Merge pull request #156 from crazyproger/KT-614

KT-614 Emit a warning when non-null type is checked for instance of nullable type

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

@@ -460,6 +460,8 @@ public interface Errors {
 
     DiagnosticFactory2<JetExpression, JetType, String> AUTOCAST_IMPOSSIBLE = DiagnosticFactory2.create(ERROR);
 
+    SimpleDiagnosticFactory<JetNullableType> USELESS_NULLABLE_CHECK = SimpleDiagnosticFactory.create(WARNING, NULLABLE_TYPE);
+
     // Properties / locals
 
     DiagnosticFactory1<JetExpression, DeclarationDescriptor> INITIALIZATION_USING_BACKING_FIELD_CUSTOM_SETTER = DiagnosticFactory1.create(ERROR);

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

@@ -223,6 +223,7 @@ public class DefaultErrorMessages {
         MAP.put(USELESS_CAST_STATIC_ASSERT_IS_FINE, "No cast needed, use ':' instead");
         MAP.put(USELESS_CAST, "No cast needed");
         MAP.put(CAST_NEVER_SUCCEEDS, "This cast can never succeed");
+        MAP.put(USELESS_NULLABLE_CHECK, "Non-null type is checked for instance of nullable type");
         MAP.put(WRONG_SETTER_PARAMETER_TYPE, "Setter parameter type must be equal to the type of the property, i.e. ''{0}''", RENDER_TYPE, RENDER_TYPE);
         MAP.put(WRONG_GETTER_RETURN_TYPE, "Getter return type must be equal to the type of the property, i.e. ''{0}''", RENDER_TYPE, RENDER_TYPE);
         MAP.put(NO_CLASS_OBJECT, "Please specify constructor invocation; classifier ''{0}'' does not have a class object", NAME);

compiler/frontend/src/org/jetbrains/jet/lang/types/expressions/PatternMatchingTypingVisitor.java

@@ -274,6 +274,12 @@ public class PatternMatchingTypingVisitor extends ExpressionTypingVisitor {
             return noChange(context);
         }
         JetType type = context.expressionTypingServices.getTypeResolver().resolveType(context.scope, typeReferenceAfterIs, context.trace, true);
+        if (!subjectType.isNullable() && type.isNullable()) {
+            JetTypeElement element = typeReferenceAfterIs.getTypeElement();
+            assert element instanceof JetNullableType : "element must be instance of " + JetNullableType.class.getName();
+            JetNullableType nullableType = (JetNullableType) element;
+            context.trace.report(Errors.USELESS_NULLABLE_CHECK.on(nullableType));
+        }
         checkTypeCompatibility(context, type, subjectType, typeReferenceAfterIs);
         if (BasicExpressionTypingVisitor.isCastErased(subjectType, type, JetTypeChecker.INSTANCE)) {
             context.trace.report(Errors.CANNOT_CHECK_FOR_ERASED.on(typeReferenceAfterIs, type));

compiler/testData/diagnostics/tests/cast/kt614.kt

@@ -0,0 +1 @@
+fun f(a: Collection<*>) = a is List<*><!USELESS_NULLABLE_CHECK!>?<!>

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

@@ -783,6 +783,11 @@ public class JetDiagnosticsTestGenerated extends AbstractDiagnosticsTestWithEage
                 doTest("compiler/testData/diagnostics/tests/cast/IsTraits.kt");
             }
             
+            @TestMetadata("kt614.kt")
+            public void testKt614() throws Exception {
+                doTest("compiler/testData/diagnostics/tests/cast/kt614.kt");
+            }
+            
             @TestMetadata("WhenErasedDisallowFromAny.kt")
             public void testWhenErasedDisallowFromAny() throws Exception {
                 doTest("compiler/testData/diagnostics/tests/cast/WhenErasedDisallowFromAny.kt");