Soundness issue with private rows and module inclusion

[vicuna]

Original bug ID: 7704
Reporter: @yallop
Assigned to: @garrigue
Status: resolved (set by @garrigue on 2018-01-09T07:50:05Z)
Resolution: fixed
Priority: normal
Severity: crash
Fixed in version: 4.06.1+dev/rc1/rc2
Category: typing
Monitored by: igarnier @nojb @gasche

Bug description

With OCaml 4.06.0:

$ cat pr.ml
module M : sig
type t = private [> A of string ] val x : t end = struct type t = private [> A of string | B ] let x = B
end

let _ = match M.x with `A s -> s

$ ocaml pr.ml
Segmentation fault

Additional information

Inspired by PR7703

[vicuna]

Comment author: @lpw25

This seems to have appeared between 4.02.3 and 4.03.0.

[vicuna]

Comment author: @garrigue

Well, to be more precise, matching on an open polymorphic variant type without a default case should raise a warning, so this is not directly related to modules.

Here is a smaller example.

type t = private [> A of string ];; function (A x : t) -> x;;

This might be related to the refinement of Parmatch for GADTs, but it's not immediate why, I will look into it.

[vicuna]

Comment author: @garrigue

Fix in #1559: #1559

Someone review please...

[vicuna]

Comment author: @yallop

this is not directly related to modules

Oops -- indeed. Thanks for the diagnosis & fix.

[vicuna]

Comment author: @garrigue

Fixed in trunk and 4.06 branch by commits bd1b5a0 and 9d52b4c.

[vicuna]

Comment author: @garrigue

Open a new PR (#1564) to provide better naming for the tags.