Implicit Nothing? type: don't report when declaration overrides nullable nothing type

#KT-30481 Fixed

idea/idea-core/src/org/jetbrains/kotlin/idea/core/psiModificationUtils.kt

@@ -354,12 +354,10 @@ fun KtDeclaration.isOverridable(): Boolean {
     }
 }
 
-fun KtDeclaration.getModalityFromDescriptor(): KtModifierKeywordToken? {
-    val descriptor = this.resolveToDescriptorIfAny()
+fun KtDeclaration.getModalityFromDescriptor(descriptor: DeclarationDescriptor? = resolveToDescriptorIfAny()): KtModifierKeywordToken? {
     if (descriptor is MemberDescriptor) {
         return mapModality(descriptor.modality)
     }
-
     return null
 }
 

idea/src/org/jetbrains/kotlin/idea/inspections/ImplicitNullableNothingTypeInspection.kt

@@ -16,21 +16,33 @@
 
 package org.jetbrains.kotlin.idea.inspections
 
+import org.jetbrains.kotlin.descriptors.CallableMemberDescriptor
+import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
+import org.jetbrains.kotlin.idea.caches.resolve.resolveToDescriptorIfAny
 import org.jetbrains.kotlin.idea.core.getModalityFromDescriptor
 import org.jetbrains.kotlin.idea.intentions.SpecifyTypeExplicitlyIntention
+import org.jetbrains.kotlin.idea.search.usagesSearch.descriptor
 import org.jetbrains.kotlin.lexer.KtTokens
 import org.jetbrains.kotlin.psi.KtCallableDeclaration
 import org.jetbrains.kotlin.psi.KtProperty
 import org.jetbrains.kotlin.types.typeUtil.isNullableNothing
 
 class ImplicitNullableNothingTypeInspection : IntentionBasedInspection<KtCallableDeclaration>(
-        intention = SpecifyTypeExplicitlyIntention::class,
-        additionalChecker = { declaration ->
-            SpecifyTypeExplicitlyIntention.getTypeForDeclaration(declaration).isNullableNothing() &&
-            (declaration.getModalityFromDescriptor() == KtTokens.OPEN_KEYWORD ||
-             declaration is KtProperty && declaration.isVar)
-        },
-        problemText = "Implicit `Nothing?` type"
+    intention = SpecifyTypeExplicitlyIntention::class,
+    additionalChecker = { declaration -> declaration.check() },
+    problemText = "Implicit `Nothing?` type"
 ) {
     override fun inspectionTarget(element: KtCallableDeclaration) = element.nameIdentifier
 }
+
+private fun KtCallableDeclaration.check(): Boolean {
+    if (!SpecifyTypeExplicitlyIntention.getTypeForDeclaration(this).isNullableNothing()) return false
+    val descriptor = this.resolveToDescriptorIfAny()
+    return (getModalityFromDescriptor(descriptor) == KtTokens.OPEN_KEYWORD || this is KtProperty && this.isVar) &&
+            !isOverridingNullableNothing(descriptor)
+}
+
+private fun KtCallableDeclaration.isOverridingNullableNothing(descriptor: DeclarationDescriptor?): Boolean {
+    return hasModifier(KtTokens.OVERRIDE_KEYWORD) &&
+            (descriptor as? CallableMemberDescriptor)?.overriddenDescriptors?.any { it.returnType?.isNullableNothing() == true } == true
+}

idea/testData/inspectionsLocal/implicitNullableNothingType/overrideFunction.kt

@@ -0,0 +1,7 @@
+abstract class Parent {
+    protected abstract fun foo(): String?
+}
+
+class Child : Parent() {
+    override fun <caret>foo() = null
+}

idea/testData/inspectionsLocal/implicitNullableNothingType/overrideFunction.kt.after

@@ -0,0 +1,7 @@
+abstract class Parent {
+    protected abstract fun foo(): String?
+}
+
+class Child : Parent() {
+    override fun foo(): Nothing? = null
+}

idea/testData/inspectionsLocal/implicitNullableNothingType/overrideNullableNothingFunction.kt

@@ -0,0 +1,9 @@
+// PROBLEM: none
+
+abstract class Parent {
+    protected abstract fun foo(): Nothing?
+}
+
+class Child : Parent() {
+    override fun <caret>foo() = null
+}

idea/testData/inspectionsLocal/implicitNullableNothingType/overrideNullableNothingProperty.kt

