Address review feedback

src/libraries/System.Text.Json/Common/JsonSerializableAttribute.cs

@@ -36,7 +36,8 @@ public JsonSerializableAttribute(Type type) { }
         public string? TypeInfoPropertyName { get; set; }
 
         /// <summary>
-        /// Determines what the source generator should generate for the type.
+        /// Determines what the source generator should generate for the type. If the value is <see cref="JsonSourceGenerationMode.Default"/>,
+        /// then the setting specified on <see cref="JsonSourceGenerationOptionsAttribute.GenerationMode"/> will be used.
         /// </summary>
         public JsonSourceGenerationMode GenerationMode { get; set; }
     }

src/libraries/System.Text.Json/Common/JsonSourceGenerationMode.cs

@@ -15,9 +15,11 @@ namespace System.Text.Json.Serialization
     enum JsonSourceGenerationMode
     {
         /// <summary>
-        /// Unspecified source generation mode.
+        /// When specified on <see cref="JsonSourceGenerationOptionsAttribute.GenerationMode"/>, indicates that both type-metadata initialization logic
+        /// and optimized serialization logic should be generated for all types. When specified on <see cref="JsonSerializableAttribute.GenerationMode"/>,
+        /// indicates that the setting on <see cref="JsonSourceGenerationOptionsAttribute.GenerationMode"/> should be used.
         /// </summary>
-        Unspecified = 0,
+        Default = 0,
 
         /// <summary>
         /// Instructs the JSON source generator to generate type-metadata initialization logic.
@@ -28,7 +30,7 @@ enum JsonSourceGenerationMode
         Metadata = 1,
 
         /// <summary>
-        /// Instructs the JSON source generator to generate serialization logic.
+        /// Instructs the JSON source generator to generate optimized serialization logic.
         /// </summary>
         /// <remarks>
         /// This mode supports only a subset of <see cref="JsonSerializer"/> features.

src/libraries/System.Text.Json/Common/JsonSourceGenerationOptionsAttribute.cs

@@ -51,8 +51,8 @@ class JsonSourceGenerationOptionsAttribute : JsonAttribute
         public bool WriteIndented { get; set; }
 
         /// <summary>
-        /// Specifies the source generation mode.
+        /// Specifies the source generation mode for types that don't explicitly set the mode with <see cref="JsonSerializableAttribute.GenerationMode"/>.
         /// </summary>
-        public JsonSourceGenerationMode GenerationMode { get; set; } = JsonSourceGenerationMode.Metadata | JsonSourceGenerationMode.Serialization;
+        public JsonSourceGenerationMode GenerationMode { get; set; }
     }
 }

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

@@ -310,18 +310,19 @@ private static bool TryGetClassDeclarationList(INamedTypeSymbol typeSymbol, [Not
                         NameEqualsSyntax? propertyNameNode = childNodes.First() as NameEqualsSyntax;
                         Debug.Assert(propertyNameNode != null);
 
-                        SyntaxNode? propertyValueMode = childNodes.ElementAtOrDefault(1);
+                        SyntaxNode? propertyValueNode = childNodes.ElementAtOrDefault(1);
                         string optionName = propertyNameNode.Name.Identifier.ValueText;
 
                         if (optionName == nameof(JsonSerializableAttribute.TypeInfoPropertyName))
                         {
-                            typeInfoPropertyName = propertyValueMode.GetFirstToken().ValueText;
+                            typeInfoPropertyName = propertyValueNode.GetFirstToken().ValueText;
                         }
                         else if (optionName == nameof(JsonSerializableAttribute.GenerationMode))
                         {
-                            if (Enum.TryParse<JsonSourceGenerationMode>(propertyValueMode.GetLastToken().ValueText, out JsonSourceGenerationMode value))
+                            JsonSourceGenerationMode? mode = GetJsonSourceGenerationModeEnumVal(propertyValueNode);
+                            if (mode.HasValue)
                             {
-                                generationMode = value;
+                                generationMode = mode.Value;
                             }
                         }
                     }
@@ -348,10 +349,10 @@ private static bool TryGetClassDeclarationList(INamedTypeSymbol typeSymbol, [Not
                     typeGenerationSpec.TypeInfoPropertyName = typeInfoPropertyName;
                 }
 
-                ClassType classType = typeGenerationSpec.ClassType;
-                CollectionType collectionType = typeGenerationSpec.CollectionType;
                 switch (generationMode)
                 {
+                    case JsonSourceGenerationMode.Default:
+                        break;
                     case JsonSourceGenerationMode.Metadata | JsonSourceGenerationMode.Serialization:
                         typeGenerationSpec.GenerateSerializationLogic = typeGenerationSpec.FastPathIsSupported();
                         typeGenerationSpec.GenerateMetadata = true;
@@ -371,6 +372,24 @@ private static bool TryGetClassDeclarationList(INamedTypeSymbol typeSymbol, [Not
                 return typeGenerationSpec;
             }
 
