Unused `ObjectType` referencing custom scalar results in error during schema generation

[SimonCockx]

Current behavior

When I define a custom scalar (e.g., @Scalar('MyCustomScalar')) which I reference in an ObjectType that isn't exposed through any resolver, I run into an error Error: "MyCustomScalar" defined in resolvers, but not in schema during schema generation.

Minimum reproduction code

https://github.com/SimonCockx/nest-gql-scalar-bug

Steps to reproduce

1. Clone https://github.com/SimonCockx/nest-gql-scalar-bug
2. npm install
3. nest start See error.

Expected behavior

I would expect one of these two:

1. @nestjs/graphql successfully determines that the custom scalar is not necessary, so it does not generate it in the schema, but it also doesn't produce an error (which is the case now).
2. @nestjs/graphql just generates the scalar without detecting whether it is referenced in some way. (probably simpler, but I saw the current code already does some reference detection to find only necessary types, so option (1) might be better)

Package version

10.0.16

Graphql version

graphql: 16.5.0 apollo-server-express: 3.9.0

NestJS version

8.0.0

Node.js version

16.15.1

In which operating systems have you tested?

• [ ] macOS
• [X] Windows
• [ ] Linux

[iamkhalidbashir]

Same issue for me It fails on tests but runs fine on dev server

[rickdgeerling]

I can confirm, it still occurs in latest. I've opened a PR with a potential fix.

[kamilmysliwiec]

Let's track this here https://github.com/nestjs/graphql/pull/2428