Add pluginClasspaths to the configuration

build.gradle

@@ -41,6 +41,8 @@ idea {
 }
 
 dependencies {
+    testRuntime "org.jetbrains.kotlin:kotlin-scripting-compiler:1.3.50"
+
     implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8"
     testImplementation group: 'junit', name: 'junit', version: '4.12'
 
@@ -67,4 +69,4 @@ compileKotlin {
 compileTestKotlin {
     kotlinOptions.jvmTarget = "1.8"
     kotlinOptions.freeCompilerArgs += ["-Xskip-runtime-version-check"]
-}
+}

src/main/kotlin/com/tschuchort/compiletesting/KotlinCompilation.kt

@@ -65,6 +65,11 @@ class KotlinCompilation {
 	 */
 	var classpaths: List<File> = emptyList()
 
+	/**
+	 * Paths to plugins to be made available in the compilation
+	 */
+	var pluginClasspaths: List<File> = emptyList()
+
 	/** Source files to be compiled */
 	var sources: List<SourceFile> = emptyList()
 
@@ -326,6 +331,8 @@ class KotlinCompilation {
 		it.destination = classesDir.absolutePath
 		it.classpath = commonClasspaths().joinToString(separator = File.pathSeparator)
 
+		it.pluginClasspaths = pluginClasspaths.map(File::getAbsolutePath).toTypedArray()
+
 		if(jdkHome != null) {
 			it.jdkHome = jdkHome!!.absolutePath
 		}
@@ -403,6 +410,13 @@ class KotlinCompilation {
 
 	/** Performs the 1st and 2nd compilation step to generate stubs and run annotation processors */
 	private fun stubsAndApt(sourceFiles: List<File>): ExitCode {
+		pluginClasspaths.forEach { filepath ->
+			if (!filepath.exists()) {
+				error("Plugin $filepath not found")
+				return ExitCode.INTERNAL_ERROR
+			}
+		}
+
 		if(annotationProcessors.isEmpty()) {
 			log("No services were given. Not running kapt steps.")
 			return ExitCode.OK
@@ -473,10 +487,12 @@ class KotlinCompilation {
 			}
 		}
 
+		if (pluginClasspaths.isNotEmpty())
+			warn("Included plugins in pluginsClasspaths will be executed twice.")
+
 		val k2JvmArgs = commonK2JVMArgs().also {
 			it.freeArgs = sourcePaths
-			it.pluginClasspaths = (it.pluginClasspaths?.toList() ?: emptyList<String>() + getResourcesPath())
-					.distinct().toTypedArray()
+			it.pluginClasspaths = (it.pluginClasspaths ?: emptyArray()) + arrayOf(getResourcesPath())
 		}
 
 		val compilerMessageCollector = PrintingMessageCollector(

src/test/kotlin/com/tschuchort/compiletesting/KotlinCompilationTests.kt

@@ -1,11 +1,13 @@
 package com.tschuchort.compiletesting
 
 import com.tschuchort.compiletesting.KotlinCompilation.ExitCode
+import io.github.classgraph.ClassGraph
 import org.assertj.core.api.Assertions.assertThat
 import org.assertj.core.api.Assertions.fail
 import org.junit.Rule
 import org.junit.Test
 import org.junit.rules.TemporaryFolder
+import java.io.File
 import javax.annotation.processing.AbstractProcessor
 import javax.annotation.processing.RoundEnvironment
 import javax.lang.model.element.TypeElement
@@ -623,6 +625,28 @@ class KotlinCompilationTests {
 		assertClassLoadable(result, "${KotlinTestProcessor.GENERATED_PACKAGE}.${KotlinTestProcessor.GENERATED_JAVA_CLASS_NAME}")
 	}
 
+	@Test
+	fun `detects the plugin provided for compilation via pluginClasspaths property`() {
+		val result = defaultCompilerConfig().apply {
+			sources = listOf(SourceFile.kotlin("kSource.kt", "class KSource"))
+			pluginClasspaths = listOf(classpathOf("kotlin-scripting-compiler-1.3.50"))
+		}.compile()
+
+		assertThat(result.exitCode).isEqualTo(ExitCode.OK)
+		assertThat(result.messages).contains("provided plugin org.jetbrains.kotlin.scripting.compiler.plugin.ScriptingCompilerConfigurationComponentRegistrar")
+	}
+
+	@Test
+	fun `returns an internal error when adding a non existing plugin for compilation`() {
+		val result = defaultCompilerConfig().apply {
+			sources = listOf(SourceFile.kotlin("kSource.kt", "class KSource"))
+			pluginClasspaths = listOf(File("./non-existing-plugin.jar"))
+		}.compile()
+
+		assertThat(result.exitCode).isEqualTo(ExitCode.INTERNAL_ERROR)
+		assertThat(result.messages).contains("non-existing-plugin.jar not found")
+	}
+
 	private fun defaultCompilerConfig(): KotlinCompilation {
 		return KotlinCompilation().apply {
 			workingDir = temporaryFolder.root
@@ -645,6 +669,16 @@ class KotlinCompilationTests {
 			return fail<Nothing>("Class $className could not be loaded")
 		}
 	}
+
+	/**
+	 * Returns the classpath for a dependency (format $name-$version).
+	 * This is necessary to know the actual location of a dependency
+	 * which has been included in test runtime (build.gradle).
+	 */
+	private fun classpathOf(dependency: String): File {
+		val regex = Regex(".*$dependency\\.jar")
+		return ClassGraph().classpathFiles.first { classpath -> classpath.name.matches(regex) }
+	}
 
 	class InheritedClass {}
 }