[Gradle] Implement KT54867KotlinWithJavaCompilationClasspathTest to cover KT-54867

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/dsl/KotlinProjectExtension.kt

@@ -53,6 +53,12 @@ internal val Project.kotlinExtensionOrNull: KotlinProjectExtension?
 val Project.kotlinExtension: KotlinProjectExtension
     get() = extensions.getByName(KOTLIN_PROJECT_EXTENSION_NAME).castIsolatedKotlinPluginClassLoaderAware()
 
+internal val Project.kotlinJvmExtensionOrNull: KotlinJvmProjectExtension?
+    get() = extensions.findByName(KOTLIN_PROJECT_EXTENSION_NAME)?.castIsolatedKotlinPluginClassLoaderAware()
+
+internal val Project.kotlinJvmExtension: KotlinJvmProjectExtension
+    get() = extensions.getByName(KOTLIN_PROJECT_EXTENSION_NAME).castIsolatedKotlinPluginClassLoaderAware()
+
 internal val Project.multiplatformExtensionOrNull: KotlinMultiplatformExtension?
     get() = extensions.findByName(KOTLIN_PROJECT_EXTENSION_NAME)?.castIsolatedKotlinPluginClassLoaderAware()
 

libraries/tools/kotlin-gradle-plugin/src/functionalTest/kotlin/org/jetbrains/kotlin/gradle/KT54867KotlinWithJavaCompilationClasspathTest.kt

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2010-2022 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * 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("FunctionName")
+
+package org.jetbrains.kotlin.gradle
+
+import org.jetbrains.kotlin.gradle.dsl.kotlinJvmExtension
+import org.jetbrains.kotlin.gradle.plugin.mpp.javaSourceSets
+import org.junit.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertSame
+
+class KT54867KotlinWithJavaCompilationClasspathTest {
+
+    @Test
+    fun `test - jvm project - kotlin with java compilation - setting classpath on javaSourceSet`() {
+        val project = buildProjectWithJvm {
+            enableDefaultStdlibDependency(false)
+        }
+
+        val customJavaSourceSet = project.javaSourceSets.create("custom")
+        val customKotlinSourceSet = project.kotlinJvmExtension.sourceSets.getByName("custom")
+        val customKotlinCompilation = project.kotlinJvmExtension.target.compilations.getByName("custom")
+
+        assertSame(customKotlinSourceSet, customKotlinCompilation.defaultSourceSet)
+        assertSame(customJavaSourceSet, customKotlinCompilation.javaSourceSet)
+
+        customJavaSourceSet.compileClasspath = project.files("compile", "classpath")
+        customJavaSourceSet.runtimeClasspath = project.files("runtime", "classpath")
+
+        assertEquals(
+            project.files("compile", "classpath").files, customKotlinCompilation.compileDependencyFiles.files
+        )
+
+        assertEquals(
+            project.files("runtime", "classpath").files, customKotlinCompilation.runtimeDependencyFiles.files
+        )
+    }
+}