Minor. Inline NO_RECEIVER_PARAMETER = null

compiler/backend/src/org/jetbrains/kotlin/codegen/AccessorForFunctionDescriptor.java

@@ -22,8 +22,6 @@ import org.jetbrains.kotlin.name.Name;
 import org.jetbrains.kotlin.resolve.DescriptorUtils;
 import org.jetbrains.kotlin.resolve.annotations.AnnotationsPackage;
 
-import static org.jetbrains.kotlin.descriptors.ReceiverParameterDescriptor.NO_RECEIVER_PARAMETER;
-
 public class AccessorForFunctionDescriptor extends AbstractAccessorForFunctionDescriptor implements AccessorForCallableDescriptor<FunctionDescriptor> {
 
     private final FunctionDescriptor calleeDescriptor;
@@ -39,7 +37,7 @@ public class AccessorForFunctionDescriptor extends AbstractAccessorForFunctionDe
 
         initialize(DescriptorUtils.getReceiverParameterType(descriptor.getExtensionReceiverParameter()),
                    descriptor instanceof ConstructorDescriptor || AnnotationsPackage.isPlatformStaticInObjectOrClass(descriptor)
-                        ? NO_RECEIVER_PARAMETER
+                        ? null
                         : descriptor.getDispatchReceiverParameter(),
                    copyTypeParameters(descriptor),
                    copyValueParameters(descriptor),

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

@@ -47,7 +47,6 @@ import org.jetbrains.kotlin.util.slicedMap.WritableSlice;
 
 import java.util.*;
 
-import static org.jetbrains.kotlin.descriptors.ReceiverParameterDescriptor.NO_RECEIVER_PARAMETER;
 import static org.jetbrains.kotlin.diagnostics.Errors.*;
 import static org.jetbrains.kotlin.resolve.BindingContext.*;
 import static org.jetbrains.kotlin.types.TypeUtils.NO_EXPECTED_TYPE;
@@ -669,7 +668,7 @@ public class BodyResolver {
         }
 
         JetScope propertyDeclarationInnerScope = JetScopeUtils.getPropertyDeclarationInnerScopeForInitializer(
-                propertyDescriptor, propertyScope, propertyDescriptor.getTypeParameters(), NO_RECEIVER_PARAMETER, trace);
+                propertyDescriptor, propertyScope, propertyDescriptor.getTypeParameters(), null, trace);
         JetScope accessorScope = JetScopeUtils.makeScopeForPropertyAccessor(
                 propertyDescriptor, parentScopeForAccessor, trace);
 
@@ -697,7 +696,7 @@ public class BodyResolver {
             @NotNull JetScope scope
     ) {
         JetScope propertyDeclarationInnerScope = JetScopeUtils.getPropertyDeclarationInnerScopeForInitializer(
-                propertyDescriptor, scope, propertyDescriptor.getTypeParameters(), NO_RECEIVER_PARAMETER, trace);
+                propertyDescriptor, scope, propertyDescriptor.getTypeParameters(), null, trace);
         JetType expectedTypeForInitializer = property.getTypeReference() != null ? propertyDescriptor.getType() : NO_EXPECTED_TYPE;
         if (propertyDescriptor.getCompileTimeInitializer() == null) {
             expressionTypingServices.getType(propertyDeclarationInnerScope, initializer, expectedTypeForInitializer,

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

@@ -50,7 +50,6 @@ import org.jetbrains.kotlin.types.expressions.ExpressionTypingServices;
 
 import java.util.*;
 
-import static org.jetbrains.kotlin.descriptors.ReceiverParameterDescriptor.NO_RECEIVER_PARAMETER;
 import static org.jetbrains.kotlin.diagnostics.Errors.*;
 import static org.jetbrains.kotlin.lexer.JetTokens.OVERRIDE_KEYWORD;
 import static org.jetbrains.kotlin.lexer.JetTokens.VARARG_KEYWORD;
@@ -735,7 +734,7 @@ public class DescriptorResolver {
         ReceiverParameterDescriptor receiverDescriptor =
                 DescriptorFactory.createExtensionReceiverParameterForCallable(propertyDescriptor, receiverType);
 
-        ReceiverParameterDescriptor implicitInitializerReceiver = property.hasDelegate() ? NO_RECEIVER_PARAMETER : receiverDescriptor;
+        ReceiverParameterDescriptor implicitInitializerReceiver = property.hasDelegate() ? null : receiverDescriptor;
 
         JetScope propertyScope = JetScopeUtils.getPropertyDeclarationInnerScope(propertyDescriptor, scope, typeParameterDescriptors,
                                                                                 implicitInitializerReceiver, trace);
@@ -1055,7 +1054,7 @@ public class DescriptorResolver {
                 toSourceElement(parameter)
         );
         propertyDescriptor.setType(type, Collections.<TypeParameterDescriptor>emptyList(),
-                                   getDispatchReceiverParameterIfNeeded(classDescriptor), NO_RECEIVER_PARAMETER);
+                                   getDispatchReceiverParameterIfNeeded(classDescriptor), (ReceiverParameterDescriptor) null);
 
