Add GetTypeInfo<T>() and TryGetTypeInfo<T>() to JsonSerializerOptions

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

@@ -457,11 +457,13 @@ public JsonSerializerOptions(System.Text.Json.JsonSerializerOptions options) { }
         [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Getting a converter for a type may require reflection which depends on unreferenced code.")]
         public System.Text.Json.Serialization.JsonConverter GetConverter(System.Type typeToConvert) { throw null; }
         public System.Text.Json.Serialization.Metadata.JsonTypeInfo GetTypeInfo(System.Type type) { throw null; }
+        public System.Text.Json.Serialization.Metadata.JsonTypeInfo<T> GetTypeInfo<T>() { throw null; }
         public void MakeReadOnly() { }
         [System.Diagnostics.CodeAnalysis.RequiresDynamicCodeAttribute("Populating unconfigured TypeInfoResolver properties with the reflection resolver requires runtime code generation.")]
         [System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute("Populating unconfigured TypeInfoResolver properties with the reflection resolver requires unreferenced code.")]
         public void MakeReadOnly(bool populateMissingResolver) { }
         public bool TryGetTypeInfo(System.Type type, [System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] out System.Text.Json.Serialization.Metadata.JsonTypeInfo? typeInfo) { throw null; }
+        public bool TryGetTypeInfo<T>([System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] out System.Text.Json.Serialization.Metadata.JsonTypeInfo<T>? typeInfo) { throw null; }
     }
     public enum JsonTokenType : byte
     {

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

@@ -90,6 +90,37 @@ public bool TryGetTypeInfo(Type type, [NotNullWhen(true)] out JsonTypeInfo? type
             return typeInfo is not null;
         }
 
+        /// <summary>
+        /// Gets the <see cref="JsonTypeInfo{T}"/> contract metadata resolved by the current <see cref="JsonSerializerOptions"/> instance.
+        /// </summary>
+        /// <typeparam name="T">The type to resolve contract metadata for.</typeparam>
+        /// <returns>The contract metadata resolved for <typeparamref name="T"/>.</returns>
+        /// <exception cref="ArgumentException"><typeparamref name="T"/> is not valid for serialization.</exception>
+        /// <remarks>
+        /// If the <see cref="JsonSerializerOptions"/> instance is locked for modification, the method will return a cached instance for the metadata.
+        /// </remarks>
+        public JsonTypeInfo<T> GetTypeInfo<T>()
+        {
+            return (JsonTypeInfo<T>)GetTypeInfo(typeof(T));
+        }
+
+        /// <summary>
+        /// Tries to get the <see cref="JsonTypeInfo{T}"/> contract metadata resolved by the current <see cref="JsonSerializerOptions"/> instance.
+        /// </summary>
+        /// <typeparam name="T">The type to resolve contract metadata for.</typeparam>
+        /// <param name="typeInfo">The resolved contract metadata, or <see langword="null" /> if no contract could be resolved.</param>
+        /// <returns><see langword="true"/> if a contract for <typeparamref name="T"/> was found, or <see langword="false"/> otherwise.</returns>
+        /// <exception cref="ArgumentException"><typeparamref name="T"/> is not valid for serialization.</exception>
+        /// <remarks>
+        /// If the <see cref="JsonSerializerOptions"/> instance is locked for modification, the method will return a cached instance for the metadata.
+        /// </remarks>
+        public bool TryGetTypeInfo<T>([NotNullWhen(true)] out JsonTypeInfo<T>? typeInfo)
+        {
+            bool success = TryGetTypeInfo(typeof(T), out JsonTypeInfo? nonGeneric);
+            typeInfo = (JsonTypeInfo<T>?)nonGeneric;
+            return success;
+        }
+
         /// <summary>
         /// Same as GetTypeInfo but without validation and additional knobs.
         /// </summary>

src/libraries/System.Text.Json/tests/Common/JsonSerializerWrapper.cs

@@ -77,8 +77,12 @@ public virtual JsonTypeInfo GetTypeInfo(Type type, JsonSerializerOptions? option
             return mutable ? options.TypeInfoResolver.GetTypeInfo(type, options) : options.GetTypeInfo(type);
         }
 
-        public JsonTypeInfo<T> GetTypeInfo<T>(JsonSerializerOptions? options = null,bool mutable = false)
-            => (JsonTypeInfo<T>)GetTypeInfo(typeof(T), options, mutable);
+        public JsonTypeInfo<T> GetTypeInfo<T>(JsonSerializerOptions? options = null, bool mutable = false)
+        {
+            options ??= DefaultOptions;
+            options.MakeReadOnly(populateMissingResolver: true);
+            return mutable ? (JsonTypeInfo<T>)options.TypeInfoResolver.GetTypeInfo(typeof(T), options) : options.GetTypeInfo<T>();
+        }
 
         public JsonSerializerOptions GetDefaultOptionsWithMetadataModifier(Action<JsonTypeInfo> modifier)
         {

