Checks for . and ?.

idea/src/org/jetbrains/jet/lang/ErrorHandler.java

@@ -18,7 +18,7 @@ public class ErrorHandler {
         }
 
         @Override
-        public void structuralError(ASTNode node, String errorMessage) {
+        public void genericError(ASTNode node, String errorMessage) {
             throw new IllegalStateException(errorMessage);
         }
 
@@ -36,12 +36,15 @@ public class ErrorHandler {
     public void unresolvedReference(JetReferenceExpression referenceExpression) {
     }
 
-    public void structuralError(ASTNode node, String errorMessage) {
-    }
-
     public void typeMismatch(JetExpression expression, JetType expectedType, JetType actualType) {
     }
 
     public void redeclaration(DeclarationDescriptor existingDescriptor, DeclarationDescriptor redeclaredDescriptor) {
     }
+
+    public void genericError(ASTNode node, String errorMessage) {
+    }
+
+    public void genericWarning(ASTNode node, String message) {
+    }
 }

idea/src/org/jetbrains/jet/lang/annotations/JetPsiChecker.java

@@ -50,11 +50,6 @@ public class JetPsiChecker implements Annotator {
                         }
                     }
 
-                    @Override
-                    public void structuralError(ASTNode node, String errorMessage) {
-                        holder.createErrorAnnotation(node, errorMessage);
-                    }
-
                     @Override
                     public void typeMismatch(JetExpression expression, JetType expectedType, JetType actualType) {
                         holder.createErrorAnnotation(expression, "Type mismatch: inferred type is " + actualType + " but " + expectedType + " was expected");
@@ -65,6 +60,16 @@ public class JetPsiChecker implements Annotator {
                         redeclarations.add(existingDescriptor);
                         redeclarations.add(redeclaredDescriptor);
                     }
+
+                    @Override
+                    public void genericError(ASTNode node, String errorMessage) {
+                        holder.createErrorAnnotation(node, errorMessage);
+                    }
+
+                    @Override
+                    public void genericWarning(ASTNode node, String message) {
+                        holder.createWarningAnnotation(node, message);
+                    }
                 });
                 for (DeclarationDescriptor redeclaration : redeclarations) {
                     PsiElement declarationPsiElement = bindingContext.getDeclarationPsiElement(redeclaration);

idea/src/org/jetbrains/jet/lang/resolve/ClassDescriptorResolver.java

@@ -159,7 +159,7 @@ public class ClassDescriptorResolver {
             }
         } else {
             if (bodyExpression == null) {
-                semanticServices.getErrorHandler().structuralError(function.getNode(), "This function must either declare a return type or have a body expression");
+                semanticServices.getErrorHandler().genericError(function.getNode(), "This function must either declare a return type or have a body expression");
                 returnType = ErrorType.createErrorType("No type, no body");
             } else {
                 // TODO : Recursion possible
@@ -184,7 +184,7 @@ public class ClassDescriptorResolver {
 
             JetType type;
             if (typeReference == null) {
-                semanticServices.getErrorHandler().structuralError(valueParameter.getNode(), "A type annotation is required on a value parameter " + valueParameter.getName());
+                semanticServices.getErrorHandler().genericError(valueParameter.getNode(), "A type annotation is required on a value parameter " + valueParameter.getName());
                 type = ErrorType.createErrorType("Type annotation was missing");
             } else {
                 type = typeResolver.resolveType(parameterScope, typeReference);
@@ -265,7 +265,7 @@ public class ClassDescriptorResolver {
         if (propertyTypeRef == null) {
             JetExpression initializer = property.getInitializer();
             if (initializer == null) {
-                semanticServices.getErrorHandler().structuralError(property.getNode(), "This property must either have a type annotation or be initialized");
+                semanticServices.getErrorHandler().genericError(property.getNode(), "This property must either have a type annotation or be initialized");
                 type = ErrorType.createErrorType("No type, no body");
             } else {
                 // TODO : ??? Fix-point here: what if we have something like "val a = foo {a.bar()}"

idea/src/org/jetbrains/jet/lang/types/JetTypeInferrer.java

@@ -137,11 +137,13 @@ public class JetTypeInferrer {
             @Override
             public void visitQualifiedExpression(JetQualifiedExpression expression) {
                 // . or ?.
+                JetType receiverType = getType(scope, expression.getReceiverExpression(), false);
+                checkNullSafety(receiverType, expression);
+
                 JetExpression selectorExpression = expression.getSelectorExpression();
                 if (selectorExpression instanceof JetSimpleNameExpression) {
                     JetSimpleNameExpression referenceExpression = (JetSimpleNameExpression) selectorExpression;
 
-                    JetType receiverType = getType(scope, expression.getReceiverExpression(), false);
                     if (receiverType != null) {
                         result[0] = semanticServices.getOverloadResolver().getOverloadDomain(receiverType, scope, referenceExpression.getReferencedName());
                         reference[0] = referenceExpression;
@@ -172,6 +174,17 @@ public class JetTypeInferrer {
         return wrapForTracing(result[0], reference[0], true);
     }
 
