Why does `SchemaMappingInspector ` doesn't check type mismatches ?

[aynesh]

A quick question, why doesn't SchemaMappingInspector doesn't validate if for eg:

Type Query {
      helloWord: String
}

and implementation returns an Int

@Controller
class TestGraphqlController {

    @QueryMapping
    fun helloWord: Int {
        return 123
    }
}

In this case, there is a type mismatch. Although this fails at runtime, earlier detection is better. Is it intentional that users can implement their own Coercing? or any other reason! Thank you.

[bclozel]

Hey @aynesh

Indeed, the main goal of the schema inspector is to provide hints and to avoid false positives as much as possible. Having false positives during startup can be really problematic as developers might choose to register a different schema inspection handler that fails hard when errors are reported.

As far as I'm aware, there is no static way to check whether a particular type can be coerced to another one. Coercing implementations can even be Coercing<Object, Object>. The only definitive way to check whether coercing can work is to call serialize or parseValue with actual values.

Maybe we can use heuristics that are somewhat safe and would cause very little false positives. I'll discuss that with the team.