Data flow analysis: assignment of null makes variable effectively of type 'Nothing?'

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

@@ -144,9 +144,10 @@ internal class DelegatingDataFlowInfo private constructor(
         val newTypeInfo = newTypeInfo()
         var typesForB = getPredictableTypes(b)
         // Own type of B must be recorded separately, e.g. for a constant
-        // But if its type is the same as A or it's null, there is no reason to do it
-        // because usually null type or own type are not saved in this set
-        if (nullabilityOfB.canBeNonNull() && a.type != b.type) {
+        // But if its type is the same as A, there is no reason to do it
+        // because own type is not saved in this set
+        // Error types are also not saved
+        if (!b.type.isError && a.type != b.type) {
             typesForB += b.type
         }
         newTypeInfo.putAll(a, typesForB)

compiler/testData/diagnostics/tests/BinaryCallsOnNullableValues.kt

@@ -5,10 +5,10 @@ class A() {
 fun f(): Unit {
   var x: Int? = <!VARIABLE_WITH_REDUNDANT_INITIALIZER!>1<!>
   x = null
-  <!DEBUG_INFO_CONSTANT!>x<!> <!UNSAFE_INFIX_CALL!>+<!> 1
-  <!DEBUG_INFO_CONSTANT!>x<!> <!UNSAFE_INFIX_CALL, INFIX_MODIFIER_REQUIRED!>plus<!> 1
+  <!DEBUG_INFO_CONSTANT!>x<!> + 1
+  <!DEBUG_INFO_CONSTANT!>x<!> <!INFIX_MODIFIER_REQUIRED!>plus<!> 1
   <!DEBUG_INFO_CONSTANT!>x<!> <!UNSAFE_INFIX_CALL!><<!> 1
-  <!DEBUG_INFO_CONSTANT!>x<!> <!UNSAFE_INFIX_CALL!>+=<!> 1
+  <!TYPE_MISMATCH!><!DEBUG_INFO_CONSTANT!>x<!> += 1<!>
 
   <!DEBUG_INFO_CONSTANT!>x<!> == 1
   <!DEBUG_INFO_CONSTANT!>x<!> != 1

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

@@ -1,5 +1,5 @@
 fun foo(): Int {
     var i: Int? = <!VARIABLE_WITH_REDUNDANT_INITIALIZER!>42<!>
     i = null
-    return <!DEBUG_INFO_CONSTANT!>i<!> <!UNSAFE_INFIX_CALL!>+<!> 1
+    return <!TYPE_MISMATCH!><!DEBUG_INFO_CONSTANT!>i<!> + 1<!>
 }