Specify type: do not suggest nullable type if not null is overridden

So #KT-12814 Fixed

idea/src/org/jetbrains/kotlin/idea/intentions/SpecifyTypeExplicitlyIntention.kt

@@ -18,8 +18,10 @@ package org.jetbrains.kotlin.idea.intentions
 
 import com.intellij.codeInsight.intention.LowPriorityAction
 import com.intellij.codeInsight.template.*
+import com.intellij.openapi.application.ApplicationManager
 import com.intellij.openapi.editor.Editor
 import com.intellij.openapi.util.TextRange
+import com.intellij.psi.PsiComment
 import com.intellij.psi.PsiDocumentManager
 import org.jetbrains.kotlin.builtins.KotlinBuiltIns
 import org.jetbrains.kotlin.descriptors.CallableDescriptor
@@ -35,12 +37,10 @@ import org.jetbrains.kotlin.idea.util.application.runWriteAction
 import org.jetbrains.kotlin.idea.util.getResolutionScope
 import org.jetbrains.kotlin.idea.util.getResolvableApproximations
 import org.jetbrains.kotlin.psi.*
-import org.jetbrains.kotlin.psi.psiUtil.containingClassOrObject
-import org.jetbrains.kotlin.psi.psiUtil.endOffset
-import org.jetbrains.kotlin.psi.psiUtil.getElementTextWithContext
-import org.jetbrains.kotlin.psi.psiUtil.startOffset
+import org.jetbrains.kotlin.psi.psiUtil.*
 import org.jetbrains.kotlin.resolve.lazy.BodyResolveMode
 import org.jetbrains.kotlin.types.*
+import org.jetbrains.kotlin.types.typeUtil.makeNotNullable
 import org.jetbrains.kotlin.utils.ifEmpty
 
 class SpecifyTypeExplicitlyIntention :
@@ -102,7 +102,12 @@ class SpecifyTypeExplicitlyIntention :
 
         fun getTypeForDeclaration(declaration: KtCallableDeclaration): KotlinType {
             val descriptor = declaration.resolveToDescriptorIfAny()
-            val type = (descriptor as? CallableDescriptor)?.returnType
+            val type = (descriptor as? CallableDescriptor)?.let {
+                if (it.overriddenDescriptors.firstOrNull()?.returnType?.isMarkedNullable == false)
+                    it.returnType?.makeNotNullable()
+                else
+                    it.returnType
+            }
             if (type != null && type.isError && descriptor is PropertyDescriptor) {
                 return descriptor.setterType ?: ErrorUtils.createErrorType("null type")
             }
@@ -132,6 +137,16 @@ class SpecifyTypeExplicitlyIntention :
                 }
             }.ifEmpty { return null }
 
+            if (ApplicationManager.getApplication().isUnitTestMode) {
+                // This helps to be sure no nullable types are suggested
+                if (contextElement.containingKtFile.findDescendantOfType<PsiComment>()?.takeIf {
+                        it.text == "// CHOOSE_NULLABLE_TYPE_IF_EXISTS"
+                    } != null) {
+                    val targetType = types.firstOrNull { it.isMarkedNullable } ?: types.first()
+                    return TypeChooseValueExpression(listOf(targetType), targetType)
+                }
+            }
+
             return TypeChooseValueExpression(types, types.first())
         }
 

idea/testData/intentions/specifyTypeExplicitly/overrideNotNullFunction.kt

@@ -0,0 +1,9 @@
+// CHOOSE_NULLABLE_TYPE_IF_EXISTS
+// WITH_RUNTIME
+interface Base {
+    fun notNullFun(): String
+}
+
+class Tesst : Base {
+    override fun notNullFun()<caret> = java.lang.String.valueOf("")
+}

