Expose the feature switch as a property on JsonSerializer -- rename f…

…eature switch to match namespace.

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

@@ -280,6 +280,7 @@ public static partial class JsonSerializer
         [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("JSON serialization and deserialization might require types that cannot be statically analyzed. Use the overload that takes a JsonTypeInfo or JsonSerializerContext, or make sure all of the required types are preserved.")]
         public static TValue? Deserialize<TValue>(ref System.Text.Json.Utf8JsonReader reader, System.Text.Json.JsonSerializerOptions? options = null) { throw null; }
         public static TValue? Deserialize<TValue>(ref System.Text.Json.Utf8JsonReader reader, System.Text.Json.Serialization.Metadata.JsonTypeInfo<TValue> jsonTypeInfo) { throw null; }
+        public static bool IsReflectionEnabledByDefault { get { throw null; } }
         public static void Serialize(System.IO.Stream utf8Json, object? value, System.Text.Json.Serialization.Metadata.JsonTypeInfo jsonTypeInfo) { }
         [System.Diagnostics.CodeAnalysis.RequiresDynamicCodeAttribute("JSON serialization and deserialization might require types that cannot be statically analyzed and might need runtime code generation. Use System.Text.Json source generation for native AOT applications.")]
         [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("JSON serialization and deserialization might require types that cannot be statically analyzed. Use the overload that takes a JsonTypeInfo or JsonSerializerContext, or make sure all of the required types are preserved.")]

src/libraries/System.Text.Json/src/ILLink/ILLink.Substitutions.xml

@@ -1,8 +1,8 @@
 <linker>
   <assembly fullname="System.Text.Json">
-    <type fullname="System.Text.Json.AppContextSwitchHelper">
-      <method signature="System.Boolean get_UseReflectionDefault()" body="stub" value="false" 
-              feature="System.Text.Json.Serialization.UseReflectionDefault" featurevalue="false"/>
+    <type fullname="System.Text.Json.JsonSerializer">
+      <method signature="System.Boolean get_IsReflectionEnabledByDefault()" body="stub" value="false" 
+              feature="System.Text.Json.JsonSerializer.IsReflectionEnabledByDefault" featurevalue="false"/>
     </type>
   </assembly>
 </linker>

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

@@ -5,12 +5,6 @@ namespace System.Text.Json
 {
     internal static class AppContextSwitchHelper
     {
-        public static bool UseReflectionDefault { get; } =
-            AppContext.TryGetSwitch(
-                switchName: "System.Text.Json.Serialization.UseReflectionDefault",
-                isEnabled: out bool value)
-            ? value : true;
-
         public static bool IsSourceGenReflectionFallbackEnabled { get; } =
             AppContext.TryGetSwitch(
                 switchName: "System.Text.Json.Serialization.EnableSourceGenReflectionFallback",

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Helpers.cs

@@ -13,6 +13,21 @@ public static partial class JsonSerializer
         internal const string SerializationUnreferencedCodeMessage = "JSON serialization and deserialization might require types that cannot be statically analyzed. Use the overload that takes a JsonTypeInfo or JsonSerializerContext, or make sure all of the required types are preserved.";
         internal const string SerializationRequiresDynamicCodeMessage = "JSON serialization and deserialization might require types that cannot be statically analyzed and might need runtime code generation. Use System.Text.Json source generation for native AOT applications.";
 
+        /// <summary>
+        /// Indicates whether unconfigured <see cref="JsonSerializerOptions"/> instances
+        /// should be set to use the reflection-based <see cref="DefaultJsonTypeInfoResolver"/>.
+        /// </summary>
+        /// <remarks>
+        /// The value of the property is backed by the "System.Text.Json.JsonSerializer.IsReflectionEnabledByDefault"
+        /// feature switch and defaults to <see langword="true"/> if unset. For trimmed applications, disabling the feature switch
+        /// at link time will result in the property being substituted with a constant <see langword="false"/> value.
+        /// </remarks>
+        public static bool IsReflectionEnabledByDefault { get; } =
+            AppContext.TryGetSwitch(
+                switchName: "System.Text.Json.JsonSerializer.IsReflectionEnabledByDefault",
+                isEnabled: out bool value)
+            ? value : true;
+
         [RequiresUnreferencedCode(SerializationUnreferencedCodeMessage)]
         [RequiresDynamicCode(SerializationRequiresDynamicCodeMessage)]
         private static JsonTypeInfo GetTypeInfo(JsonSerializerOptions? options, Type inputType, bool fallBackToNearestAncestorType = false)

