The trait bound... IntoResolvable is not found. ...

[morganmsrn]

Describe the bug

I'm trying to recreate a catch-all Field Result alias type (RequestResult) for mutations and queries, using the methodology advised in the Book by using separate types for Validation errors and Server side errors (converted to Field Errors).
I cannot seem to resolve this message though :

The trait bound std::result::Result<std::result::Result<User, validation::ValidationError>, FieldError>: IntoResolvable<'_, __S, _, database::Database> is not satisfied. The following implementations were found:

• <std::result::Result<(&'a <T as GraphQLValue<S2>>::Context, T), FieldError<S1>> as IntoResolvable<'a, S2, T, C>>
• <std::result::Result<T, E> as IntoResolvable<'a, S, T, C>>
• <std::result::Result<std::option::Option<(&'a <T as GraphQLValue<S2>>::Context, T)>, FieldError<S1>> as IntoResolvable<'a, S2, std::option::Option<T>, C>>

To Reproduce

My code is available right here : https://codeberg.org/morganmsrn/inflow-server
This problem is displayed twice in each of those file : /src/api/sign_in_users.rs and in /src/api/register_user.rs

Here are the alias types and structs that I use :

pub type ServerResult<T> = Result<T, ServerError>;
pub type GraphQLResult<T> = Result<T, ValidationError>;
pub type RequestResult<T> = FieldResult<GraphQLResult<T>>;

The server error is an enum that implements Error (and should convert without a problem to FieldError.
The ValidationError is a struct with a GraphQLObject derive macro, containing a simple "error" String field.

Expected behavior

I would like a solution where the solution mentioned in the book work with a generic result type (User, SessionToken, future objects I have yet to implement)...

[tyranron]

@morganmsrn

I would like a solution where the solution mentioned in the book work with a generic result type

Well that just won't work because of GraphQL type system has no notion of generics. Each concrete GraphQL type should have its own unique name and description, to appear in introspection.

Given a the following generic type:

Result<T, ValidationError>

What name should it have for User? And for SessionToken?

Actually, we may generate by convention like User + ValidationError + Result, so have:

UserValidationErrorResult
SessionTokenValidationErrorResult

we can even strip /Error$/ part by convention, and so have:

UserValidationResult
SessionTokenValidationResult

But what if we want to override a name for some type? Or description?

@LegNeato what do you think? I think auto-implementing GraphQL union for Result<T: GraphQLObject, E: GraphQLObject> will be a huge ergonomics improvement. Actually, in our code base we have a big and fat proc macro machinery for auto-generating such resulty GraphQL unions. Having a convention-driving generic implementation will simplify things a lot. Maybe try it out behind a feature flag first?

[LegNeato]

That sounds like a good idea to try!