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

@@ -297,7 +297,7 @@ public static void FastPathSerialization_ResolvingJsonTypeInfo()
         {
             JsonSerializerOptions options = FastPathSerializationContext.Default.Options;
 
-            JsonTypeInfo<JsonMessage> jsonMessageInfo = (JsonTypeInfo<JsonMessage>)options.GetTypeInfo(typeof(JsonMessage));
+            JsonTypeInfo<JsonMessage> jsonMessageInfo = options.GetTypeInfo<JsonMessage>();
             Assert.NotNull(jsonMessageInfo.SerializeHandler);
 
             var value = new JsonMessage { Message = "Hi" };
@@ -325,7 +325,7 @@ public static void FastPathSerialization_AppendedResolver_WorksAsExpected(IJsonT
                 TypeInfoResolver = JsonTypeInfoResolver.Combine(fastPathContext, appendedResolver, new DefaultJsonTypeInfoResolver())
             };
 
-            JsonTypeInfo<PocoWithInteger> jsonMessageInfo = (JsonTypeInfo<PocoWithInteger>)options.GetTypeInfo(typeof(PocoWithInteger));
+            JsonTypeInfo<PocoWithInteger> jsonMessageInfo = options.GetTypeInfo<PocoWithInteger>();
             Assert.NotNull(jsonMessageInfo.SerializeHandler);
 
             var value = new PocoWithInteger { Value = 42 };
@@ -339,7 +339,7 @@ public static void FastPathSerialization_AppendedResolver_WorksAsExpected(IJsonT
             Assert.Equal(expectedJson, json);
             Assert.Equal(2, fastPathContext.FastPathInvocationCount);
 
-            JsonTypeInfo<ContainingClass> classInfo = (JsonTypeInfo<ContainingClass>)options.GetTypeInfo(typeof(ContainingClass));
+            JsonTypeInfo<ContainingClass> classInfo = options.GetTypeInfo<ContainingClass>();
             Assert.Null(classInfo.SerializeHandler);
 
             var largerValue = new ContainingClass { Message = value };
@@ -367,7 +367,7 @@ public static void FastPathSerialization_PrependedResolver_CompatibleResolvers_W
                 TypeInfoResolver = JsonTypeInfoResolver.Combine(prependedResolver, fastPathContext, new DefaultJsonTypeInfoResolver())
             };
 
-            JsonTypeInfo<PocoWithInteger> jsonMessageInfo = (JsonTypeInfo<PocoWithInteger>)options.GetTypeInfo(typeof(PocoWithInteger));
+            JsonTypeInfo<PocoWithInteger> jsonMessageInfo = options.GetTypeInfo<PocoWithInteger>();
             Assert.NotNull(jsonMessageInfo.SerializeHandler);
 
             var value = new PocoWithInteger { Value = 42 };
@@ -381,7 +381,7 @@ public static void FastPathSerialization_PrependedResolver_CompatibleResolvers_W
             Assert.Equal(expectedJson, json);
             Assert.Equal(2, fastPathContext.FastPathInvocationCount);
 
-            JsonTypeInfo<ContainingClass> classInfo = (JsonTypeInfo<ContainingClass>)options.GetTypeInfo(typeof(ContainingClass));
+            JsonTypeInfo<ContainingClass> classInfo = options.GetTypeInfo<ContainingClass>();
             Assert.Null(classInfo.SerializeHandler);
 
             var largerValue = new ContainingClass { Message = value };
@@ -409,7 +409,7 @@ public static void FastPathSerialization_PrependedResolver_IncompatibleResolvers
                 TypeInfoResolver = JsonTypeInfoResolver.Combine(prependedResolver, fastPathContext, new DefaultJsonTypeInfoResolver())
             };
 
-            JsonTypeInfo<PocoWithInteger> jsonMessageInfo = (JsonTypeInfo<PocoWithInteger>)options.GetTypeInfo(typeof(PocoWithInteger));
+            JsonTypeInfo<PocoWithInteger> jsonMessageInfo = options.GetTypeInfo<PocoWithInteger>();
             Assert.NotNull(jsonMessageInfo.SerializeHandler);
 
             var value = new PocoWithInteger { Value = 42 };
@@ -423,7 +423,7 @@ public static void FastPathSerialization_PrependedResolver_IncompatibleResolvers
             Assert.Equal(expectedJson, json);
             Assert.Equal(0, fastPathContext.FastPathInvocationCount);
 