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.Converters.cs

@@ -45,7 +45,7 @@ public JsonConverter GetConverter(Type typeToConvert)
                 ThrowHelper.ThrowArgumentNullException(nameof(typeToConvert));
             }
 
-            if (AppContextSwitchHelper.UseReflectionDefault && _typeInfoResolver is null)
+            if (JsonSerializer.IsReflectionEnabledByDefault && _typeInfoResolver is null)
             {
                 // Backward compatibility -- root & query the default reflection converters
                 // but do not populate the TypeInfoResolver setting.

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.cs

@@ -680,7 +680,7 @@ public void MakeReadOnly()
         [RequiresDynamicCode(JsonSerializer.SerializationRequiresDynamicCodeMessage)]
         internal void ConfigureForJsonSerializer()
         {
-            if (AppContextSwitchHelper.UseReflectionDefault)
+            if (JsonSerializer.IsReflectionEnabledByDefault)
             {
                 // Even if a resolver has already been specified, we need to root
                 // the default resolver to gain access to the default converters.
@@ -834,7 +834,7 @@ private static JsonSerializerOptions GetOrCreateDefaultOptionsInstance()
                 // we need to specify a resolver instance for the case where
                 // reflection is disabled by default: use one that returns null for all types.
 
-                TypeInfoResolver = AppContextSwitchHelper.UseReflectionDefault
+                TypeInfoResolver = JsonSerializer.IsReflectionEnabledByDefault
                     ? DefaultJsonTypeInfoResolver.RootDefaultInstance()
                     : new JsonTypeInfoResolverChain(),
 

src/libraries/System.Text.Json/tests/System.Text.Json.Tests/Serialization/OptionsTests.cs

@@ -481,20 +481,28 @@ public static void Options_JsonSerializerContext_DoesNotFallbackToReflection()
             Assert.Throws<NotSupportedException>(() => JsonSerializer.Serialize(unsupportedValue, options));
         }
 
+        [Fact]
+        public static void JsonSerializer_IsReflectionEnabledByDefault_DefaultsToTrue()
+        {
+            Assert.True(JsonSerializer.IsReflectionEnabledByDefault);
+        }
+
         [SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework)]
         [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
-        public static void Options_DisablingUseReflectionDefaultSwitch_DefaultOptionsDoesNotSupportReflection()
+        public static void Options_DisablingIsReflectionEnabledByDefaultSwitch_DefaultOptionsDoesNotSupportReflection()
         {
             var options = new RemoteInvokeOptions
             {
                 RuntimeConfigurationOptions =
                 {
-                    ["System.Text.Json.Serialization.UseReflectionDefault"] = false
+                    ["System.Text.Json.JsonSerializer.IsReflectionEnabledByDefault"] = false
                 }
             };
 
             RemoteExecutor.Invoke(static () =>
             {
+                Assert.False(JsonSerializer.IsReflectionEnabledByDefault);
+
                 var options = JsonSerializerOptions.Default;
                 Assert.True(options.IsReadOnly);
 
@@ -519,18 +527,20 @@ public static void Options_DisablingUseReflectionDefaultSwitch_DefaultOptionsDoe
 
         [SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework)]
         [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
-        public static void Options_DisablingUseReflectionDefaultSwitch_NewOptionsDoesNotSupportReflection()
+        public static void Options_DisablingIsReflectionEnabledByDefaultSwitch_NewOptionsDoesNotSupportReflection()
         {
             var options = new RemoteInvokeOptions
             {
                 RuntimeConfigurationOptions =
                 {
-                    ["System.Text.Json.Serialization.UseReflectionDefault"] = false
+                    ["System.Text.Json.JsonSerializer.IsReflectionEnabledByDefault"] = false
                 }
             };
 
             RemoteExecutor.Invoke(static () =>
             {
+                Assert.False(JsonSerializer.IsReflectionEnabledByDefault);
+
                 var options = new JsonSerializerOptions();
                 Assert.False(options.IsReadOnly);
 
@@ -561,18 +571,20 @@ public static void Options_DisablingUseReflectionDefaultSwitch_NewOptionsDoesNot
 