+    private void checkNullSafety(JetType receiverType, JetQualifiedExpression expression) {
+        if (receiverType != null) {
+            if (receiverType.isNullable() && expression.getOperationSign() == JetTokens.DOT) {
+                semanticServices.getErrorHandler().genericError(expression.getOperationTokenNode(), "Only safe calls (?.) are allowed on a nullable receiver of type " + receiverType);
+            }
+            else if (!receiverType.isNullable() && expression.getOperationSign() == JetTokens.SAFE_ACCESS) {
+                semanticServices.getErrorHandler().genericWarning(expression.getOperationTokenNode(), "Unnecessary safe call on a non-null receiver of type  " + receiverType);
+            }
+        }
+    }
+
     private OverloadDomain wrapForTracing(final OverloadDomain overloadDomain, @NotNull final JetReferenceExpression referenceExpression, final boolean reportUnresolved) {
         if (overloadDomain == null) return OverloadDomain.EMPTY;
         return new OverloadDomain() {
@@ -408,7 +421,7 @@ public class JetTypeInferrer {
                     // TODO : Check for cast impossibility
                 }
                 else {
-                    semanticServices.getErrorHandler().structuralError(expression.getOperationSign().getNode(), "Unsupported binary operation");
+                    semanticServices.getErrorHandler().genericError(expression.getOperationSign().getNode(), "Unsupported binary operation");
                 }
                 result = targetType;
             }
@@ -422,7 +435,7 @@ public class JetTypeInferrer {
                 JetType conditionType = getType(scope, condition, false);
 
                 if (conditionType != null && !isBoolean(conditionType)) {
-                    semanticServices.getErrorHandler().structuralError(condition.getNode(), "Condition must be of type Boolean, but was of type " + conditionType);
+                    semanticServices.getErrorHandler().genericError(condition.getNode(), "Condition must be of type Boolean, but was of type " + conditionType);
                 }
             }
             // TODO : change types according to is and nullability checks
@@ -517,14 +530,29 @@ public class JetTypeInferrer {
         }
 
         @Override
-        public void visitDotQualifiedExpression(JetDotQualifiedExpression expression) {
+        public void visitHashQualifiedExpression(JetHashQualifiedExpression expression) {
+            throw new UnsupportedOperationException(); // TODO
+        }
+
+        @Override
+        public void visitPredicateExpression(JetPredicateExpression expression) {
+            throw new UnsupportedOperationException(); // TODO
+        }
+
+        @Override
+        public void visitQualifiedExpression(JetQualifiedExpression expression) {
             // TODO : functions
             JetExpression receiverExpression = expression.getReceiverExpression();
             JetExpression selectorExpression = expression.getSelectorExpression();
             JetType receiverType = getType(scope, receiverExpression, false);
-            if (receiverType != null && selectorExpression != null) { // TODO : review
-                JetScope compositeScope = new ScopeWithReceiver(scope, receiverType);
-                result = getType(compositeScope, selectorExpression, false);
+            if (receiverType != null) {
+                checkNullSafety(receiverType, expression);
+                if (selectorExpression != null) {
+                    // TODO : review
+
+                    JetScope compositeScope = new ScopeWithReceiver(scope, receiverType);
+                    result = getType(compositeScope, selectorExpression, false);
+                }
             }
         }
 
@@ -597,7 +625,7 @@ public class JetTypeInferrer {
             JetSimpleNameExpression operationSign = expression.getOperationSign();
             String name = unaryOperationNames.get(operationSign.getReferencedNameElementType());
             if (name == null) {
-                semanticServices.getErrorHandler().structuralError(operationSign.getNode(), "Unknown unary operation");
+                semanticServices.getErrorHandler().genericError(operationSign.getNode(), "Unknown unary operation");
             }
             else {
                 JetType type = getType(scope, expression.getBaseExpression(), false);
@@ -645,7 +673,7 @@ public class JetTypeInferrer {
                     if (constructor.equals(intTypeConstructor)) {
                         result = standardLibrary.getBooleanType();
                     } else {
-                        semanticServices.getErrorHandler().structuralError(operationSign.getNode(), "compareTo must return Int, but returns " + compareToReturnType);
+                        semanticServices.getErrorHandler().genericError(operationSign.getNode(), "compareTo must return Int, but returns " + compareToReturnType);
                     }
                 }
             }
@@ -692,7 +720,7 @@ public class JetTypeInferrer {
                 result = semanticServices.getStandardLibrary().getBooleanType();
             }
             else {
-                semanticServices.getErrorHandler().structuralError(operationSign.getNode(), "Unknown operation");
+                semanticServices.getErrorHandler().genericError(operationSign.getNode(), "Unknown operation");
             }
         }
 
@@ -700,7 +728,7 @@ public class JetTypeInferrer {
             if (resultType != null) {
                 // TODO : Relax?
                 if (!isBoolean(resultType)) {
-                    semanticServices.getErrorHandler().structuralError(operationSign.getNode(), "'" + name + "' must return Boolean but returns " + resultType);
+                    semanticServices.getErrorHandler().genericError(operationSign.getNode(), "'" + name + "' must return Boolean but returns " + resultType);
                     return null;
                 } else {
                     return resultType;