-            JsonTypeInfo<ContainingClass> classInfo = (JsonTypeInfo<ContainingClass>)options.GetTypeInfo(typeof(ContainingClass));
+            JsonTypeInfo<ContainingClass> classInfo = options.GetTypeInfo<ContainingClass>();
             Assert.Null(classInfo.SerializeHandler);
 
             var largerValue = new ContainingClass { Message = value };
@@ -564,7 +564,7 @@ public static void ChainedContexts_Serialization<T>(T value, string expectedJson
         {
             var options = new JsonSerializerOptions { TypeInfoResolverChain = { NestedContext.Default, PersonJsonContext.Default } };
 
-            JsonTypeInfo<T> typeInfo = (JsonTypeInfo<T>)options.GetTypeInfo(typeof(T))!;
+            JsonTypeInfo<T> typeInfo = options.GetTypeInfo<T>();
 
             string json = JsonSerializer.Serialize(value, typeInfo);
             JsonTestHelper.AssertJsonEqual(expectedJson, json);
@@ -822,7 +822,7 @@ public TestResolver(Func<Type, JsonSerializerOptions, JsonTypeInfo?> getTypeInfo
         public static void FastPathSerialization_EvaluatePropertyOnlyOnceWhenIgnoreNullOrDefaultIsSpecified()
         {
             JsonSerializerOptions options = FastPathSerializationContext.Default.Options;
-            JsonTypeInfo<AllocatingOnPropertyAccess> allocatingOnPropertyAccessInfo = (JsonTypeInfo<AllocatingOnPropertyAccess>)options.GetTypeInfo(typeof(AllocatingOnPropertyAccess));
+            JsonTypeInfo<AllocatingOnPropertyAccess> allocatingOnPropertyAccessInfo = options.GetTypeInfo<AllocatingOnPropertyAccess>();
             Assert.NotNull(allocatingOnPropertyAccessInfo.SerializeHandler);
 
             var value = new AllocatingOnPropertyAccess();

src/libraries/System.Text.Json/tests/System.Text.Json.Tests/JsonNode/JsonValueTests.cs

@@ -610,7 +610,7 @@ public static void GetValueKind()
         public static void GetValueKind_NumberHandling(JsonNumberHandling numberHandling, JsonValueKind expectedKind)
         {
             JsonSerializerOptions options = new(JsonSerializerOptions.Default) { NumberHandling = numberHandling };
-            JsonTypeInfo<int> typeInfo = (JsonTypeInfo<int>)options.GetTypeInfo(typeof(int));
+            JsonTypeInfo<int> typeInfo = options.GetTypeInfo<int>();
             JsonValue value = JsonValue.Create(42, typeInfo);
             Assert.Equal(expectedKind, value.GetValueKind());
         }

src/libraries/System.Text.Json/tests/System.Text.Json.Tests/Serialization/CustomConverterTests/CustomConverterTests.Object.cs

@@ -778,7 +778,7 @@ void TestValue<T>(T value, string expectedJson)
                 string json = JsonSerializer.Serialize(value, options);
                 Assert.Equal(expectedJson, json);
 
-                JsonTypeInfo<T> jsonTypeInfo = (JsonTypeInfo<T>)options.GetTypeInfo(typeof(T));
+                JsonTypeInfo<T> jsonTypeInfo = options.GetTypeInfo<T>();
                 json = JsonSerializer.Serialize(value, jsonTypeInfo);
                 Assert.Equal(expectedJson, json);
             }

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

@@ -1809,7 +1809,7 @@ public static void GetTypeInfo_ImmutableOptionsInstance(Type type)
         public static void GetTypeInfo_MutableOptions_CanModifyMetadata()
         {
             var options = new JsonSerializerOptions { TypeInfoResolver = new DefaultJsonTypeInfoResolver() };
-            JsonTypeInfo<TestClassForEncoding> jti = (JsonTypeInfo<TestClassForEncoding>)options.GetTypeInfo(typeof(TestClassForEncoding));
+            JsonTypeInfo<TestClassForEncoding> jti = options.GetTypeInfo<TestClassForEncoding>();
 
             Assert.False(jti.IsReadOnly);
             Assert.Equal(1, jti.Properties.Count);
@@ -1827,14 +1827,14 @@ public static void GetTypeInfo_MutableOptions_CanModifyMetadata()
             Assert.Throws<InvalidOperationException>(() => options.IncludeFields = false);
 
