Minor, extracted TypeUtils.isTypeParameter

compiler/frontend/src/org/jetbrains/jet/lang/types/CastDiagnosticsUtil.java

@@ -47,7 +47,7 @@ public class CastDiagnosticsUtil {
         if (isRelated(lhsType, rhsType, platformToKotlinClassMap)) return true;
         // This is an oversimplification (which does not render the method incomplete):
         // we consider any type parameter capable of taking any value, which may be made more precise if we considered bounds
-        if (isTypeParameter(lhsType) || isTypeParameter(rhsType)) return true;
+        if (TypeUtils.isTypeParameter(lhsType) || TypeUtils.isTypeParameter(rhsType)) return true;
         if (isFinal(lhsType) || isFinal(rhsType)) return false;
         if (isTrait(lhsType) || isTrait(rhsType)) return true;
         return false;
@@ -97,10 +97,6 @@ public class CastDiagnosticsUtil {
         return result;
     }
 
-    private static boolean isTypeParameter(@NotNull JetType type) {
-        return type.getConstructor().getDeclarationDescriptor() instanceof TypeParameterDescriptor;
-    }
-
     private static boolean isFinal(@NotNull JetType type) {
         return !TypeUtils.canHaveSubtypes(JetTypeChecker.DEFAULT, type);
     }
@@ -124,7 +120,7 @@ public class CastDiagnosticsUtil {
         if (typeChecker.isSubtypeOf(supertype, subtype)) return false;
 
         // downcasting to a type parameter is always erased
-        if (isTypeParameter(subtype)) return true;
+        if (TypeUtils.isTypeParameter(subtype)) return true;
 
         // Check that we are actually casting to a generic type
         // NOTE: this does not account for 'as Array<List<T>>'

core/descriptors/src/org/jetbrains/jet/lang/types/TypeUtils.java

@@ -434,7 +434,7 @@ public class TypeUtils {
         if (TypesPackage.isFlexible(type) && isNullableType(TypesPackage.flexibility(type).getUpperBound())) {
             return true;
         }
-        if (type.getConstructor().getDeclarationDescriptor() instanceof TypeParameterDescriptor) {
+        if (isTypeParameter(type)) {
             return hasNullableSuperType(type);
         }
         return false;
@@ -720,6 +720,18 @@ public class TypeUtils {
         });
     }
 
+    public static boolean isTypeParameter(@NotNull JetType type) {
+        return getTypeParameterDescriptorOrNull(type) != null;
+    }
+
+    @Nullable
+    public static TypeParameterDescriptor getTypeParameterDescriptorOrNull(@NotNull JetType type) {
+        if (type.getConstructor().getDeclarationDescriptor() instanceof TypeParameterDescriptor) {
+            return (TypeParameterDescriptor) type.getConstructor().getDeclarationDescriptor();
+        }
+        return null;
+    }
+
     private static abstract class AbstractTypeWithKnownNullability extends AbstractJetType {
         private final JetType delegate;