idea/testData/intentions/specifyTypeExplicitly/overrideNotNullFunction.kt.after

@@ -0,0 +1,9 @@
+// CHOOSE_NULLABLE_TYPE_IF_EXISTS
+// WITH_RUNTIME
+interface Base {
+    fun notNullFun(): String
+}
+
+class Tesst : Base {
+    override fun notNullFun(): String = java.lang.String.valueOf("")
+}

idea/testData/intentions/specifyTypeExplicitly/overrideNotNullProperty.kt

@@ -0,0 +1,9 @@
+// CHOOSE_NULLABLE_TYPE_IF_EXISTS
+// WITH_RUNTIME
+interface Base {
+    val notNull: String
+}
+
+class Tesst : Base {
+    override val notNull<caret> = java.lang.String.valueOf("")
+}

idea/testData/intentions/specifyTypeExplicitly/overrideNotNullProperty.kt.after

@@ -0,0 +1,9 @@
+// CHOOSE_NULLABLE_TYPE_IF_EXISTS
+// WITH_RUNTIME
+interface Base {
+    val notNull: String
+}
+
+class Tesst : Base {
+    override val notNull: String = java.lang.String.valueOf("")
+}

idea/testData/intentions/specifyTypeExplicitly/overrideNullableFunction.kt

@@ -0,0 +1,9 @@
+// CHOOSE_NULLABLE_TYPE_IF_EXISTS
+// WITH_RUNTIME
+interface Base {
+    fun nullableFun(): String?
+}
+
+class Tesst : Base {
+    override fun nullableFun()<caret> = java.lang.String.valueOf("")
+}

idea/testData/intentions/specifyTypeExplicitly/overrideNullableFunction.kt.after

@@ -0,0 +1,9 @@
+// CHOOSE_NULLABLE_TYPE_IF_EXISTS
+// WITH_RUNTIME
+interface Base {
+    fun nullableFun(): String?
+}
+
+class Tesst : Base {
+    override fun nullableFun(): String? = java.lang.String.valueOf("")
+}

idea/testData/intentions/specifyTypeExplicitly/overrideNullableProperty.kt

@@ -0,0 +1,9 @@
+// CHOOSE_NULLABLE_TYPE_IF_EXISTS
+// WITH_RUNTIME
+interface Base {
+    val nullable: String?
+}
+
+class Tesst : Base {
+    override val nullable<caret> = java.lang.String.valueOf("")
+}

idea/testData/intentions/specifyTypeExplicitly/overrideNullableProperty.kt.after

@@ -0,0 +1,9 @@
+// CHOOSE_NULLABLE_TYPE_IF_EXISTS
+// WITH_RUNTIME
+interface Base {
+    val nullable: String?
+}
+
+class Tesst : Base {
+    override val nullable: String? = java.lang.String.valueOf("")
+}

idea/tests/org/jetbrains/kotlin/idea/intentions/IntentionTestGenerated.java

@@ -14663,6 +14663,30 @@ public class IntentionTestGenerated extends AbstractIntentionTest {
             doTest(fileName);
         }
 
+        @TestMetadata("overrideNotNullFunction.kt")
+        public void testOverrideNotNullFunction() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/specifyTypeExplicitly/overrideNotNullFunction.kt");
+            doTest(fileName);
+        }
+
+        @TestMetadata("overrideNotNullProperty.kt")
+        public void testOverrideNotNullProperty() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/specifyTypeExplicitly/overrideNotNullProperty.kt");
+            doTest(fileName);
+        }
+
+        @TestMetadata("overrideNullableFunction.kt")
+        public void testOverrideNullableFunction() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/specifyTypeExplicitly/overrideNullableFunction.kt");
+            doTest(fileName);
+        }
+
+        @TestMetadata("overrideNullableProperty.kt")
+        public void testOverrideNullableProperty() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/specifyTypeExplicitly/overrideNullableProperty.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("propertyTypeFromGetter.kt")
         public void testPropertyTypeFromGetter() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/specifyTypeExplicitly/propertyTypeFromGetter.kt");