Make the soure generator format enums using their identifiers rather than numeric values.

src/libraries/System.Text.Json/gen/Helpers/SourceGeneratorHelpers.cs

@@ -0,0 +1,25 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Linq;
+using System.Collections.Generic;
+
+namespace System.Text.Json.SourceGeneration
+{
+    internal static class SourceGeneratorHelpers
+    {
+        private static readonly char[] s_enumSeparator = new char[] { ',' };
+
+        public static string FormatEnumLiteral<TEnum>(string fullyQualifiedName, TEnum value) where TEnum : struct, Enum
+        {
+            IEnumerable<string> values = value.ToString().Split(s_enumSeparator, StringSplitOptions.RemoveEmptyEntries)
+                .Select(name => name.Trim())
+                .Select(name =>
+                    int.TryParse(name, out _)
+                    ? $"({fullyQualifiedName})({name})"
+                    : $"{fullyQualifiedName}.{name}");
+
+            return string.Join(" | ", values);
+        }
+    }
+}

src/libraries/System.Text.Json/gen/JsonSourceGenerator.Emitter.cs

@@ -1211,23 +1211,16 @@ private SourceText GetPropertyNameInitialization(ContextGenerationSpec contextSp
                 return CompleteSourceFileAndReturnText(writer);
             }
 
-            private static string GetNumberHandlingAsStr(JsonNumberHandling? numberHandling) =>
-                numberHandling switch
-                {
-                    null => "null",
-                    >= 0 => $"({JsonNumberHandlingTypeRef}){(int)numberHandling.Value}",
-                    < 0 => $"({JsonNumberHandlingTypeRef})({(int)numberHandling.Value})"
-                };
+            private static string GetNumberHandlingAsStr(JsonNumberHandling? numberHandling)
+                => numberHandling.HasValue
+                ? SourceGeneratorHelpers.FormatEnumLiteral(JsonNumberHandlingTypeRef, numberHandling.Value)
+                : "null";
 
-            private static string GetObjectCreationHandlingAsStr(JsonObjectCreationHandling creationHandling) =>
-                creationHandling >= 0
-                ? $"({JsonObjectCreationHandlingTypeRef}){(int)creationHandling}"
-                : $"({JsonObjectCreationHandlingTypeRef})({(int)creationHandling})";
+            private static string GetObjectCreationHandlingAsStr(JsonObjectCreationHandling creationHandling)
+                => SourceGeneratorHelpers.FormatEnumLiteral(JsonObjectCreationHandlingTypeRef, creationHandling);
 
-            private static string GetUnmappedMemberHandlingAsStr(JsonUnmappedMemberHandling unmappedMemberHandling) =>
-                unmappedMemberHandling >= 0
-                ? $"({JsonUnmappedMemberHandlingTypeRef}){(int)unmappedMemberHandling}"
-                : $"({JsonUnmappedMemberHandlingTypeRef})({(int)unmappedMemberHandling})";
+            private static string GetUnmappedMemberHandlingAsStr(JsonUnmappedMemberHandling unmappedMemberHandling)
+                => SourceGeneratorHelpers.FormatEnumLiteral(JsonUnmappedMemberHandlingTypeRef, unmappedMemberHandling);
 
             private static string GetCreateValueInfoMethodRef(string typeCompilableName) => $"{CreateValueInfoMethodName}<{typeCompilableName}>";
 

src/libraries/System.Text.Json/gen/System.Text.Json.SourceGeneration.targets

@@ -49,6 +49,7 @@
     <Compile Include="..\Common\ThrowHelper.cs" Link="Common\System\Text\Json\ThrowHelper.cs" />
     <Compile Include="$(CommonPath)\Roslyn\GetBestTypeByMetadataName.cs" Link="Common\Roslyn\GetBestTypeByMetadataName.cs" />
     <Compile Include="Helpers\DiagnosticInfo.cs" />
+    <Compile Include="Helpers\SourceGeneratorHelpers.cs" />
     <Compile Include="Helpers\ImmutableEquatableArray.cs" />
     <Compile Include="Helpers\KnownTypeSymbols.cs" />
     <Compile Include="Helpers\RoslynExtensions.cs" />