@@ -0,0 +1,9 @@
+// PROBLEM: none
+
+abstract class Parent {
+    abstract val foo: Nothing?
+}
+
+class Child : Parent() {
+    override val <caret>foo = null
+}

idea/testData/inspectionsLocal/implicitNullableNothingType/overrideProperty.kt

@@ -0,0 +1,7 @@
+abstract class Parent {
+    abstract val foo: Int?
+}
+
+class Child : Parent() {
+    override val <caret>foo = null
+}

idea/testData/inspectionsLocal/implicitNullableNothingType/overrideProperty.kt.after

@@ -0,0 +1,7 @@
+abstract class Parent {
+    abstract val foo: Int?
+}
+
+class Child : Parent() {
+    override val foo: Nothing? = null
+}

idea/tests/org/jetbrains/kotlin/idea/inspections/LocalInspectionTestGenerated.java

@@ -3271,7 +3271,7 @@ public class LocalInspectionTestGenerated extends AbstractLocalInspectionTest {
         }
     }
 
-    @TestMetadata("idea/testData/inspectionsLocal/ImplicitNullableNothingType")
+    @TestMetadata("idea/testData/inspectionsLocal/implicitNullableNothingType")
     @TestDataPath("$PROJECT_ROOT")
     @RunWith(JUnit3RunnerWithInners.class)
     public static class ImplicitNullableNothingType extends AbstractLocalInspectionTest {
@@ -3280,32 +3280,52 @@ public class LocalInspectionTestGenerated extends AbstractLocalInspectionTest {
         }
 
         public void testAllFilesPresentInImplicitNullableNothingType() throws Exception {
-            KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("idea/testData/inspectionsLocal/ImplicitNullableNothingType"), Pattern.compile("^([\\w\\-_]+)\\.(kt|kts)$"), TargetBackend.ANY, true);
+            KotlinTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("idea/testData/inspectionsLocal/implicitNullableNothingType"), Pattern.compile("^([\\w\\-_]+)\\.(kt|kts)$"), TargetBackend.ANY, true);
         }
 
         @TestMetadata("final.kt")
         public void testFinal() throws Exception {
-            runTest("idea/testData/inspectionsLocal/ImplicitNullableNothingType/final.kt");
+            runTest("idea/testData/inspectionsLocal/implicitNullableNothingType/final.kt");
         }
 
         @TestMetadata("function.kt")
         public void testFunction() throws Exception {
-            runTest("idea/testData/inspectionsLocal/ImplicitNullableNothingType/function.kt");
+            runTest("idea/testData/inspectionsLocal/implicitNullableNothingType/function.kt");
+        }
+
+        @TestMetadata("overrideFunction.kt")
+        public void testOverrideFunction() throws Exception {
+            runTest("idea/testData/inspectionsLocal/implicitNullableNothingType/overrideFunction.kt");
+        }
+
+        @TestMetadata("overrideNullableNothingFunction.kt")
+        public void testOverrideNullableNothingFunction() throws Exception {
+            runTest("idea/testData/inspectionsLocal/implicitNullableNothingType/overrideNullableNothingFunction.kt");
+        }
+
+        @TestMetadata("overrideNullableNothingProperty.kt")
+        public void testOverrideNullableNothingProperty() throws Exception {
+            runTest("idea/testData/inspectionsLocal/implicitNullableNothingType/overrideNullableNothingProperty.kt");
+        }
+
+        @TestMetadata("overrideProperty.kt")
+        public void testOverrideProperty() throws Exception {
+            runTest("idea/testData/inspectionsLocal/implicitNullableNothingType/overrideProperty.kt");
         }
 
         @TestMetadata("top.kt")
         public void testTop() throws Exception {
-            runTest("idea/testData/inspectionsLocal/ImplicitNullableNothingType/top.kt");
+            runTest("idea/testData/inspectionsLocal/implicitNullableNothingType/top.kt");
         }
 
         @TestMetadata("val.kt")
         public void testVal() throws Exception {
-            runTest("idea/testData/inspectionsLocal/ImplicitNullableNothingType/val.kt");
+            runTest("idea/testData/inspectionsLocal/implicitNullableNothingType/val.kt");
         }
 
         @TestMetadata("variable.kt")
         public void testVariable() throws Exception {
-            runTest("idea/testData/inspectionsLocal/ImplicitNullableNothingType/variable.kt");
+            runTest("idea/testData/inspectionsLocal/implicitNullableNothingType/variable.kt");
         }
     }