Override/Implement: Make return type non-nullable (platform collection case) when overriding Java method

#KT-13455 Fixed

ChangeLog.md

@@ -172,6 +172,7 @@ These artifacts include extensions for the types available in the latter JDKs, s
 - [`KT-13207`](https://youtrack.jetbrains.com/issue/KT-13207) Exception on safe delete from intention in 2016.2
 - [`KT-12887`](https://youtrack.jetbrains.com/issue/KT-12887) "Extend selection" should select call's invoked expression
 - [`KT-6520`](https://youtrack.jetbrains.com/issue/KT-6520) Introduce 'maino' and 'psvmo' templates for generating main in object
+- [`KT-13455`](https://youtrack.jetbrains.com/issue/KT-13455) Override/Implement: Make return type non-nullable (platform collection case) when overriding Java method
 - Fix exception when choose Gradle configurer after project is synced
 - Allow configuring Kotlin in Gradle module without Kotlin sources
 - Show all Kotlin annotations when browsing hierarchy of "java.lang.Annotation"

idea/ide-common/src/org/jetbrains/kotlin/idea/util/TypeUtils.kt

@@ -34,12 +34,18 @@ import org.jetbrains.kotlin.types.typeUtil.*
 import org.jetbrains.kotlin.utils.SmartSet
 import org.jetbrains.kotlin.utils.addToStdlib.singletonList
 
-fun KotlinType.approximateFlexibleTypes(preferNotNull: Boolean = false): KotlinType {
+fun KotlinType.approximateFlexibleTypes(
+        preferNotNull: Boolean = false,
+        preferStarForRaw: Boolean = false
+): KotlinType {
     if (isDynamic()) return this
-    return approximateNonDynamicFlexibleTypes(preferNotNull)
+    return approximateNonDynamicFlexibleTypes(preferNotNull, preferStarForRaw)
 }
 
-private fun KotlinType.approximateNonDynamicFlexibleTypes(preferNotNull: Boolean = false): SimpleType {
+private fun KotlinType.approximateNonDynamicFlexibleTypes(
+        preferNotNull: Boolean = false,
+        preferStarForRaw: Boolean = false
+): SimpleType {
     if (isFlexible()) {
         val flexible = asFlexibleType()
         val lowerClass = flexible.lowerBound.constructor.declarationDescriptor as? ClassDescriptor?
@@ -51,6 +57,8 @@ private fun KotlinType.approximateNonDynamicFlexibleTypes(preferNotNull: Boolean
         var approximation =
                 if (isCollection)
                     (if (isAnnotatedReadOnly()) flexible.upperBound else flexible.lowerBound).makeNullableAsSpecified(!preferNotNull)
+                else
+                    if (this is RawType && preferStarForRaw) flexible.upperBound.makeNullableAsSpecified(!preferNotNull)
                 else
                     if (preferNotNull) flexible.lowerBound else flexible.upperBound
 

idea/idea-core/src/org/jetbrains/kotlin/idea/core/overrideImplement/OverrideMemberChooserObject.kt

@@ -31,13 +31,11 @@ import org.jetbrains.kotlin.idea.core.util.DescriptorMemberChooserObject
 import org.jetbrains.kotlin.idea.j2k.IdeaDocCommentConverter
 import org.jetbrains.kotlin.idea.kdoc.KDocElementFactory
 import org.jetbrains.kotlin.idea.util.IdeDescriptorRenderers
+import org.jetbrains.kotlin.idea.util.approximateFlexibleTypes
 import org.jetbrains.kotlin.psi.*
 import org.jetbrains.kotlin.psi.findDocComment.findDocComment
 import org.jetbrains.kotlin.renderer.*
 import org.jetbrains.kotlin.resolve.descriptorUtil.setSingleOverridden
-import org.jetbrains.kotlin.types.KotlinType
-import org.jetbrains.kotlin.types.isFlexible
-import org.jetbrains.kotlin.types.typeUtil.makeNotNullable
 
 interface OverrideMemberChooserObject : ClassMember {
     enum class BodyType {
@@ -161,10 +159,7 @@ private fun generateConstructorParameter(project: Project, descriptor: PropertyD
 private fun generateFunction(project: Project, descriptor: FunctionDescriptor, bodyType: OverrideMemberChooserObject.BodyType): KtNamedFunction {
     val newDescriptor = object : FunctionDescriptor by descriptor {
         override fun getModality() = Modality.OPEN
-        override fun getReturnType(): KotlinType? {
-            val originalType = descriptor.returnType ?: return null
-            return if (originalType.isFlexible()) originalType.makeNotNullable() else originalType
-        }
+        override fun getReturnType() = descriptor.returnType?.approximateFlexibleTypes(preferNotNull = true, preferStarForRaw = true)
         override fun getOverriddenDescriptors() = listOf(descriptor)
         override fun <R : Any?, D : Any?> accept(visitor: DeclarationDescriptorVisitor<R, D>, data: D) = visitor.visitFunctionDescriptor(this, data)
     }

idea/testData/codeInsight/overrideImplement/platformCollectionTypes/foo/A.java

@@ -0,0 +1,7 @@
+package foo;
+
+import java.util.List;
+
+public interface A {
+    List<String> foo();
+}

idea/testData/codeInsight/overrideImplement/platformCollectionTypes/foo/Impl.kt

@@ -0,0 +1,5 @@
+import foo.A
+
+class B : A {
+    <caret>
+}

idea/testData/codeInsight/overrideImplement/platformCollectionTypes/foo/Impl.kt.after

@@ -0,0 +1,7 @@
+import foo.A
+
+class B : A {
+    override fun foo(): MutableList<String> {
+        <selection><caret>TODO("not implemented") //To change body of created functions use File | Settings | File Templates.</selection>
+    }
+}

idea/tests/org/jetbrains/kotlin/idea/codeInsight/OverrideImplementTest.kt

@@ -248,6 +248,10 @@ class OverrideImplementTest : AbstractOverrideImplementTest() {
         doOverrideDirectoryTest("foo")
     }
 
+    fun testPlatformCollectionTypes() {
+        doOverrideDirectoryTest("foo")
+    }
+
     fun testNullableJavaType() {
         doOverrideDirectoryTest("foo")
     }