Improve modular JDK root module detection

According to the spec, "java.se" and every other non-"java.*" module
that exports at least one package without qualification, is a root.
Currently we only support compilation of a single unnamed module, and
apparently unnamed module should read all root modules.

 #KT-18180 Fixed

compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/modules/JavaModuleFinder.kt

@@ -0,0 +1,21 @@
+/*
+ * Copyright 2010-2017 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.jetbrains.kotlin.resolve.jvm.modules
+
+interface JavaModuleFinder {
+    fun findModule(name: String): JavaModuleInfo?
+}

compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/modules/JavaModuleGraph.kt

@@ -18,22 +18,25 @@ package org.jetbrains.kotlin.resolve.jvm.modules
 
 import org.jetbrains.kotlin.storage.LockBasedStorageManager
 
-class JavaModuleGraph(getModuleInfo: (String) -> JavaModuleInfo) {
-    private val moduleInfo: (String) -> JavaModuleInfo = LockBasedStorageManager.NO_LOCKS.createMemoizedFunction(getModuleInfo)
+class JavaModuleGraph(finder: JavaModuleFinder) {
+    private val moduleInfo: (String) -> JavaModuleInfo? =
+            LockBasedStorageManager.NO_LOCKS.createMemoizedFunctionWithNullableValues(finder::findModule)
 
-    fun getAllReachable(rootModules: List<String>): List<String> {
-        val visited = linkedSetOf<String>()
+    fun getAllDependencies(moduleNames: List<String>): List<String> {
+        // Every module implicitly depends on java.base
+        val visited = linkedSetOf("java.base")
 
         fun dfs(module: String) {
             if (!visited.add(module)) return
-            for (dependency in moduleInfo(module).requires) {
+            val moduleInfo = moduleInfo(module) ?: return
+            for (dependency in moduleInfo.requires) {
                 if (dependency.isTransitive) {
                     dfs(dependency.moduleName)
                 }
             }
         }
 
-        rootModules.forEach(::dfs)
+        moduleNames.forEach(::dfs)
         return visited.toList()
     }
 }