Disallow nested classes within inner & local classes

#KT-1174 In Progress

compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/Errors.java

@@ -522,6 +522,7 @@ public interface Errors {
     DiagnosticFactory1<JetSimpleNameExpression, ClassifierDescriptor> NO_CLASS_OBJECT = DiagnosticFactory1.create(ERROR);
 
     DiagnosticFactory1<PsiElement, ClassDescriptor> INACCESSIBLE_OUTER_CLASS_EXPRESSION = DiagnosticFactory1.create(ERROR);
+    SimpleDiagnosticFactory<PsiElement> NESTED_CLASS_NOT_ALLOWED = SimpleDiagnosticFactory.create(ERROR);
 
     ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
 

compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/rendering/DefaultErrorMessages.java

@@ -230,6 +230,7 @@ public class DefaultErrorMessages {
         MAP.put(NO_GENERICS_IN_SUPERTYPE_SPECIFIER, "Generic arguments of the base type must be specified");
 
         MAP.put(INACCESSIBLE_OUTER_CLASS_EXPRESSION, "Expression is inaccessible from a nested class ''{0}'', use ''inner'' keyword to make the class inner", NAME);
+        MAP.put(NESTED_CLASS_NOT_ALLOWED, "Nested class is not allowed here, use ''inner'' keyword to make the class inner");
 
         MAP.put(HAS_NEXT_MISSING, "hasNext() cannot be called on iterator() of type ''{0}''", RENDER_TYPE);
         MAP.put(HAS_NEXT_FUNCTION_AMBIGUITY, "hasNext() is ambiguous for iterator() of type ''{0}''", RENDER_TYPE);

compiler/frontend/src/org/jetbrains/jet/lang/resolve/ModifiersChecker.java

@@ -21,10 +21,12 @@ import com.google.common.collect.Maps;
 import com.google.common.collect.Sets;
 import com.intellij.lang.ASTNode;
 import com.intellij.openapi.util.Pair;
+import com.intellij.psi.PsiElement;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 import org.jetbrains.jet.lang.descriptors.*;
 import org.jetbrains.jet.lang.diagnostics.Errors;
+import org.jetbrains.jet.lang.psi.JetClass;
 import org.jetbrains.jet.lang.psi.JetModifierList;
 import org.jetbrains.jet.lang.psi.JetModifierListOwner;
 import org.jetbrains.jet.lexer.JetKeywordToken;
@@ -103,6 +105,14 @@ public class ModifiersChecker {
                 checkIllegalInThisContextModifiers(modifierList, Collections.singletonList(INNER_KEYWORD));
             }
         }
+        else {
+            if (modifierListOwner instanceof JetClass && isIllegalNestedClass(descriptor)) {
+                PsiElement name = ((JetClass) modifierListOwner).getNameIdentifier();
+                if (name != null) {
+                    trace.report(Errors.NESTED_CLASS_NOT_ALLOWED.on(name));
+                }
+            }
+        }
     }
 
     private static boolean isIllegalInner(@NotNull DeclarationDescriptor descriptor) {
@@ -114,6 +124,14 @@ public class ModifiersChecker {
         return ((ClassDescriptor) containingDeclaration).getKind() == ClassKind.TRAIT;
     }
 
+    private static boolean isIllegalNestedClass(@NotNull DeclarationDescriptor descriptor) {
+        if (!(descriptor instanceof ClassDescriptor)) return false;
+        DeclarationDescriptor containingDeclaration = descriptor.getContainingDeclaration();
+        if (!(containingDeclaration instanceof ClassDescriptor)) return false;
+        ClassDescriptor containingClass = (ClassDescriptor) containingDeclaration;
+        return containingClass.isInner() || containingClass.getContainingDeclaration() instanceof FunctionDescriptor;
+    }
+
     private void checkCompatibility(@Nullable JetModifierList modifierList, Collection<JetKeywordToken> availableModifiers, Collection<JetToken>... availableCombinations) {
         if (modifierList == null) return;
         Collection<JetKeywordToken> presentModifiers = Sets.newLinkedHashSet();

compiler/testData/codegen/dataClasses/copy/copyInNestedDataClass.kt

@@ -1,8 +1,8 @@
 class Bar(val name: String)
 
 class Baz {
-  class Foo() {
-      data class NestedFoo(val bar: Bar)
+  inner class Foo() {
+      inner data class NestedFoo(val bar: Bar)
 
       fun foo(): String {
           return NestedFoo(Bar("FAIL")).copy(bar = Bar("OK")).bar.name

compiler/testData/codegen/dataClasses/copy/copyInObjectNestedDataClass.kt

@@ -6,7 +6,7 @@ abstract class Foo {
 
 fun box(): String {
     return object: Foo() {
-      data class NestedFoo(val bar: Bar)
+      inner data class NestedFoo(val bar: Bar)
 
       override fun foo(): String {
         return NestedFoo(Bar("Fail")).copy(bar = Bar("OK")).bar.name

compiler/testData/codegen/regressions/kt2607.kt

@@ -1,7 +1,7 @@
 fun box() : String {
     val o = object {
 
-        class C {
+        inner class C {
             fun foo() = "OK"
         }
     }

compiler/testData/diagnostics/tests/inner/nestedClassNotAllowed.kt

@@ -0,0 +1,25 @@
+class A {
+    inner class B {
+        class <!NESTED_CLASS_NOT_ALLOWED!>C<!>
+    }
+    
+    fun foo() {
+        class B {
+            class <!NESTED_CLASS_NOT_ALLOWED!>C<!>
+        }
+    }
+}
+
+fun foo() {
+    class B {
+        class <!NESTED_CLASS_NOT_ALLOWED!>C<!>
+    }
+}
+
+
+enum class E {
+    E1 {
+        // Not allowed in Java, but no reason to disallow in Kotlin
+        class D
+    }
+}

compiler/tests/org/jetbrains/jet/checkers/JetDiagnosticsTestGenerated.java

@@ -2459,6 +2459,11 @@ public class JetDiagnosticsTestGenerated extends AbstractDiagnosticsTestWithEage
                 doTest("compiler/testData/diagnostics/tests/inner/nestedClassExtendsOuterGeneric.kt");
             }
             
+            @TestMetadata("nestedClassNotAllowed.kt")
+            public void testNestedClassNotAllowed() throws Exception {
+                doTest("compiler/testData/diagnostics/tests/inner/nestedClassNotAllowed.kt");
+            }
+            
             @TestMetadata("nestedVsInnerAccessOuterMember.kt")
             public void testNestedVsInnerAccessOuterMember() throws Exception {
                 doTest("compiler/testData/diagnostics/tests/inner/nestedVsInnerAccessOuterMember.kt");