         PropertyGetterDescriptorImpl getter = DescriptorFactory.createDefaultGetter(propertyDescriptor);
         PropertySetterDescriptor setter =

compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/descriptors/LazyScriptClassMemberScope.kt

@@ -103,7 +103,7 @@ public class LazyScriptClassMemberScope protected constructor(
                 returnType,
                 listOf<TypeParameterDescriptor>(),
                 scriptDescriptor.getThisAsReceiverParameter(),
-                ReceiverParameterDescriptor.NO_RECEIVER_PARAMETER
+                null as ReceiverParameterDescriptor?
         )
         propertyDescriptor.initialize(null, null)
 
@@ -138,7 +138,7 @@ public class LazyScriptClassMemberScope protected constructor(
                 parameter.getType(),
                 listOf(),
                 scriptDescriptor.getThisAsReceiverParameter(),
-                ReceiverParameterDescriptor.NO_RECEIVER_PARAMETER
+                null as ReceiverParameterDescriptor?
         )
         propertyDescriptor.initialize(null, null)
         return propertyDescriptor

compiler/frontend/src/org/jetbrains/kotlin/types/expressions/BasicExpressionTypingVisitor.java

@@ -68,7 +68,6 @@ import java.util.Collections;
 import java.util.Iterator;
 import java.util.List;
 
-import static org.jetbrains.kotlin.descriptors.ReceiverParameterDescriptor.NO_RECEIVER_PARAMETER;
 import static org.jetbrains.kotlin.diagnostics.Errors.*;
 import static org.jetbrains.kotlin.lexer.JetTokens.AS_KEYWORD;
 import static org.jetbrains.kotlin.lexer.JetTokens.AS_SAFE;
@@ -446,13 +445,13 @@ public class BasicExpressionTypingVisitor extends ExpressionTypingVisitor {
                 ReceiverParameterDescriptor receiverParameterDescriptor = resolutionResult.getReceiverParameterDescriptor();
                 recordThisOrSuperCallInTraceAndCallExtension(context, receiverParameterDescriptor, expression);
                 if (onlyClassReceivers && !isDeclaredInClass(receiverParameterDescriptor)) {
-                    return LabelResolver.LabeledReceiverResolutionResult.labelResolutionSuccess(NO_RECEIVER_PARAMETER);
+                    return LabelResolver.LabeledReceiverResolutionResult.labelResolutionSuccess(null);
                 }
             }
             return resolutionResult;
         }
         else {
-            ReceiverParameterDescriptor result = NO_RECEIVER_PARAMETER;
+            ReceiverParameterDescriptor result = null;
             List<ReceiverParameterDescriptor> receivers = context.scope.getImplicitReceiversHierarchy();
             if (onlyClassReceivers) {
                 for (ReceiverParameterDescriptor receiver : receivers) {
@@ -465,7 +464,7 @@ public class BasicExpressionTypingVisitor extends ExpressionTypingVisitor {
             else if (!receivers.isEmpty()) {
                 result = receivers.get(0);
             }
-            if (result != NO_RECEIVER_PARAMETER) {
+            if (result != null) {
                 context.trace.record(REFERENCE_TARGET, expression.getInstanceReference(), result.getContainingDeclaration());
                 recordThisOrSuperCallInTraceAndCallExtension(context, result, expression);
             }

compiler/frontend/src/org/jetbrains/kotlin/types/expressions/ControlStructureTypingUtils.java

@@ -119,7 +119,7 @@ public class ControlStructureTypingUtils {
         }
         function.initialize(
                 null,
-                ReceiverParameterDescriptor.NO_RECEIVER_PARAMETER,
+                null,
                 Lists.newArrayList(typeParameter),
                 valueParameters,
                 type,

core/descriptors/src/org/jetbrains/kotlin/descriptors/ReceiverParameterDescriptor.java

@@ -23,10 +23,6 @@ import org.jetbrains.kotlin.types.TypeSubstitutor;
 
 public interface ReceiverParameterDescriptor extends ParameterDescriptor {
 
-    // This field exists for better readability of the client code
-    @Nullable
-    ReceiverParameterDescriptor NO_RECEIVER_PARAMETER = null;
-
     @NotNull
     ReceiverValue getValue();
 

core/descriptors/src/org/jetbrains/kotlin/descriptors/impl/ConstructorDescriptorImpl.java

@@ -26,8 +26,6 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
 
-import static org.jetbrains.kotlin.descriptors.ReceiverParameterDescriptor.NO_RECEIVER_PARAMETER;
-
 public class ConstructorDescriptorImpl extends FunctionDescriptorImpl implements ConstructorDescriptor {
 
     protected final boolean isPrimary;
@@ -74,7 +72,7 @@ public class ConstructorDescriptorImpl extends FunctionDescriptorImpl implements
                 return ((ClassDescriptor) classContainer).getThisAsReceiverParameter();
             }
         }
-        return NO_RECEIVER_PARAMETER;
+        return null;
     }
 
