Fix Java module descriptor configuration

build.gradle.kts

@@ -57,6 +57,7 @@ plugins {
     id("com.asarkar.gradle.build-time-tracker") version "3.0.1"
     id("org.jetbrains.dokka") version "1.6.21"
     id("ru.vyarus.use-python") version "2.3.0"
+    id("org.moditect.gradleplugin") version "1.0.0-rc3"
     id("com.github.johnrengelman.shadow") version "7.1.2"
     id("io.github.gradle-nexus.publish-plugin") version "1.1.0"
     `maven-publish`
@@ -98,6 +99,27 @@ tasks.test {
     maxParallelForks = 1
 }
 
+// Suppress warnings about incubating test suites feature
+@Suppress("UnstableApiUsage")
+testing {
+    suites {
+        // Separate test suite for module testing
+        val testModular by registering(JvmTestSuite::class) {
+            dependencies {
+                implementation(project)
+            }
+        }
+    }
+}
+
+// Module tests require Java 9 or newer to compile and execute
+if (JavaVersion.current().isJava9Compatible) {
+    tasks.check {
+        @Suppress("UnstableApiUsage")
+        dependsOn(testing.suites.named("testModular"))
+    }
+}
+
 tasks.jacocoTestReport {
     dependsOn("test")
     reports {
@@ -250,6 +272,22 @@ tasks.register<PythonTask>("writeAccuracyTable") {
     command = "src/python-scripts/write_accuracy_table.py"
 }
 
+tasks.addMainModuleInfo {
+    version = project.version
+    // Create Multi-Release JAR with Java 9 as lowest version
+    jvmVersion.set("9")
+    // Overwrite the output JAR file (if any) from a previous Gradle execution
+    overwriteExistingFiles.set(true)
+    module {
+        moduleInfoFile = File("$projectDir/src/main/java-9/module-info.java")
+    }
+}
+// Workaround to avoid circular dependencies between tasks, see https://github.com/moditect/moditect-gradle-plugin/issues/14
+project.afterEvaluate {
+    val compileJavaTask = tasks.compileJava.get()
+    compileJavaTask.setDependsOn(compileJavaTask.dependsOn - tasks.addDependenciesModuleInfo.get())
+}
+
 tasks.withType<DokkaTask>().configureEach {
     dokkaSourceSets.configureEach {
         jdkVersion.set(6)

src/main/java-9/module-info.java

@@ -0,0 +1,15 @@
+module com.github.pemistahl.lingua {
+    exports com.github.pemistahl.lingua.api;
+
+    requires kotlin.stdlib;
+
+    requires it.unimi.dsi.fastutil;
+    requires okio;
+
+    // Moshi accesses JSON serializer using reflection; must open the package
+    // TODO: Once new Moshi version has module names, change it to `opens ... to com.squareup.moshi`
+    //       and comment in the `requires` declarations below
+    opens com.github.pemistahl.lingua.internal;
+    // requires com.squareup.moshi;
+    // requires com.squareup.moshi.kotlin;
+}

src/testModular/java/module-info.java

@@ -0,0 +1,6 @@
+// Open complete module for reflection to allow JUnit to access the packages
+open module test {
+    requires com.github.pemistahl.lingua;
+
+    requires org.junit.jupiter.api;
+}

src/testModular/java/test/LinguaTest.java

@@ -0,0 +1,21 @@
+package test;
+
+import com.github.pemistahl.lingua.api.*;
+import org.junit.jupiter.api.Test;
+
+import static com.github.pemistahl.lingua.api.Language.*;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+/**
+ * Tests basic Lingua functionality. The main purpose of this test is to verify that the
+ * packages can be accessed from a different module and that Lingua specifies all required
+ * modules and can be used successfully.
+ */
+class LinguaTest {
+    @Test
+    void test() {
+        LanguageDetector detector = LanguageDetectorBuilder.fromLanguages(ENGLISH, FRENCH, GERMAN, SPANISH).build();
+        Language detectedLanguage = detector.detectLanguageOf("languages are awesome");
+        assertEquals(ENGLISH, detectedLanguage);
+    }
+}