Fix JsonException message property type info in class parameterized constructor

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

@@ -540,7 +540,9 @@ public static void AddJsonExceptionInformation(scoped ref ReadStack state, in Ut
             if (string.IsNullOrEmpty(message))
             {
                 // Use a default message.
-                Type propertyType = state.Current.JsonPropertyInfo?.PropertyType ?? state.Current.JsonTypeInfo.Type;
+                Type propertyType = state.Current.JsonPropertyInfo?.PropertyType ??
+                    state.Current.CtorArgumentState?.JsonParameterInfo?.ParameterType ??
+                    state.Current.JsonTypeInfo.Type;
                 message = SR.Format(SR.DeserializeUnableToConvertValue, propertyType);
                 ex.AppendPathInformation = true;
             }

src/libraries/System.Text.Json/tests/Common/ConstructorTests/ConstructorTests.Exceptions.cs

@@ -350,5 +350,31 @@ public ClassWithInvalidDictionary(Dictionary<string, int[,]> unsupportedDictiona
                 UnsupportedDictionary = unsupportedDictionary;
             }
         }
+
+        [Fact]
+        public async Task ParameterizedConstructor_ExceptionMessage_ReportsPropertyType()
+        {
+            // Regression test: classes with parameterized constructors should report the
+            // property type (System.String), not the declaring class type, in the JsonException message.
+            // https://github.com/dotnet/runtime/pull/126575
+            JsonException e;
+
+            e = await Assert.ThrowsAsync<JsonException>(() =>
+                Serializer.DeserializeWrapper<ParameterizedClass_WithStringProperty>("""{"Text":{}}"""));
+            Assert.Contains("System.String", e.Message);
+            Assert.DoesNotContain(nameof(ParameterizedClass_WithStringProperty), e.Message);
+
+            e = await Assert.ThrowsAsync<JsonException>(() =>
+                Serializer.DeserializeWrapper<ParameterizedRecord_WithStringProperty>("""{"Text":{}}"""));
+            Assert.Contains("System.String", e.Message);
+            Assert.DoesNotContain(nameof(ParameterizedRecord_WithStringProperty), e.Message);
+        }
+
+        public class ParameterizedClass_WithStringProperty(string text)
+        {
+            public string Text { get; set; } = text;
+        }
+
+        public record ParameterizedRecord_WithStringProperty(string Text);
     }
 }

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Tests/Serialization/ConstructorTests.cs

@@ -177,6 +177,8 @@ protected ConstructorTests_Metadata(JsonSerializerWrapper stringWrapper)
         [JsonSerializable(typeof(TypeWith_RefReadonlyParameter_Primitive))]
         [JsonSerializable(typeof(TypeWith_RefReadonlyParameter_Struct))]
         [JsonSerializable(typeof(TypeWith_RefReadonlyParameter_ReferenceType))]
+        [JsonSerializable(typeof(ParameterizedClass_WithStringProperty))]
+        [JsonSerializable(typeof(ParameterizedRecord_WithStringProperty))]
         internal sealed partial class ConstructorTestsContext_Metadata : JsonSerializerContext
         {
         }
@@ -349,6 +351,8 @@ public ConstructorTests_Default(JsonSerializerWrapper jsonSerializer) : base(jso
         [JsonSerializable(typeof(TypeWith_RefReadonlyParameter_Primitive))]
         [JsonSerializable(typeof(TypeWith_RefReadonlyParameter_Struct))]
         [JsonSerializable(typeof(TypeWith_RefReadonlyParameter_ReferenceType))]
+        [JsonSerializable(typeof(ParameterizedClass_WithStringProperty))]
+        [JsonSerializable(typeof(ParameterizedRecord_WithStringProperty))]
         internal sealed partial class ConstructorTestsContext_Default : JsonSerializerContext
         {
         }