     @NotNull

core/descriptors/src/org/jetbrains/kotlin/descriptors/impl/VariableDescriptorImpl.java

@@ -89,12 +89,12 @@ public abstract class VariableDescriptorImpl extends DeclarationDescriptorNonRoo
 
     @Override
     public ReceiverParameterDescriptor getExtensionReceiverParameter() {
-        return ReceiverParameterDescriptor.NO_RECEIVER_PARAMETER;
+        return null;
     }
 
     @Override
     public ReceiverParameterDescriptor getDispatchReceiverParameter() {
-        return ReceiverParameterDescriptor.NO_RECEIVER_PARAMETER;
+        return null;
     }
 
     @NotNull

core/descriptors/src/org/jetbrains/kotlin/resolve/DescriptorFactory.java

@@ -28,7 +28,6 @@ import org.jetbrains.kotlin.types.Variance;
 
 import java.util.Collections;
 
-import static org.jetbrains.kotlin.descriptors.ReceiverParameterDescriptor.NO_RECEIVER_PARAMETER;
 import static org.jetbrains.kotlin.resolve.DescriptorUtils.getDefaultConstructorVisibility;
 import static org.jetbrains.kotlin.resolve.descriptorUtil.DescriptorUtilPackage.getBuiltIns;
 
@@ -88,7 +87,7 @@ public class DescriptorFactory {
         SimpleFunctionDescriptorImpl values =
                 SimpleFunctionDescriptorImpl.create(enumClass, Annotations.EMPTY, DescriptorUtils.ENUM_VALUES,
                                                     CallableMemberDescriptor.Kind.SYNTHESIZED, enumClass.getSource());
-        return values.initialize(null, NO_RECEIVER_PARAMETER, Collections.<TypeParameterDescriptor>emptyList(),
+        return values.initialize(null, null, Collections.<TypeParameterDescriptor>emptyList(),
                                  Collections.<ValueParameterDescriptor>emptyList(),
                                  getBuiltIns(enumClass).getArrayType(Variance.INVARIANT, enumClass.getDefaultType()), Modality.FINAL,
                                  Visibilities.PUBLIC);
@@ -103,7 +102,7 @@ public class DescriptorFactory {
                 valueOf, null, 0, Annotations.EMPTY, Name.identifier("value"), getBuiltIns(enumClass).getStringType(), false, null,
                 enumClass.getSource()
         );
-        return valueOf.initialize(null, NO_RECEIVER_PARAMETER, Collections.<TypeParameterDescriptor>emptyList(),
+        return valueOf.initialize(null, null, Collections.<TypeParameterDescriptor>emptyList(),
                                   Collections.singletonList(parameterDescriptor), enumClass.getDefaultType(), Modality.FINAL,
                                   Visibilities.PUBLIC);
     }
@@ -114,7 +113,7 @@ public class DescriptorFactory {
             @Nullable JetType receiverParameterType
     ) {
         return receiverParameterType == null
-               ? NO_RECEIVER_PARAMETER
+               ? null
                : new ReceiverParameterDescriptorImpl(owner, new ExtensionReceiver(owner, receiverParameterType));
     }
 }

core/descriptors/src/org/jetbrains/kotlin/resolve/DescriptorUtils.java

@@ -46,7 +46,6 @@ import java.util.*;
 
 import static org.jetbrains.kotlin.builtins.KotlinBuiltIns.isAny;
 import static org.jetbrains.kotlin.descriptors.CallableMemberDescriptor.Kind.*;
-import static org.jetbrains.kotlin.descriptors.ReceiverParameterDescriptor.NO_RECEIVER_PARAMETER;
 import static org.jetbrains.kotlin.resolve.descriptorUtil.DescriptorUtilPackage.getBuiltIns;
 
 public class DescriptorUtils {
@@ -66,7 +65,7 @@ public class DescriptorUtils {
             ScriptDescriptor scriptDescriptor = (ScriptDescriptor) containingDeclaration;
             return scriptDescriptor.getThisAsReceiverParameter();
         }
-        return NO_RECEIVER_PARAMETER;
+        return null;
     }
 
     /**

core/descriptors/src/org/jetbrains/kotlin/types/ErrorUtils.java

@@ -416,7 +416,7 @@ public class ErrorUtils {
         );
         descriptor.setType(ERROR_PROPERTY_TYPE,
                            Collections.<TypeParameterDescriptor>emptyList(),
-                           ReceiverParameterDescriptor.NO_RECEIVER_PARAMETER,
+                           null,
                            (JetType) null
         );
 
@@ -428,7 +428,7 @@ public class ErrorUtils {
         ErrorSimpleFunctionDescriptorImpl function = new ErrorSimpleFunctionDescriptorImpl(ERROR_CLASS, ownerScope);
         function.initialize(
                 null,
-                ReceiverParameterDescriptor.NO_RECEIVER_PARAMETER,
+                null,
                 Collections.<TypeParameterDescriptorImpl>emptyList(), // TODO
                 Collections.<ValueParameterDescriptor>emptyList(), // TODO
                 createErrorType("<ERROR FUNCTION RETURN TYPE>"),