Regression: correct smart cast from Type? to Type!

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

@@ -300,8 +300,8 @@ internal class DelegatingDataFlowInfo private constructor(
             val toDelete = newTypeInfo()
             for (value in typeInfo.keys()) {
                 for (type in typeInfo[value]) {
-                    // Remove original type and for not flexible type also all its supertypes (see also KT-10666)
-                    if (if (value.type.isFlexible()) value.type == type else value.type.isSubtypeOf(type)) {
+                    // Remove original type (see also KT-10666)
+                    if (value.type == type) {
                         toDelete.put(value, type)
                     }
                 }

compiler/testData/diagnostics/tests/smartCasts/varnotnull/toFlexibleType.kt

@@ -0,0 +1,16 @@
+// FILE: J.java
+
+class J {
+    static String foo() { return "abc"; }
+}
+
+// FILE: test.kt
+
+fun bar() {
+    var v: String?
+    v = J.foo()
+    <!DEBUG_INFO_SMARTCAST!>v<!>.length
+    gav(<!DEBUG_INFO_SMARTCAST!>v<!>)
+}
+
+fun gav(v: String) = v

compiler/testData/diagnostics/tests/smartCasts/varnotnull/toFlexibleType.txt

@@ -0,0 +1,14 @@
+package
+
+public fun bar(): kotlin.Unit
+public fun gav(/*0*/ v: kotlin.String): kotlin.String
+
+public/*package*/ open class J {
+    public/*package*/ constructor J()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+    // Static members
+    public/*package*/ open fun foo(): kotlin.String!
+}

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

@@ -17435,6 +17435,12 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
                     doTest(fileName);
                 }
 
+                @TestMetadata("toFlexibleType.kt")
+                public void testToFlexibleType() throws Exception {
+                    String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/smartCasts/varnotnull/toFlexibleType.kt");
+                    doTest(fileName);
+                }
+
                 @TestMetadata("unnecessary.kt")
                 public void testUnnecessary() throws Exception {
                     String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/smartCasts/varnotnull/unnecessary.kt");