             // Getting JsonTypeInfo now should return a fresh immutable instance
-            JsonTypeInfo<TestClassForEncoding> jti2 = (JsonTypeInfo<TestClassForEncoding>)options.GetTypeInfo(typeof(TestClassForEncoding));
+            JsonTypeInfo<TestClassForEncoding> jti2 = options.GetTypeInfo<TestClassForEncoding>();
             Assert.NotSame(jti, jti2);
             Assert.True(jti2.IsReadOnly);
             Assert.Equal(1, jti2.Properties.Count);
             Assert.Throws<InvalidOperationException>(() => jti2.Properties.Clear());
 
             // Subsequent requests return the same cached value
-            Assert.Same(jti2, options.GetTypeInfo(typeof(TestClassForEncoding)));
+            Assert.Same(jti2, options.GetTypeInfo<TestClassForEncoding>());
 
             // Default contract should produce expected JSON
             json = JsonSerializer.Serialize(value, options);
@@ -1923,7 +1923,7 @@ public static void GetTypeInfo_ResolverWithoutMetadata_ThrowsNotSupportedExcepti
         public static void GetTypeInfo_ResultsAreGeneric<T>(T value, string expectedJson)
         {
             var options = new JsonSerializerOptions { TypeInfoResolver = new DefaultJsonTypeInfoResolver() };
-            JsonTypeInfo<T> jsonTypeInfo = (JsonTypeInfo<T>)options.GetTypeInfo(typeof(T));
+            JsonTypeInfo<T> jsonTypeInfo = options.GetTypeInfo<T>();
             string json = JsonSerializer.Serialize(value, jsonTypeInfo);
             Assert.Equal(expectedJson, json);
             JsonSerializer.Deserialize(json, jsonTypeInfo);
@@ -1940,6 +1940,140 @@ public static IEnumerable<object[]> GetTypeInfo_ResultsAreGeneric_Values()
             static object[] WrapArgs<T>(T value, string json) => new object[] { value, json };
         }
 
