[NI] Consider type non-nullable only if it has non-null supertype

Fixes #KT-12684 for NI

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/smartcasts/DataFlowInfoImpl.kt

@@ -250,7 +250,14 @@ internal class DataFlowInfoImpl private constructor(
         if (!value.type.isFlexible() && value.type.isSubtypeOf(type)) return this
 
         val nullabilityInfo = hashMapOf<DataFlowValue, Nullability>()
-        if (!type.isMarkedNullable) {
+
+        val isTypeNotNull =
+            if (languageVersionSettings.supportsFeature(LanguageFeature.NewInference))
+                !TypeUtils.isNullableType(type)
+            else
+                !type.isMarkedNullable
+
+        if (isTypeNotNull) {
             putNullabilityAndTypeInfo(nullabilityInfo, value, NOT_NULL, languageVersionSettings)
         }
 

compiler/testData/diagnostics/tests/generics/nullability/considerTypeNotNullOnlyIfItHasNotNullBound.kt

@@ -0,0 +1,6 @@
+// !LANGUAGE: +NewInference
+
+inline fun <T, reified S> foo(x: T?, y: T): T {
+    if (x is S) return <!TYPE_MISMATCH, TYPE_MISMATCH!>x<!>
+    return y
+}

compiler/testData/diagnostics/tests/generics/nullability/considerTypeNotNullOnlyIfItHasNotNullBound.txt

@@ -0,0 +1,3 @@
+package
+
+public inline fun </*0*/ T, /*1*/ reified S> foo(/*0*/ x: T?, /*1*/ y: T): T

compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestGenerated.java

@@ -8385,6 +8385,11 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
                     runTest("compiler/testData/diagnostics/tests/generics/nullability/capturedTypeWithPlatformSupertype.kt");
                 }
 
+                @TestMetadata("considerTypeNotNullOnlyIfItHasNotNullBound.kt")
+                public void testConsiderTypeNotNullOnlyIfItHasNotNullBound() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/generics/nullability/considerTypeNotNullOnlyIfItHasNotNullBound.kt");
+                }
+
                 @TestMetadata("correctSubstitutionForIncorporationConstraint.kt")
                 public void testCorrectSubstitutionForIncorporationConstraint() throws Exception {
                     runTest("compiler/testData/diagnostics/tests/generics/nullability/correctSubstitutionForIncorporationConstraint.kt");

compiler/tests/org/jetbrains/kotlin/checkers/javac/DiagnosticsUsingJavacTestGenerated.java

@@ -8385,6 +8385,11 @@ public class DiagnosticsUsingJavacTestGenerated extends AbstractDiagnosticsUsing
                     runTest("compiler/testData/diagnostics/tests/generics/nullability/capturedTypeWithPlatformSupertype.kt");
                 }
 
+                @TestMetadata("considerTypeNotNullOnlyIfItHasNotNullBound.kt")
+                public void testConsiderTypeNotNullOnlyIfItHasNotNullBound() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/generics/nullability/considerTypeNotNullOnlyIfItHasNotNullBound.kt");
+                }
+
                 @TestMetadata("correctSubstitutionForIncorporationConstraint.kt")
                 public void testCorrectSubstitutionForIncorporationConstraint() throws Exception {
                     runTest("compiler/testData/diagnostics/tests/generics/nullability/correctSubstitutionForIncorporationConstraint.kt");