Non-recursive GADT gets a different error depending on which constructor is a GADT #9067

A GADT constructor in a type declared without rec is reported in two different ways.

When the first constructor is a GADT constructor:

type t<'a> = A(int): t<int>

GADTs require recursive type syntax.
Define your type using `type rec` instead of `type`.
Example: type rec t = ...

When a later constructor is one, or in a signature:

type t<_> = Plain | Indexed(int): t<int>

GADT case syntax cannot be used in a 'nonrec' block.

nonrec is not ReScript syntax. The first message comes from a check in bs_ast_invariant.ml that only looks at the first constructor of a structure item; the second is the type checker's own error (Nonrec_gadt in typedecl.ml), which covers every case. The first message also isn't indented like the rest of the error.