Introduce Java 9 module compatibility

core/build.gradle

@@ -61,17 +61,23 @@ tasks.withType(Jar) {
 tasks.trimShadedJar.doLast {
     // outjars is a file, so only one jar generated for sure
     def trimmed = tasks.trimShadedJar.outJarFiles[0].toPath()
-    ant.jar(destfile: trimmed.toString(), update: true) {
+
+    ant.jar(destfile: trimmed.toString(), update: true, duplicate: 'fail') {
         zipfileset(src: tasks.shadedJar.archivePath) {
             include(name: 'META-INF/versions/**')
         }
+
+        // Do not let Ant put the properties that harm the build reproducibility, such as JDK version.
+        delegate.manifest {
+            attribute(name: 'Created-By', value: "Gradle ${gradle.gradleVersion}")
+        }
     }
 }
 
 tasks.shadedTest.exclude 'META-INF/versions/**'
 
 dependencies {
-    mrJarVersions.each { version->
+    mrJarVersions.each { version ->
         // Common to reference classes in main sourceset from Java 9 one (e.g., to return a common interface)
         "java${version}Implementation" files(sourceSets.main.output.classesDirs) { builtBy compileJava }
 

gradle.properties

@@ -19,6 +19,7 @@ publishUrlForSnapshot=https://oss.sonatype.org/content/repositories/snapshots/
 publishUsernameProperty=ossrhUsername
 publishPasswordProperty=ossrhPassword
 publishSignatureRequired=true
+automaticModuleNames=true
 
 # Gradle options
 org.gradle.jvmargs=-Xmx2048m -XX:+HeapDumpOnOutOfMemoryError

gradle/scripts/README.md

@@ -34,6 +34,7 @@ sensible defaults. By applying them, you can:
     - [Shading a multi-module project with `relocate` flag](#shading-a-multi-module-project-with-relocate-flag)
 - [Setting a Java target version with the `java(\\d+)` flag](#setting-a-java-target-version-with-the-javad-flag)
 - [Setting a Kotlin target version with the `kotlin(\\d+\\.\\d+)` flag](#setting-a-koltin-target-version-with-the-kotlindd-flag)
+- [Automatic module names](#automatic-module-names)
 - [Tagging conveniently with `release` task](#tagging-conveniently-with-release-task)
 
 <!-- /MarkdownTOC -->
@@ -98,6 +99,7 @@ sensible defaults. By applying them, you can:
    ```
    group=com.doe.john.myexample
    version=0.0.1-SNAPSHOT
+   versionPattern=^[0-9]+\\.[0-9]+\\.[0-9]+$
    projectName=My Example
    projectUrl=https://www.example.com/
    projectDescription=My example project
@@ -118,6 +120,7 @@ sensible defaults. By applying them, you can:
    googleAnalyticsId=UA-XXXXXXXX
    javaSourceCompatibility=1.8
    javaTargetCompatibility=1.8
+   automaticModuleNames=false
    ```
 
 5. That's all. You now have two Java subprojects with sensible defaults.
@@ -672,6 +675,31 @@ However, if you want to compile a Kotlin module with a different language versio
 
 For example, `kotlin1.6` flag makes your Kotlin module compatible with language version 1.6 and API version 1.6.
 
+## Automatic module names
+
+By specifying the `automaticModuleNames=true` property in `settings.gradle`, every `java` project's JAR
+file will contain the `Automatic-Module-Name` property in its `MANIFEST.MF`, auto-generated from the group ID
+and artifact ID. For example:
+
+- groupId: `com.example`, artifactId: `foo-bar`
+  - module name: `com.example.foo.bar`
+- groupId: `com.example.foo`, artifactId: `foo-bar`
+  - module name: `com.example.foo.bar`
+
+If enabled, each project with `java` flag will have the `automaticModuleName` property.
+
+You can override the automatic module name of a certain project via the `automaticModuleNameOverrides`
+extension property:
+
+    ```groovy
+    ext {
+        // Change the automatic module name of project ':bar' to 'com.example.fubar'.
+        automaticModuleNameOverrides = [
+            ':bar': 'com.example.fubar'
+        ]
+    }
+    ```
+
 ## Tagging conveniently with `release` task
 
 The task called `release` is added at the top level project. It will update the

gradle/scripts/lib/common-info.gradle

@@ -42,17 +42,9 @@ allprojects {
     ext {
         artifactId = {
             // Use the overridden one if available.
-            if (rootProject.ext.has('artifactIdOverrides')) {
-                def overrides = rootProject.ext.artifactIdOverrides
-                if (!(overrides instanceof Map)) {
-                    throw new IllegalStateException("artifactIdOverrides must be a Map: ${overrides}")
-                }
-
-                for (Map.Entry<String, String> e : overrides.entrySet()) {
-                    if (rootProject.project(e.key) == project) {
-                        return e.value
-                    }
-                }
+            def overriddenArtifactId = findOverridden('artifactIdOverrides', project)
+            if (overriddenArtifactId != null) {
+                return overriddenArtifactId
             }
 