+            private static JsonSourceGenerationMode? GetJsonSourceGenerationModeEnumVal(SyntaxNode propertyValueMode)
+            {
+                IEnumerable<string> enumTokens = propertyValueMode
+                    .DescendantTokens()
+                    .Where(token => IsValidEnumIdentifier(token.ValueText))
+                    .Select(token => token.ValueText);
+                string enumAsStr = string.Join(",", enumTokens);
+
+                if (Enum.TryParse<JsonSourceGenerationMode>(enumAsStr, out JsonSourceGenerationMode value))
+                {
+                    return value;
+                }
+
+                return null;
+
+                static bool IsValidEnumIdentifier(string token) => token != nameof(JsonSourceGenerationMode) && token != "." && token != "|";
+            }
+
             private static JsonSourceGenerationOptionsAttribute? GetSerializerOptions(AttributeSyntax? attributeSyntax)
             {
                 if (attributeSyntax == null)
@@ -452,9 +471,10 @@ private static bool TryGetClassDeclarationList(INamedTypeSymbol typeSymbol, [Not
                             break;
                         case nameof(JsonSourceGenerationOptionsAttribute.GenerationMode):
                             {
-                                if (Enum.TryParse<JsonSourceGenerationMode>(propertyValueStr, out JsonSourceGenerationMode value))
+                                JsonSourceGenerationMode? mode = GetJsonSourceGenerationModeEnumVal(propertyValueNode);
+                                if (mode.HasValue)
                                 {
-                                    options.GenerationMode = value;
+                                    options.GenerationMode = mode.Value;
                                 }
                             }
                             break;

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

@@ -33,7 +33,6 @@ public void Initialize(GeneratorInitializationContext context)
         /// <param name="executionContext"></param>
         public void Execute(GeneratorExecutionContext executionContext)
         {
-            //if (!Diagnostics.Debugger.IsAttached) { Diagnostics.Debugger.Launch(); };
             SyntaxReceiver receiver = (SyntaxReceiver)executionContext.SyntaxReceiver;
             List<ClassDeclarationSyntax>? contextClasses = receiver.ClassDeclarationSyntaxList;
             if (contextClasses == null)

src/libraries/System.Text.Json/gen/TypeGenerationSpec.cs

@@ -28,15 +28,15 @@ internal class TypeGenerationSpec
         private bool? _generateMetadata;
         public bool GenerateMetadata
         {
-            get => _generateMetadata ??= (JsonSourceGenerationMode.Metadata & _generationMode) != 0;
+            get => _generateMetadata ??= GenerationModeIsSpecified(JsonSourceGenerationMode.Metadata);
             // Optionally set during type metadata computation.
             set => _generateMetadata = value;
         }
 
         private bool? _generateSerializationLogic;
         public bool GenerateSerializationLogic
         {
-            get => _generateSerializationLogic ??= ((JsonSourceGenerationMode.Serialization & _generationMode) != 0) && FastPathIsSupported();
+            get => _generateSerializationLogic ??= GenerationModeIsSpecified(JsonSourceGenerationMode.Serialization) && FastPathIsSupported();
             // Optionally set during type metadata computation.
             set => _generateSerializationLogic = value;
         }
@@ -117,5 +117,7 @@ public bool FastPathIsSupported()
 
             return false;
         }
+
+        private bool GenerationModeIsSpecified(JsonSourceGenerationMode mode) => _generationMode == JsonSourceGenerationMode.Default || (mode & _generationMode) != 0;
     }
 }

src/libraries/System.Text.Json/ref/System.Text.Json.cs

@@ -831,7 +831,7 @@ public JsonSourceGenerationOptionsAttribute() { }
     [System.FlagsAttribute]
     public enum JsonSourceGenerationMode
     {
-        Unspecified = 0,
+        Default = 0,
         Metadata = 1,
         Serialization = 2,
     }

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Tests/MixedModeContextTests.cs

@@ -14,7 +14,7 @@ namespace System.Text.Json.SourceGeneration.Tests
     [JsonSerializable(typeof(WeatherForecastWithPOCOs), GenerationMode = JsonSourceGenerationMode.Metadata)]
     [JsonSerializable(typeof(EmptyPoco), GenerationMode = JsonSourceGenerationMode.Serialization)]
     [JsonSerializable(typeof(HighLowTemps), GenerationMode = JsonSourceGenerationMode.Serialization)]
-    [JsonSerializable(typeof(MyType), GenerationMode = JsonSourceGenerationMode.Metadata | JsonSourceGenerationMode.Serialization)]
+    [JsonSerializable(typeof(MyType), GenerationMode = JsonSourceGenerationMode.Default)]
     [JsonSerializable(typeof(MyType2), GenerationMode = JsonSourceGenerationMode.Metadata | JsonSourceGenerationMode.Serialization)]
     [JsonSerializable(typeof(MyIntermediateType), GenerationMode = JsonSourceGenerationMode.Metadata | JsonSourceGenerationMode.Serialization)]
     [JsonSerializable(typeof(HighLowTempsImmutable), GenerationMode = JsonSourceGenerationMode.Metadata)]
@@ -83,7 +83,6 @@ public override void RoundTripCollectionsDictionary()
         {
             WeatherForecastWithPOCOs expected = CreateWeatherForecastWithPOCOs();
 
-            if (!Diagnostics.Debugger.IsAttached) { Diagnostics.Debugger.Launch(); };
             string json = JsonSerializer.Serialize(expected, DefaultContext.WeatherForecastWithPOCOs);
             JsonTestHelper.AssertThrows_PropMetadataInit(() => JsonSerializer.Deserialize(json, DefaultContext.WeatherForecastWithPOCOs), typeof(HighLowTemps));