Bad (inexistent) error location

[lambdalex-ocp]

Hello,

I'm adding ppx_deriving_yojson into a large project, and sadly at some point, it reports errors at line 1, which we guess is the default location. It makes fixing the errors borderline impossible :(

[gasche]

Sorry about that. Would you have a repro case to test?

[NathanReb]

I'll look into this as I think it's just a matter of generating code with a sensible location. A good place to start would be to make the generated code point to the [@@deriving ...] attribute or the type declaration as is done in other derivers.

I think a typical example of when this bites is something like:

type t = M.t
[@@deriving yojson]

which generates code that relies on M.to_yojson being present. If it's not, the compiler will report the error with the location of the generated code.

I'll add a test case for this as well.