         [SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework)]
         [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
-        public static void Options_DisablingUseReflectionDefaultSwitch_CanUseSourceGen()
+        public static void Options_DisablingIsReflectionEnabledByDefaultSwitch_CanUseSourceGen()
         {
             var options = new RemoteInvokeOptions
             {
                 RuntimeConfigurationOptions =
                 {
-                    ["System.Text.Json.Serialization.UseReflectionDefault"] = false
+                    ["System.Text.Json.JsonSerializer.IsReflectionEnabledByDefault"] = false
                 }
             };
 
             RemoteExecutor.Invoke(static () =>
             {
+                Assert.False(JsonSerializer.IsReflectionEnabledByDefault);
+
                 var options = new JsonSerializerOptions();
                 options.TypeInfoResolverChain.Add(JsonContext.Default);
 
@@ -654,19 +666,21 @@ public static void Options_JsonSerializerContext_Net6CompatibilitySwitch_FallsBa
 
         [SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework)]
         [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
-        public static void Options_JsonSerializerContext_Net6CompatibilitySwitch_IsOverriddenByDisablingUseReflectionDefault()
+        public static void Options_JsonSerializerContext_Net6CompatibilitySwitch_IsOverriddenByDisablingIsReflectionEnabledByDefault()
         {
             var options = new RemoteInvokeOptions
             {
                 RuntimeConfigurationOptions =
                 {
-                    ["System.Text.Json.Serialization.UseReflectionDefault"] = false,
+                    ["System.Text.Json.JsonSerializer.IsReflectionEnabledByDefault"] = false,
                     ["System.Text.Json.Serialization.EnableSourceGenReflectionFallback"] = true
                 }
             };
 
             RemoteExecutor.Invoke(static () =>
             {
+                Assert.False(JsonSerializer.IsReflectionEnabledByDefault);
+
                 JsonContext context = JsonContext.Default;
                 var unsupportedValue = new MyClass();
 

src/libraries/System.Text.Json/tests/System.Text.Json.Tests/System.Text.Json.Tests.csproj

@@ -264,6 +264,9 @@
   <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETFramework'">
     <Compile Include="$(CommonPath)System\Buffers\ArrayBufferWriter.cs" Link="CommonTest\System\Buffers\ArrayBufferWriter.cs" />
   </ItemGroup>
+  <ItemGroup>
+    <None Include="TrimmingTests\IsReflectionEnabledByDefaultFalse.cs" />
+  </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="$(LibrariesProjectRoot)System.IO.Pipelines\src\System.IO.Pipelines.csproj" />
   </ItemGroup>

src/libraries/System.Text.Json/tests/System.Text.Json.Tests/TrimmingTests/UseReflectionDefaultFalse.cs → src/libraries/System.Text.Json/tests/System.Text.Json.Tests/TrimmingTests/IsReflectionEnabledByDefaultFalse.cs

@@ -12,7 +12,7 @@
 public static class Program
 {
     // Validates that expected the components are trimmed when
-    // the UseReflectionDefault feature switch is turned on.
+    // the IsReflectionEnabledByDefault feature switch is turned on.
     public static int Main()
     {
         MyPoco valueToSerialize = new MyPoco { Value = 42 };

src/libraries/System.Text.Json/tests/System.Text.Json.Tests/TrimmingTests/System.Text.Json.TrimmingTests.proj

@@ -60,8 +60,8 @@
     <TestConsoleAppSourceFiles Include="EnumConverterTest.cs" />
     <TestConsoleAppSourceFiles Include="JsonConverterAttributeTest.cs" />
     <TestConsoleAppSourceFiles Include="StackOrQueueNotRootedTest.cs" />
-    <TestConsoleAppSourceFiles Include="UseReflectionDefaultFalse.cs">
-      <DisabledFeatureSwitches>System.Text.Json.Serialization.UseReflectionDefault</DisabledFeatureSwitches>
+    <TestConsoleAppSourceFiles Include="IsReflectionEnabledByDefaultFalse.cs">
+      <DisabledFeatureSwitches>System.Text.Json.JsonSerializer.IsReflectionEnabledByDefault</DisabledFeatureSwitches>
     </TestConsoleAppSourceFiles>
   </ItemGroup>