-with-configuration-cache/build.gradle.kts

@@ -10,8 +10,9 @@ repositories {
 }
 
 kotlin {
+    val commonMainSourceSet = sourceSets.commonMain.get()
     val nativeMain by sourceSets.creating {
-        dependsOn(sourceSets["commonMain"])
+        dependsOn(commonMainSourceSet)
     }
 
     targets.withType(KotlinNativeTarget::class.java).all {

libraries/tools/kotlin-gradle-plugin/src/functionalTest/kotlin/org/jetbrains/kotlin/gradle/unitTests/KotlinMultiplatformSourceSetConventionsTest.kt

@@ -55,13 +55,9 @@ class KotlinMultiplatformSourceSetConventionsTest {
     fun `test - invoke - allows creating new source set in closure`() {
         val project = buildProjectWithMPP()
         project.multiplatformExtension.apply {
+            val fooSourceSet = sourceSets.create("foo")
             sourceSets.jvmMain {
-                /*
-                When done wrong, expect:
-                org.gradle.api.internal.AbstractMutationGuard$IllegalMutationException:
-                    NamedDomainObjectContainer#create(String) on KotlinSourceSet container cannot be executed in the current context
-                 */
-                dependsOn(sourceSets.create("foo"))
+                dependsOn(fooSourceSet)
             }
 
             assertEquals(setOf("foo"), sourceSets.jvmMain.get().dependsOn.map { it.name }.toSet())