[Gradle, JS] Default source-set name w/o legacy disambiguation in mixed

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/KotlinJsCompilation.kt

@@ -3,7 +3,9 @@
 * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
 */
 
-@file:Suppress("PackageDirectoryMismatch") // Old package for compatibility
+@file:Suppress("PackageDirectoryMismatch")
+
+// Old package for compatibility
 package org.jetbrains.kotlin.gradle.plugin.mpp
 
 import org.jetbrains.kotlin.gradle.dsl.KotlinJsOptions
@@ -11,6 +13,7 @@ import org.jetbrains.kotlin.gradle.plugin.KotlinCompilationWithResources
 import org.jetbrains.kotlin.gradle.plugin.KotlinTarget
 import org.jetbrains.kotlin.gradle.targets.js.npm.PackageJson
 import org.jetbrains.kotlin.gradle.tasks.Kotlin2JsCompile
+import org.jetbrains.kotlin.gradle.utils.lowerCamelCaseName
 
 open class KotlinJsCompilation(
     target: KotlinTarget,
@@ -28,4 +31,10 @@ import org.jetbrains.kotlin.gradle.tasks.Kotlin2JsCompile
     fun packageJson(handler: PackageJson.() -> Unit) {
         packageJsonHandlers.add(handler)
     }
+
+    override val defaultSourceSetName: String
+        get() = lowerCamelCaseName(
+            target.disambiguationClassifier?.removePrefix(LEGACY_DISAMBIGUATION_CLASSIFIER),
+            compilationName
+        )
 }

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/KotlinJsTargetConfigurator.kt

@@ -12,7 +12,6 @@ import org.jetbrains.kotlin.gradle.plugin.KotlinOnlyTargetConfigurator
 import org.jetbrains.kotlin.gradle.plugin.KotlinSourceSetProcessor
 import org.jetbrains.kotlin.gradle.plugin.KotlinTargetWithTestsConfigurator
 import org.jetbrains.kotlin.gradle.plugin.mpp.KotlinJsCompilation
-import org.jetbrains.kotlin.gradle.plugin.mpp.defaultSourceSetName
 import org.jetbrains.kotlin.gradle.targets.js.ir.KotlinJsIrTargetConfigurator
 import org.jetbrains.kotlin.gradle.tasks.KotlinTasksProvider
 import org.jetbrains.kotlin.gradle.testing.internal.kotlinTestRegistry

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/KotlinJsTargetPreset.kt

@@ -69,10 +69,12 @@ class KotlinJsSingleTargetPreset(
 
     // In a Kotlin/JS single-platform project, we don't need any disambiguation suffixes or prefixes in the names:
     override fun provideTargetDisambiguationClassifier(target: KotlinOnlyTarget<KotlinJsCompilation>): String? =
-        irPreset?.let { "legacy" }
+        irPreset?.let { LEGACY_DISAMBIGUATION_CLASSIFIER }
 
     override fun createKotlinTargetConfigurator() = KotlinJsTargetConfigurator(
         kotlinPluginVersion,
         irPreset?.let { KotlinJsIrTargetConfigurator(kotlinPluginVersion) }
     )
 }
+
+const val LEGACY_DISAMBIGUATION_CLASSIFIER = "legacy"