Allow to access unexported package of named module in unnamed module in IDE

#KT-19492 Fixed

idea/idea-analysis/src/org/jetbrains/kotlin/idea/modules/IdeJavaModuleResolver.kt

@@ -46,26 +46,23 @@ class IdeJavaModuleResolver(private val project: Project) : JavaModuleResolver {
             return JavaModuleResolver.AccessError.ModuleDoesNotReadModule(theirModule.name)
         }
 
-        val fqName = referencedPackage?.asString() ?: return null
+        // In the IDE, we allow unnamed module to access unexported package of the named module. The reason is that the compiler
-        if (!exports(theirModule, fqName, ourModule)) {
+        // will use classpath, not the module path, when compilation of this module is launched from the IDE (because the module has
-            return JavaModuleResolver.AccessError.ModuleDoesNotExportPackage(theirModule.name)
+        // no module-info). All of its dependencies will also land on the classpath, and everything is visible in the classpath,
+        // even non-exported packages of artifacts which would otherwise be loaded as named modules, if they were on the module path.
+        // So, no error will be reported from the compiler. Moreover, a run configuration of something from this unnamed module will also
+        // use classpath, not the module path, and in the same way everything will work at runtime as well.
+        if (ourModule != null) {
+            val fqName = referencedPackage?.asString() ?: return null
+            if (!exports(theirModule, fqName, ourModule)) {
+                return JavaModuleResolver.AccessError.ModuleDoesNotExportPackage(theirModule.name)
+            }
         }
 
         return null
     }
 
     // Returns whether or not [source] exports [packageName] to [target]
-    private fun exports(source: PsiJavaModule, packageName: String, target: PsiJavaModule?): Boolean {
+    private fun exports(source: PsiJavaModule, packageName: String, target: PsiJavaModule): Boolean =
-        if (source is LightJavaModule) {
+            source is LightJavaModule || JavaModuleGraphUtil.exports(source, packageName, target)
-            return true
-        }
-
-        // TODO: simply call JavaModuleGraphUtil.exports as soon as its 'target' parameter is nullable
-        if (target != null) {
-            return JavaModuleGraphUtil.exports(source, packageName, target)
-        }
-        return source.exports.any { statement ->
-            statement.moduleNames.isEmpty() && statement.packageName == packageName
-        }
-    }
 }

idea/testData/multiModuleHighlighting/java9/exportsTo/unnamed/unnamedUsage.kt

@@ -1,6 +1,6 @@
-import dependency.<error>Foo</error>
+import dependency.Foo
 
 fun unnamedUsage(): String {
-    val foo: <error>Foo</error> = <error>Foo</error>()
+    val foo: Foo = Foo()
-    return foo.<error>toString</error>()
+    return foo.toString()
 }

idea/testData/multiModuleHighlighting/java9/unnamedDependsOnNamed/main/usage.kt

@@ -2,15 +2,15 @@ import dependency.*
 import dependency.J
 import dependency.K
 import dependency.impl.*
-import dependency.impl.<error>JImpl</error>
+import dependency.impl.JImpl
-import dependency.impl.<error>KImpl</error>
+import dependency.impl.KImpl
 
 fun usage(): String {
     val j: J = J.getInstance()
     val k: K = K.getInstance()
 
-    val jImpl: <error>JImpl</error> = J.getInstance()
+    val jImpl: JImpl = J.getInstance()
-    val kImpl: <error>KImpl</error> = K.getInstance()
+    val kImpl: KImpl = K.getInstance()
 
     return "$j$k$jImpl$kImpl"
 }