adjust assert

Author: RikkiGibson

src/Compilers/CSharp/Portable/FlowAnalysis/NullableWalker.cs

@@ -9307,15 +9307,18 @@ private void TrackAnalyzedNullabilityThroughConversionGroup(TypeWithState result
                 Debug.Assert(conversionOpt.ConversionGroupOpt == conversionGroup);
                 // TODO2: here the visit result has reinferred nested nullability and we were throwing that away to use the conversion type from initial binding. why?
                 // it makes no sense for the visit result to be lacking information that the initial bound type actually has.
-                Debug.Assert(visitResult.LValueType.Type.Equals(conversionOpt.Type, TypeCompareKind.AllNullableIgnoreOptions));
-                //visitResult = withType(visitResult, conversionOpt.Type);
+                // TODO2: what does it mean for these types to differ? Why is it correct to copy over the top-level nullability when the types have differences beyond nullability?
+                if (!visitResult.LValueType.Type.Equals(conversionOpt.Type, TypeCompareKind.AllNullableIgnoreOptions))
+                {
+                    visitResult = withType(visitResult, conversionOpt.Type);
+                }
                 SetAnalyzedNullability(conversionOpt, visitResult);
                 conversionOpt = conversionOpt.Operand as BoundConversion;
             }
 
-            //static VisitResult withType(VisitResult visitResult, TypeSymbol newType) =>
-            //    new VisitResult(TypeWithState.Create(newType, visitResult.RValueType.State),
-            //                    TypeWithAnnotations.Create(newType, visitResult.LValueType.NullableAnnotation));
+            static VisitResult withType(VisitResult visitResult, TypeSymbol newType) =>
+                new VisitResult(TypeWithState.Create(newType, visitResult.RValueType.State),
+                                TypeWithAnnotations.Create(newType, visitResult.LValueType.NullableAnnotation));
         }
 
         /// <summary>

src/Compilers/CSharp/Test/Symbol/Symbols/Source/NullablePublicAPITests.cs

@@ -5435,7 +5435,7 @@ public void Repro_WithSwitchExpr()
                 #nullable enable
 
                 var b = false;
-                var arr = b switch { true => ["1", null], false => new[] { "2", null } };
+                var arr = b switch { true => ["1"], false => new[] { "2" } };
                 """;
 
             var comp = CreateCompilation(source);