Java to Kotlin converter: generate nullable type for private non-initialized fields

j2k/src/org/jetbrains/jet/j2k/ConstructorConverter.kt

@@ -116,7 +116,7 @@ class ConstructorConverter(private val converter: Converter) {
                 val (field, `type`) = parameterToField[parameter]!!
                 Parameter(field.declarationIdentifier(),
                           `type`,
-                          if (converter.isVal(field)) Parameter.VarValModifier.Val else Parameter.VarValModifier.Var,
+                          if (isVal(field)) Parameter.VarValModifier.Val else Parameter.VarValModifier.Var,
                           converter.convertAnnotations(parameter) + converter.convertAnnotations(field),
                           converter.convertModifiers(field).filter { it in ACCESS_MODIFIERS }).assignPrototypes(listOf(parameter, field), CommentsAndSpacesInheritance(blankLinesBefore = false))
             }

j2k/src/org/jetbrains/jet/j2k/Converter.kt

@@ -23,7 +23,6 @@ import java.util.*
 import com.intellij.psi.CommonClassNames.*
 import org.jetbrains.jet.lang.types.expressions.OperatorConventions.*
 import com.intellij.openapi.project.Project
-import com.intellij.psi.util.PsiUtil
 
 public trait ConversionScope {
     public fun contains(element: PsiElement): Boolean
@@ -235,14 +234,15 @@ public class Converter private(val project: Project, val settings: ConverterSett
             val typeToDeclare = variableTypeToDeclare(field,
                                                       settings.specifyFieldTypeByDefault || modifiers.isPublic || modifiers.isProtected,
                                                       isVal && modifiers.isPrivate)
+            val initializer = convertExpression(field.getInitializer(), field.getType())
             Field(name,
                   annotations,
                   modifiers,
                   typeToDeclare ?: typeConverter.convertVariableType(field),
-                  convertExpression(field.getInitializer(), field.getType()),
+                  initializer,
                   isVal,
                   typeToDeclare != null,
-                  field.hasWriteAccesses(field.getContainingClass()))
+                  initializer.isEmpty && shouldGenerateDefaultInitializer(field))
         }
         return converted.assignPrototype(field)
     }
@@ -264,27 +264,6 @@ public class Converter private(val project: Project, val settings: ConverterSett
         return if (convertedType == initializerType) null else convertedType
     }
 
-    fun isVal(field: PsiField): Boolean {
-        if (field.hasModifierProperty(PsiModifier.FINAL)) return true
-        if (!field.hasModifierProperty(PsiModifier.PRIVATE)) return false
-        val containingClass = field.getContainingClass() ?: return false
-        val writes = findVariableUsages(field, containingClass).filter { PsiUtil.isAccessedForWriting(it) }
-        if (writes.size == 0) return true
-        if (writes.size > 1) return false
-        val write = writes.single()
-        val parent = write.getParent()
-        if (parent is PsiAssignmentExpression &&
-                parent.getOperationSign().getTokenType() == JavaTokenType.EQ &&
-                isQualifierEmptyOrThis(write)) {
-            val constructor = write.getContainingConstructor()
-            return constructor != null &&
-                    constructor.getContainingClass() == containingClass &&
-                    parent.getParent() is PsiExpressionStatement &&
-                    parent.getParent()?.getParent() == constructor.getBody()
-        }
-        return false
-    }
-
     private fun convertMethod(method: PsiMethod, membersToRemove: MutableSet<PsiMember>): Member {
         return withMethodReturnType(method.getReturnType()).doConvertMethod(method, membersToRemove).assignPrototype(method)
     }

j2k/src/org/jetbrains/jet/j2k/TypeConverter.kt

@@ -120,6 +120,12 @@ class TypeConverter(val settings: ConverterSettings, val conversionScope: Conver
             return nullability
         }
 
+        if (nullability == Nullability.Default) {
+            if (variable is PsiField && variable.hasModifierProperty(PsiModifier.PRIVATE) && shouldGenerateDefaultInitializer(variable)) {
+                return Nullability.Nullable
+            }
+        }
+
         if (nullability == Nullability.Default) {
             val scope = searchScope(variable)
             if (scope != null) {

j2k/src/org/jetbrains/jet/j2k/Utils.kt

@@ -69,6 +69,30 @@ fun getDefaultInitializer(field: Field): Expression {
     return result.assignNoPrototype()
 }
 
+fun isVal(field: PsiField): Boolean {
+    if (field.hasModifierProperty(PsiModifier.FINAL)) return true
+    if (!field.hasModifierProperty(PsiModifier.PRIVATE)) return false
+    val containingClass = field.getContainingClass() ?: return false
+    val writes = findVariableUsages(field, containingClass).filter { PsiUtil.isAccessedForWriting(it) }
+    if (writes.size == 0) return true
+    if (writes.size > 1) return false
+    val write = writes.single()
+    val parent = write.getParent()
+    if (parent is PsiAssignmentExpression &&
+            parent.getOperationSign().getTokenType() == JavaTokenType.EQ &&
+            isQualifierEmptyOrThis(write)) {
+        val constructor = write.getContainingConstructor()
+        return constructor != null &&
+                constructor.getContainingClass() == containingClass &&
+                parent.getParent() is PsiExpressionStatement &&
+                parent.getParent()?.getParent() == constructor.getBody()
+    }
+    return false
+}
+
+fun shouldGenerateDefaultInitializer(field: PsiField)
+        = field.getInitializer() == null && !(isVal(field) && field.hasWriteAccesses(field.getContainingClass()))
+
 fun isQualifierEmptyOrThis(ref: PsiReferenceExpression): Boolean {
     val qualifier = ref.getQualifierExpression()
     return qualifier == null || (qualifier is PsiThisExpression && qualifier.getQualifier() == null)

j2k/src/org/jetbrains/jet/j2k/ast/Field.kt

@@ -26,7 +26,7 @@ class Field(
         val initializer: Element,
         val isVal: Boolean,
         val explicitType: Boolean,
-        private val hasWriteAccesses: Boolean
+        private val defaultInitializer: Boolean
 ) : Member(annotations, modifiers) {
 
     override fun generateCode(builder: CodeBuilder) {
@@ -40,7 +40,7 @@ class Field(
         }
 
         var initializerToUse = initializer
-        if (initializerToUse.isEmpty && !(isVal && hasWriteAccesses)) {
+        if (initializerToUse.isEmpty && defaultInitializer) {
             initializerToUse = getDefaultInitializer(this)
         }
         if (!initializerToUse.isEmpty) {

j2k/tests/testData/ast/enum/enumWithNameField.kt

@@ -1,4 +1,4 @@
 enum class E {
     I
-    private val name: String = 0
+    private val name: String? = null
 }

j2k/tests/testData/ast/field/classChildExtendsBase.kt

@@ -1,7 +1,7 @@
 class Base {
-    private val myFirst: String = 0
+    private val myFirst: String? = null
 }
 
 class Child : Base() {
-    private val mySecond: String = 0
+    private val mySecond: String? = null
 }

j2k/tests/testData/ast/field/privateField.kt

@@ -1,3 +1,3 @@
 class C {
-    private val f: Foo = 0
-}
+    private val f: Foo? = null
+}