Add warning for initializers with obsolete syntax

Expected 'init' keyword before class initializer

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java

@@ -159,6 +159,7 @@ public interface Errors {
     DiagnosticFactory0<JetSecondaryConstructor> SECONDARY_CONSTRUCTOR_IN_OBJECT = DiagnosticFactory0.create(ERROR);
     DiagnosticFactory0<JetDelegatorToSuperCall> SUPERTYPE_INITIALIZED_WITHOUT_PRIMARY_CONSTRUCTOR = DiagnosticFactory0.create(ERROR);
     DiagnosticFactory0<JetConstructorDelegationCall> PRIMARY_CONSTRUCTOR_DELEGATION_CALL_EXPECTED = DiagnosticFactory0.create(ERROR);
+    DiagnosticFactory0<PsiElement> INIT_KEYWORD_BEFORE_CLASS_INITIALIZER_EXPECTED = DiagnosticFactory0.create(WARNING);
 
     // Trait-specific
 

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/DefaultErrorMessages.java

@@ -418,6 +418,8 @@ public class DefaultErrorMessages {
         MAP.put(SUPERTYPE_INITIALIZED_WITHOUT_PRIMARY_CONSTRUCTOR, "Supertype initialization is impossible without primary constructor");
         MAP.put(PRIMARY_CONSTRUCTOR_DELEGATION_CALL_EXPECTED, "Primary constructor call expected");
 
+        MAP.put(INIT_KEYWORD_BEFORE_CLASS_INITIALIZER_EXPECTED, "Expecting 'init' keyword before class initializer");
+
         MAP.put(ILLEGAL_SELECTOR, "Expression ''{0}'' cannot be a selector (occur after a dot)", STRING);
 
         MAP.put(NO_TAIL_CALLS_FOUND, "A function is marked as tail-recursive but no tail calls are found");

compiler/frontend/src/org/jetbrains/kotlin/psi/JetClassInitializer.java

@@ -20,6 +20,7 @@ import com.intellij.lang.ASTNode;
 import com.intellij.psi.PsiElement;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
+import org.jetbrains.kotlin.lexer.JetTokens;
 import org.jetbrains.kotlin.psi.stubs.KotlinPlaceHolderStub;
 import org.jetbrains.kotlin.psi.stubs.elements.JetStubElementTypes;
 
@@ -49,4 +50,14 @@ public class JetClassInitializer extends JetDeclarationStub<KotlinPlaceHolderStu
         JetExpression body = getBody();
         return (body instanceof JetBlockExpression) ? ((JetBlockExpression) body).getLBrace() : null;
     }
+
+    @NotNull
+    public PsiElement getOpenBraceNodeOrSelf() {
+        PsiElement result = getOpenBraceNode();
+        return result != null ? result : this;
+    }
+
+    public boolean hasInitKeyword() {
+        return findChildByType(JetTokens.INIT_KEYWORD) != null;
+    }
 }

compiler/frontend/src/org/jetbrains/kotlin/resolve/BodyResolver.java

@@ -451,6 +451,10 @@ public class BodyResolver {
             @NotNull JetClassInitializer anonymousInitializer,
             @NotNull ClassDescriptorWithResolutionScopes classDescriptor
     ) {
+        if (!anonymousInitializer.hasInitKeyword()) {
+            trace.report(INIT_KEYWORD_BEFORE_CLASS_INITIALIZER_EXPECTED.on(anonymousInitializer.getOpenBraceNodeOrSelf()));
+        }
+
         JetScope scopeForInitializers = classDescriptor.getScopeForInitializerResolution();
         if (!classDescriptor.getConstructors().isEmpty()) {
             expressionTypingServices.getType(scopeForInitializers, anonymousInitializer.getBody(), NO_EXPECTED_TYPE, c.getOuterDataFlowInfo(), trace);