Add module descriptor while maintaining Eclipse IDE experience

* Fixes ben-manes#535
* Uses Gradle Eclipse plugin to define add-reads options which
  satisfy Eclipse and make the project buildable through it in
  Eclipse 2021-03

Only the core caffeine module was eligible for a full module
  descriptor considering the circumstances:
* A descriptor was not added to caffeine-guava because some of
  its tests rely on split packages in order to acccess Guava's
  package-private types. Ensuring a smooth experience in
  Eclipse IDE requires resolving these split packages.
* The other modules still have some dependencies on filename-based
  modules, so it would be unwise to add module descriptors for
  them.

caffeine/build.gradle

@@ -23,8 +23,21 @@ idea.module {
   scopes.PROVIDED.plus += [ configurations.javaPoetCompileClasspath ]
 }
 
-eclipse.classpath.file.whenMerged {
-  entries.findAll { it instanceof SourceFolder && it.output == 'bin/codeGen' }*.output = 'bin/main'
+eclipse.classpath {
+  containers 'org.eclipse.buildship.core.gradleclasspathcontainer'
+  file {
+    whenMerged {
+      entries.findAll { it instanceof SourceFolder && it.output == 'bin/codeGen' }*.output = 'bin/main'
+      entries.findAll { it instanceof org.gradle.plugins.ide.eclipse.model.AbstractClasspathEntry }.each {
+        it.entryAttributes['module'] = 'true'
+      }
+      def modules = [ 'java.compiler', 'java.logging', 'jdk.unsupported', 'com.google.common',
+        'com.google.googlejavaformat', 'guava.testlib', 'it.unimi.dsi.fastutil', 'org.apache.commons.lang3',
+        'org.cache2k.api', 'org.hamcrest', 'org.jctools.core', 'org.mockito', 'org.testng' ]
+      def main = entries.find { it instanceof SourceFolder && it.path == 'src/main/java' }
+      main.entryAttributes['add-reads'] = buildAddReads('com.github.benmanes.caffeine', modules)
+    }
+  }
 }
 
 plugins.withType(EclipsePlugin) {
@@ -66,6 +79,10 @@ dependencies {
   javaPoetImplementation libraries.googleJavaFormat
 }
 
+compileJava {
+  modularity.inferModulePath = true
+}
+
 compileCodeGenJava {
   gradle.taskGraph.whenReady {
     enabled = gradle.taskGraph.hasTask('uploadArchives')

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

@@ -0,0 +1,8 @@
+
+module com.github.benmanes.caffeine {
+    exports com.github.benmanes.caffeine.cache;
+    exports com.github.benmanes.caffeine.cache.stats;
+
+    requires static transitive org.checkerframework.checker.qual;
+    requires static transitive com.google.errorprone.annotations;
+}

gradle/dependencies.gradle

@@ -41,7 +41,7 @@ ext {
     elasticSearch: '7.12.0',
     expiringMap: '0.5.9',
     fastfilter: '1.0',
-    fastutil: '8.5.4',
+    fastutil: '8.5.2',
     flipTables: '1.1.0',
     googleJavaFormat: '1.10.0',
     guava: '30.1.1-jre',
@@ -165,10 +165,14 @@ ext {
     jcacheTck: "javax.cache:cache-tests:${testVersions.jcacheTck}",
     jcacheTckTests: "javax.cache:cache-tests:${testVersions.jcacheTck}:tests",
     jctools: "org.jctools:jctools-core:${testVersions.jctools}",
-    junit: "junit:junit:${testVersions.junit}",
+    junit: dependencies.create("junit:junit:${testVersions.junit}") {
+      exclude group: 'org.hamcrest'
+    },
     mockito: "org.mockito:mockito-core:${testVersions.mockito}",
     osgiCompile: [
-      "org.ops4j.pax.exam:pax-exam-junit4:${testVersions.paxExam}",
+      dependencies.create("org.ops4j.pax.exam:pax-exam-junit4:${testVersions.paxExam}") {
+        exclude group: 'org.hamcrest'
+      },
     ],
     osgiRuntime: [
       "org.apache.felix:org.apache.felix.framework:${testVersions.felix}",

gradle/eclipse.gradle

@@ -48,3 +48,16 @@ def ignoreDerivedResources(projectDescription, directories = [
     }
   }
 }
+
+ext.buildAddReads = { subjectModule, addModules ->
+  def addReads = new StringBuilder()
+  addModules.each {
+    if (addReads.length() != 0) {
+      addReads.append(':')
+    }
+    addReads.append(subjectModule)
+    addReads.append('=')
+    addReads.append(it)
+  }
+  return addReads.toString()
+}