Refactor external overidability conditions

Before this change they could only negatively affect on result
Now they may force success result

Also refine overridavility condition for java fields:
two java fields having the same name are seen as overrides even
if they have different type

core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/FieldOverridabilityCondition.kt

@@ -20,11 +20,16 @@ import org.jetbrains.kotlin.descriptors.CallableDescriptor
 import org.jetbrains.kotlin.descriptors.PropertyDescriptor
 import org.jetbrains.kotlin.load.java.lazy.descriptors.isJavaField
 import org.jetbrains.kotlin.resolve.ExternalOverridabilityCondition
+import org.jetbrains.kotlin.resolve.ExternalOverridabilityCondition.Result
 
 class FieldOverridabilityCondition : ExternalOverridabilityCondition {
-    override fun isOverridable(superDescriptor: CallableDescriptor, subDescriptor: CallableDescriptor): Boolean {
-        if (subDescriptor !is PropertyDescriptor || superDescriptor !is PropertyDescriptor) return true
+    override fun isOverridable(superDescriptor: CallableDescriptor, subDescriptor: CallableDescriptor): Result {
+        if (subDescriptor !is PropertyDescriptor || superDescriptor !is PropertyDescriptor) return Result.UNKNOWN
+        if (subDescriptor.name != superDescriptor.name) return Result.UNKNOWN
 
-        return subDescriptor.isJavaField == superDescriptor.isJavaField
+        if (subDescriptor.isJavaField && superDescriptor.isJavaField) return Result.OVERRIDABLE
+        if (subDescriptor.isJavaField || superDescriptor.isJavaField) return Result.INCOMPATIBLE
+
+        return Result.UNKNOWN
     }
 }

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

@@ -20,5 +20,10 @@ import org.jetbrains.annotations.NotNull;
 import org.jetbrains.kotlin.descriptors.CallableDescriptor;
 
 public interface ExternalOverridabilityCondition {
-    boolean isOverridable(@NotNull CallableDescriptor superDescriptor, @NotNull CallableDescriptor subDescriptor);
+    enum Result {
+        OVERRIDABLE, CONFLICT, INCOMPATIBLE, UNKNOWN
+    }
+
+    @NotNull
+    Result isOverridable(@NotNull CallableDescriptor superDescriptor, @NotNull CallableDescriptor subDescriptor);
 }

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

@@ -34,6 +34,7 @@ import org.jetbrains.kotlin.types.checker.KotlinTypeChecker;
 import java.util.*;
 
 import static org.jetbrains.kotlin.resolve.OverridingUtil.OverrideCompatibilityInfo.Result.*;
+import static org.jetbrains.kotlin.resolve.OverridingUtil.OverrideCompatibilityInfo.Result.INCOMPATIBLE;
 
 public class OverridingUtil {
 
@@ -76,6 +77,30 @@ public class OverridingUtil {
             @NotNull CallableDescriptor superDescriptor,
             @NotNull CallableDescriptor subDescriptor,
             boolean checkReturnType
+    ) {
+        for (ExternalOverridabilityCondition externalCondition : EXTERNAL_CONDITIONS) {
+            ExternalOverridabilityCondition.Result result = externalCondition.isOverridable(superDescriptor, subDescriptor);
+            switch (result) {
+                case OVERRIDABLE:
+                    return OverrideCompatibilityInfo.success();
+                case CONFLICT:
+                    return OverrideCompatibilityInfo.conflict("External condition failed");
+                case INCOMPATIBLE:
+                    return OverrideCompatibilityInfo.incompatible("External condition");
+                case UNKNOWN:
+                    // do nothing
+                    // go to the next external condition or default override check
+            }
+        }
+
+        return isOverridableByWithoutExternalConditions(superDescriptor, subDescriptor, checkReturnType);
+    }
+
+    @NotNull
+    public OverrideCompatibilityInfo isOverridableByWithoutExternalConditions(
+            @NotNull CallableDescriptor superDescriptor,
+            @NotNull CallableDescriptor subDescriptor,
+            boolean checkReturnType
     ) {
         if (superDescriptor instanceof FunctionDescriptor && !(subDescriptor instanceof FunctionDescriptor) ||
             superDescriptor instanceof PropertyDescriptor && !(subDescriptor instanceof PropertyDescriptor)) {
@@ -138,12 +163,6 @@ public class OverridingUtil {
             }
         }
 
-        for (ExternalOverridabilityCondition externalCondition : EXTERNAL_CONDITIONS) {
-            if (!externalCondition.isOverridable(superDescriptor, subDescriptor)) {
-                return OverrideCompatibilityInfo.incompatible("External condition failed");
-            }
-        }
-
         return OverrideCompatibilityInfo.success();
     }