Report warning for several modules with same name on module path

compiler/cli/src/org/jetbrains/kotlin/cli/jvm/compiler/ClasspathRootsResolver.kt

@@ -154,8 +154,16 @@ internal class ClasspathRootsResolver(
         }
 
         for (module in modules) {
-            // TODO: report a diagnostic if a module with this name was already added
-            javaModuleFinder.addUserModule(module)
+            val existing = javaModuleFinder.findModule(module.name)
+            if (existing == null) {
+                javaModuleFinder.addUserModule(module)
+            }
+            else if (module.moduleRoot != existing.moduleRoot) {
+                val jar = VfsUtilCore.getVirtualFileForJar(module.moduleRoot) ?: module.moduleRoot
+                val existingPath = (VfsUtilCore.getVirtualFileForJar(existing.moduleRoot) ?: existing.moduleRoot).path
+                report(STRONG_WARNING, "The root is ignored because a module with the same name '${module.name}' " +
+                                       "has been found earlier on the module path at: $existingPath", jar)
+            }
         }
 
         if (javaModuleFinder.allObservableModules.none()) return

compiler/cli/src/org/jetbrains/kotlin/cli/jvm/modules/CliJavaModuleFinder.kt

@@ -26,13 +26,8 @@ import org.jetbrains.kotlin.resolve.jvm.modules.JavaModuleInfo
 internal class CliJavaModuleFinder(private val jrtFileSystem: VirtualFileSystem?) : JavaModuleFinder {
     private val userModules = linkedMapOf<String, JavaModule>()
 
-    /**
-     * @return true if the module was added successfully, false otherwise
-     */
-    fun addUserModule(module: JavaModule): Boolean {
-        if (module.name in userModules) return false
-        userModules[module.name] = module
-        return true
+    fun addUserModule(module: JavaModule) {
+        userModules.putIfAbsent(module.name, module)
     }
 
     val allObservableModules: Sequence<JavaModule>

compiler/testData/javaModules/severalModulesWithTheSameName/dependency1/foo/Foo.java

@@ -0,0 +1,3 @@
+package foo;
+
+public class Foo {}

compiler/testData/javaModules/severalModulesWithTheSameName/dependency1/module-info.java

@@ -0,0 +1,3 @@
+module dependency {
+    exports foo;
+}

compiler/testData/javaModules/severalModulesWithTheSameName/dependency2/bar/Bar.java

@@ -0,0 +1,3 @@
+package bar;
+
+public class Bar {}

compiler/testData/javaModules/severalModulesWithTheSameName/dependency2/module-info.java

@@ -0,0 +1,3 @@
+module dependency {
+    exports bar;
+}

compiler/testData/javaModules/severalModulesWithTheSameName/main.txt

@@ -0,0 +1,11 @@
+compiler/testData/javaModules/severalModulesWithTheSameName/main/usage.kt:2:8: error: unresolved reference: bar
+import bar.Bar
+       ^
+compiler/testData/javaModules/severalModulesWithTheSameName/main/usage.kt:6:12: error: unresolved reference: Bar
+    val b: Bar = Bar()
+           ^
+compiler/testData/javaModules/severalModulesWithTheSameName/main/usage.kt:6:18: error: unresolved reference: Bar
+    val b: Bar = Bar()
+                 ^
+$TMP_DIR$/dependency2.jar: warning: the root is ignored because a module with the same name 'dependency' has been found earlier on the module path at: $TMP_DIR$/dependency1.jar
+COMPILATION_ERROR

compiler/testData/javaModules/severalModulesWithTheSameName/main/module-info.java

@@ -0,0 +1,3 @@
+module main {
+    requires dependency;
+}

compiler/testData/javaModules/severalModulesWithTheSameName/main/usage.kt

@@ -0,0 +1,8 @@
+import foo.Foo
+import bar.Bar
+
+fun usage(): String {
+    val f: Foo = Foo()
+    val b: Bar = Bar()
+    return "$f$b"
+}

compiler/tests/org/jetbrains/kotlin/jvm/compiler/Java9ModulesIntegrationTest.kt

@@ -213,4 +213,10 @@ class Java9ModulesIntegrationTest : AbstractKotlinCompilerIntegrationTest() {
         val b = module("autoB")
         module("main", listOf(a, b))
     }
+
+    fun testSeveralModulesWithTheSameName() {
+        val d1 = module("dependency1")
+        val d2 = module("dependency2")
+        module("main", listOf(d1, d2))
+    }
 }