             // Generate from the project names otherwise.
@@ -70,3 +62,49 @@ allprojects {
         }.call()
     }
 }
+
+// Check whether to enable automatic module names.
+def isAutomaticModuleNameEnabled = 'true' == rootProject.findProperty('automaticModuleNames')
+
+allprojects {
+    ext {
+        automaticModuleName = {
+            if (!isAutomaticModuleNameEnabled) {
+                return null
+            }
+
+            // Use the overridden one if available.
+            def overriddenAutomaticModuleName = findOverridden('automaticModuleNameOverrides', project)
+            if (overriddenAutomaticModuleName != null) {
+                return overriddenAutomaticModuleName
+            }
+
+            // Generate from the groupId and artifactId otherwise.
+            def groupIdComponents = String.valueOf(rootProject.group).split("\\.").toList()
+            def artifactIdComponents =
+                    String.valueOf(project.ext.artifactId).replace('-', '.').split("\\.").toList()
+            if (groupIdComponents.last() == artifactIdComponents.first()) {
+                return String.join('.', groupIdComponents + artifactIdComponents.drop(1))
+            } else {
+                return String.join('.', groupIdComponents + artifactIdComponents)
+            }
+        }.call()
+    }
+}
+
+def findOverridden(String overridesPropertyName, Project project) {
+    if (rootProject.ext.has(overridesPropertyName)) {
+        def overrides = rootProject.ext.get(overridesPropertyName)
+        if (!(overrides instanceof Map)) {
+            throw new IllegalStateException("rootProject.ext.${overridesPropertyName} must be a Map: ${overrides}")
+        }
+
+        for (Map.Entry<String, String> e : overrides.entrySet()) {
+            if (rootProject.project(e.key) == project) {
+                return String.valueOf(e.value)
+            }
+        }
+    }
+
+    return null
+}

gradle/scripts/lib/java-shade.gradle

@@ -27,12 +27,23 @@ configure(relocatedProjects) {
         configureShadowTask(project, delegate, true)
         archiveBaseName.set("${project.archivesBaseName}-shaded")
 
+        // Exclude the legacy file listing.
+        exclude '/META-INF/INDEX.LIST'
         // Exclude the class signature files.
         exclude '/META-INF/*.SF'
         exclude '/META-INF/*.DSA'
         exclude '/META-INF/*.RSA'
         // Exclude the files generated by Maven
         exclude '/META-INF/maven/**'
+        // Exclude the module metadata that'll become invalid after relocation.
+        exclude '**/module-info.class'
+
+        // Set the 'Automatic-Module-Name' property in MANIFEST.MF.
+        if (project.ext.automaticModuleName != null) {
+            manifest {
+                attributes('Automatic-Module-Name': project.ext.automaticModuleName)
+            }
+        }
     }
     tasks.assemble.dependsOn tasks.shadedJar
 

gradle/scripts/lib/java.gradle

@@ -1,5 +1,6 @@
 import java.util.regex.Pattern
 
+// Determine which version of JDK should be used for builds.
 def buildJdkVersion = Integer.parseInt(JavaVersion.current().getMajorVersion())
 if (rootProject.hasProperty('buildJdkVersion')) {
     def jdkVersion = Integer.parseInt(String.valueOf(rootProject.findProperty('buildJdkVersion')))
@@ -139,6 +140,12 @@ configure(projectsWithFlags('java')) {
         registerFeature('optional') {
             usingSourceSet(sourceSets.main)
         }
+
+        // Do not let Gradle infer the module path if automatic module name is enabled,
+        // because it means the JAR will rely on JDK's automatic module metadata generation.
+        if (project.ext.automaticModuleName != null) {
+            modularity.inferModulePath = false
+        }
     }
 
     // Set the sensible compiler options.
@@ -154,6 +161,15 @@ configure(projectsWithFlags('java')) {
         options.compilerArgs += '-parameters'
     }
 
+    // Set the 'Automatic-Module-Name' property in 'MANIFEST.MF' if `automaticModuleName` is not null.
+    if (project.ext.automaticModuleName != null) {
+        tasks.named('jar') {
+            manifest {
+                attributes('Automatic-Module-Name': project.ext.automaticModuleName)
+            }
+        }
+    }
+
     project.ext.configureFlakyTests = { Test testTask ->
         def flakyTests = rootProject.findProperty('flakyTests')
         if (flakyTests == 'true') {

gradle/scripts/lib/prerequisite.gradle

@@ -9,12 +9,15 @@ plugins {
 ''')
 }
 
-['projectName', 'projectUrl', 'inceptionYear', 'licenseName', 'licenseUrl', 'scmUrl', 'scmConnection',
+['group', 'version', 'projectName', 'projectUrl', 'inceptionYear', 'licenseName', 'licenseUrl', 'scmUrl', 'scmConnection',
  'scmDeveloperConnection', 'publishUrlForRelease', 'publishUrlForSnapshot', 'publishUsernameProperty',
  'publishPasswordProperty'].each {
     if (rootProject.findProperty(it) == null) {
         throw new IllegalStateException('''Add project info properties to gradle.properties:
 
+group=com.doe.john.myexample
+version=0.0.1-SNAPSHOT
+versionPattern=^[0-9]+\\\\.[0-9]+\\\\.[0-9]+$
 projectName=My Example
 projectUrl=https://www.example.com/
 projectDescription=My example project
@@ -31,7 +34,12 @@ publishUrlForRelease=https://oss.sonatype.org/service/local/staging/deploy/maven
 publishUrlForSnapshot=https://oss.sonatype.org/content/repositories/snapshots/
 publishUsernameProperty=ossrhUsername
 publishPasswordProperty=ossrhPassword
+publishSignatureRequired=true
 versionPattern=^[0-9]+\\\\.[0-9]+\\\\.[0-9]+$
+googleAnalyticsId=UA-XXXXXXXX
+javaSourceCompatibility=1.8
+javaTargetCompatibility=1.8
+automaticModuleNames=false
 ''')
     }
 }