Fatal error when @deriving(accessors) a Variant with struct payload

[thanglongnamnay]

I get this error when @deriving(accessors) a Variant with struct payload:

Fatal error: exception File "jscomp/frontend/ast_derive_projector.ml", line 57, characters 42-48: Assertion failed

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I don't think the compiler should crash in this situation.

[fhammerschmidt]

@JonoPrest could you have a look?

[JonoPrest]

@JonoPrest could you have a look?

Hey @fhammerschmidt, I saw that assertion when I was fixing some issues on deriving accessors the other day. As far as I can see this has always been the behaviour of the @deriving(accessors).

We can only support support an accessor where the variant parameter is already a defined type. Or we need to generate types for them.

In this example:

@deriving(accessors)
type t = Struct({a: int})

the accessor would need to be:

let struct = (param_0: 'a) => Struct(param_0)

where 'a is unknown unless we generate it.

I think its just better to enforce that it gets defined like this to use accessors:

type structInner = {a: int}

@deriving(accessors)
type t = Struct(structInner)

So maybe the solution is just to improve the error messaging around the failure?

[fhammerschmidt]

You are right, it's just another case of a failed assertion making it to the end user instead of a readable error message. Would you want to improve it?

[JonoPrest]

You are right, it's just another case of a failed assertion making it to the end user instead of a readable error message. Would you want to improve it?

Sure I'll take look and improve the error message during the week 👌🏼