+        [Fact]
+        public static void GetTypeInfoGeneric_MutableOptionsInstance()
+        {
+            var options = new JsonSerializerOptions();
+
+            // An unset resolver results in NotSupportedException.
+            Assert.Throws<NotSupportedException>(() => options.GetTypeInfo<int>());
+            Assert.False(options.TryGetTypeInfo<int>(out JsonTypeInfo<int>? typeInfo));
+            Assert.Null(typeInfo);
+
+            options.TypeInfoResolver = new DefaultJsonTypeInfoResolver();
+            JsonTypeInfo<int> typeInfo1 = options.GetTypeInfo<int>();
+            Assert.Equal(typeof(int), typeInfo1.Type);
+            Assert.False(typeInfo1.IsReadOnly);
+
+            JsonTypeInfo<int> typeInfo2 = options.GetTypeInfo<int>();
+            Assert.Equal(typeof(int), typeInfo2.Type);
+            Assert.False(typeInfo2.IsReadOnly);
+
+            Assert.NotSame(typeInfo1, typeInfo2);
+
+            Assert.True(options.TryGetTypeInfo<int>(out JsonTypeInfo<int>? typeInfo3));
+            Assert.Equal(typeof(int), typeInfo3.Type);
+            Assert.False(typeInfo3.IsReadOnly);
+
+            Assert.NotSame(typeInfo1, typeInfo3);
+
+            options.WriteIndented = true; // can mutate without issue
+        }
+
+        [Fact]
+        public static void GetTypeInfoGeneric_ImmutableOptionsInstance()
+        {
+            var options = new JsonSerializerOptions();
+            JsonSerializer.Serialize(42, options);
+
+            JsonTypeInfo<int> typeInfo = options.GetTypeInfo<int>();
+            Assert.Equal(typeof(int), typeInfo.Type);
+            Assert.True(typeInfo.IsReadOnly);
+
+            JsonTypeInfo<int> typeInfo2 = options.GetTypeInfo<int>();
+            Assert.Same(typeInfo, typeInfo2);
+
+            Assert.True(options.TryGetTypeInfo<int>(out JsonTypeInfo<int>? typeInfo3));
+            Assert.Same(typeInfo, typeInfo3);
+        }
+
+        [Fact]
+        public static void GetTypeInfoGeneric_EquivalentToNonGenericVersion()
+        {
+            var options = new JsonSerializerOptions { TypeInfoResolver = new DefaultJsonTypeInfoResolver() };
+            JsonSerializer.Serialize(42, options); // Make options immutable to get caching
+
+            JsonTypeInfo nonGenericTypeInfo = options.GetTypeInfo(typeof(int));
+            JsonTypeInfo<int> genericTypeInfo = options.GetTypeInfo<int>();
+
+            Assert.Same(nonGenericTypeInfo, genericTypeInfo);
+
+            Assert.True(options.TryGetTypeInfo(typeof(string), out JsonTypeInfo? nonGenericTypeInfo2));
+            Assert.True(options.TryGetTypeInfo<string>(out JsonTypeInfo<string>? genericTypeInfo2));
+
+            Assert.Same(nonGenericTypeInfo2, genericTypeInfo2);
+        }
+
+        [Fact]
+        public static void GetTypeInfoGeneric_WorksWithVariousTypes()
+        {
+            var options = new JsonSerializerOptions { TypeInfoResolver = new DefaultJsonTypeInfoResolver() };
+
+            JsonTypeInfo<string> stringTypeInfo = options.GetTypeInfo<string>();
+            Assert.Equal(typeof(string), stringTypeInfo.Type);
+
+            JsonTypeInfo<List<int>> listTypeInfo = options.GetTypeInfo<List<int>>();
+            Assert.Equal(typeof(List<int>), listTypeInfo.Type);
+
+            JsonTypeInfo<Dictionary<string, object>> dictTypeInfo = options.GetTypeInfo<Dictionary<string, object>>();
+            Assert.Equal(typeof(Dictionary<string, object>), dictTypeInfo.Type);
+
+            JsonTypeInfo<object> objectTypeInfo = options.GetTypeInfo<object>();
+            Assert.Equal(typeof(object), objectTypeInfo.Type);
+        }
+
+        [Fact]
+        public static void GetTypeInfoGeneric_ResolverWithoutMetadata_ThrowsNotSupportedException()
+        {
+            var options = new JsonSerializerOptions();
+            options.AddContext<JsonContext>();
+
+            Assert.Throws<NotSupportedException>(() => options.GetTypeInfo<BasicCompany>());
+
+            Assert.False(options.TryGetTypeInfo<BasicCompany>(out JsonTypeInfo<BasicCompany>? typeInfo));
+            Assert.Null(typeInfo);
+        }
+
+        [Fact]
+        public static void GetTypeInfoGeneric_MutableOptions_CanModifyMetadata()
+        {
+            var options = new JsonSerializerOptions { TypeInfoResolver = new DefaultJsonTypeInfoResolver() };
+            JsonTypeInfo<TestClassForEncoding> jti = options.GetTypeInfo<TestClassForEncoding>();
+
+            Assert.False(jti.IsReadOnly);
+            Assert.Equal(1, jti.Properties.Count);
+            jti.Properties.Clear();
+
+            var value = new TestClassForEncoding { MyString = "SomeValue" };
+            Assert.False(options.IsReadOnly);
+
+            string json = JsonSerializer.Serialize(value, jti);
+            Assert.Equal("{}", json);
+
+            // Using JsonTypeInfo will lock JsonSerializerOptions
+            Assert.True(options.IsReadOnly);
+            Assert.True(jti.IsReadOnly);
+            Assert.Throws<InvalidOperationException>(() => options.IncludeFields = false);
+
+            // Getting JsonTypeInfo now should return a fresh immutable instance
+            JsonTypeInfo<TestClassForEncoding> jti2 = options.GetTypeInfo<TestClassForEncoding>();
+            Assert.NotSame(jti, jti2);
+            Assert.True(jti2.IsReadOnly);
+            Assert.Equal(1, jti2.Properties.Count);
+            Assert.Throws<InvalidOperationException>(() => jti2.Properties.Clear());
+
+            // Subsequent requests return the same cached value
+            Assert.Same(jti2, options.GetTypeInfo<TestClassForEncoding>());
+
+            // Default contract should produce expected JSON
+            json = JsonSerializer.Serialize(value, options);
+            Assert.Equal("""{"MyString":"SomeValue"}""", json);
+
+            // Default contract should not impact contract of original JsonTypeInfo
+            json = JsonSerializer.Serialize(value, jti);
+            Assert.Equal("{}", json);
+        }
+
         [Fact]
         public static void AllowDuplicateProperties_RespectsSetting()
         {

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

@@ -86,7 +86,7 @@ public async Task PrimitivesAsRootObject(object? value, string expectedJson)
             Assert.Equal(expectedJson, json);
 
             var options = new JsonSerializerOptions { TypeInfoResolver = new DefaultJsonTypeInfoResolver() };
-            JsonTypeInfo<object> objectTypeInfo = (JsonTypeInfo<object>)options.GetTypeInfo(typeof(object));
+            JsonTypeInfo<object> objectTypeInfo = options.GetTypeInfo<object>();
             json = await Serializer.SerializeWrapper(value, objectTypeInfo);
             Assert.Equal(expectedJson, json);
         }