JsonSerializerOptions.GetTypeInfo throws when TypeInfoResolver is `null`

[brunolins16]

Description

JsonSerializerOptions.TypeInfoResolver is documented as:

A <see langword="null"/> setting is equivalent to using the reflection-based <see cref="[DefaultJsonTypeInfoResolver](https://source.dot.net/System.Text.Json/P/29c640504d3d4bbe.html#29c640504d3d4bbe)" />.
        /// The property will be populated automatically once used with one of the <see cref="[JsonSerializer](https://source.dot.net/System.Text.Json/P/2ca342a99419a245.html#2ca342a99419a245)"/> methods.

This behavior works correctly, however if instead try to obtain the JsonTypeInfo from the JsonSerializerOptions before calling the serializer it fails.

cc @davidfowl @eiriktsarpalis

Reproduction Steps

using System.Text.Json;

var options = new JsonSerializerOptions();
var typeinfo = options.GetTypeInfo(typeof(string));

Expected behavior

When JsonSerializerOptions.TypeInfoResolver is null and a call to JsonSerializerOptions.GetTypeInfo happens it should behave similarly to a call to the JsonSerializer methods.

Probably in AOT-mode DefaultJsonTypeInfoResolver should not need to be set and throws at runtime might be ok.

Actual behavior

System.NotSupportedException
  HResult=0x80131515
  Message=Metadata for type 'System.String' was not provided by TypeInfoResolver of type '<null>'. If using source generation, ensure that all root types passed to the serializer have been indicated with 'JsonSerializableAttribute', along with any types that might be serialized polymorphically.
  Source=System.Text.Json
  StackTrace:
   at System.Text.Json.ThrowHelper.ThrowNotSupportedException_NoMetadataForType(Type type, IJsonTypeInfoResolver resolver) in /_/src/libraries/System.Text.Json/src/System/Text/Json/ThrowHelper.Serialization.cs:line 709
   at System.Text.Json.JsonSerializerOptions.GetTypeInfoInternal(Type type, Boolean ensureConfigured, Boolean resolveIfMutable) in /_/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.Caching.cs:line 75
   at Program.<Main>$(String[] args) in C:\Users\brolivei\source\repos\WebApplication24\Program.cs:line 5

Regression?

No response

Known Workarounds

Manually instantiate the JsonSerializerOptions with the DefaultJsonTypeInfoResolver

eg.:

var options = new JsonSerializerOptions() { TypeInfoResolver = new DefaultJsonTypeInfoResolver() } ;

Configuration

.NET 7

Other information

No response

Tagging subscribers to this area: @dotnet/area-system-text-json, @gregsdennis
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Description

JsonSerializerOptions.TypeInfoResolver is documented as:

A <see langword="null"/> setting is equivalent to using the reflection-based <see cref="[DefaultJsonTypeInfoResolver](https://source.dot.net/System.Text.Json/P/29c640504d3d4bbe.html#29c640504d3d4bbe)" />.
        /// The property will be populated automatically once used with one of the <see cref="[JsonSerializer](https://source.dot.net/System.Text.Json/P/2ca342a99419a245.html#2ca342a99419a245)"/> methods.

This behavior works correctly, however if instead try to obtain the JsonTypeInfo from the JsonSerializerOptions before calling the serializer it fails.

cc @davidfowl @eiriktsarpalis

Reproduction Steps

using System.Text.Json;

var options = new JsonSerializerOptions();
var typeinfo = options.GetTypeInfo(typeof(string));

Expected behavior

When JsonSerializerOptions.TypeInfoResolver is null and a call to JsonSerializerOptions.GetTypeInfo happens it should behave similarly to a call to the JsonSerializer methods.

Probably in AOT-mode DefaultJsonTypeInfoResolver should not need to be set and throws at runtime might be ok.

Actual behavior

System.NotSupportedException
  HResult=0x80131515
  Message=Metadata for type 'System.String' was not provided by TypeInfoResolver of type '<null>'. If using source generation, ensure that all root types passed to the serializer have been indicated with 'JsonSerializableAttribute', along with any types that might be serialized polymorphically.
  Source=System.Text.Json
  StackTrace:
   at System.Text.Json.ThrowHelper.ThrowNotSupportedException_NoMetadataForType(Type type, IJsonTypeInfoResolver resolver) in /_/src/libraries/System.Text.Json/src/System/Text/Json/ThrowHelper.Serialization.cs:line 709
   at System.Text.Json.JsonSerializerOptions.GetTypeInfoInternal(Type type, Boolean ensureConfigured, Boolean resolveIfMutable) in /_/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.Caching.cs:line 75
   at Program.<Main>$(String[] args) in C:\Users\brolivei\source\repos\WebApplication24\Program.cs:line 5

Regression?

No response

Known Workarounds

Manually instantiate the JsonSerializerOptions with the DefaultJsonTypeInfoResolver

eg.:

var options = new JsonSerializerOptions() { TypeInfoResolver = new DefaultJsonTypeInfoResolver() } ;

Configuration

.NET 7

Other information

No response

Author:	brunolins16
Assignees:	-
Labels:	area-System.Text.Json
Milestone:	-

[krwq]

We already have a solution for that in 8.0. Calling options.MakeReadOnly before GetTypeInfo. This has been added here #74431

I think we should leave the issue open for now in case we want to re-iterate on the null in TypeInfoResolver/Combine.
Possibly we could consider adding some flag to control null behavior 🙄

[eiriktsarpalis]

When JsonSerializerOptions.TypeInfoResolver is null and a call to JsonSerializerOptions.GetTypeInfo happens it should behave similarly to a call to the JsonSerializer methods.

The problem with the JsonSerializer methods is that they have to be marked RequiresUnreferencedCode/RequiresDynamicCode precisely because they populate TypeInfoResolver. We decided to go with the throwing behaviour in GetTypeInfo here in order to make it work well with trimming/AOT scenaria.

Probably in AOT-mode DefaultJsonTypeInfoResolver should not need to be set and throws at runtime might be ok.

I don't think we should be conditioning semantics based on the compilation target. A piece of code should work the same way in all targets. This leaves with limited options however, we either need to (carefully) introduce breaking changes or consider new APIs as outlined in #74492. cc @eerhardt

[brunolins16]

The problem with the JsonSerializer methods is that they have to be marked RequiresUnreferencedCode/RequiresDynamicCode precisely because they populate TypeInfoResolver. We decided to go with the throwing behaviour in GetTypeInfo here in order to make it work well with trimming/AOT scenaria.

I got your point, however, in my opinion the JsonSerializerOptions.GetTypeInfo becomes useless when not using a source generator and confusing behavior because I cannot write a simple code, like this:

var options = new JsonSerializerOptions();
var typeinfo = options.GetTypeInfo(typeof(string));
var content = JsonSerializer.Serialize("value", typeinfo);

However, I can write something like this:

var options = new JsonSerializerOptions();
var content = JsonSerializer.Serialize("value", options);

[eiriktsarpalis]

Closing in favor of #83279