Original bug ID: 7937
Reporter: georges.duperon
Assigned to: @Octachron
Status: resolved (set by @Octachron on 2019-03-07T11:09:56Z)
Resolution: fixed
Priority: normal
Severity: crash
Platform: Linux
OS: Debian
OS Version: Debian 9
Version: 4.07.0
Fixed in version: 4.09.0+dev
Category: typing
Monitored by: @nojb @gasche

Bug description

Fatal error: exception Ctype.Unify(_)

Triggered by this minimized version (credits go to Paul Laforgue):

type 'a fb = 'a constraint 'a = [< `K of int & 'a];;
let g : 'a. 'a fb -> bool = fun v -> v = true;;

More verbose version:

type ('a, 'select) fb = 'a constraint 'select = [< L of int & 'a | R of bool & 'a ];;
let g : 'a 'select . ('a, 'select) fb -> bool = fun v -> v = true;;

Steps to reproduce

$ cat oops.ml
type 'a fb = 'a constraint 'a = [< `K of int & 'a];;
let g : 'a. 'a fb -> bool = fun v -> v = true;;
$ ocamlc -i oops.ml
Fatal error: exception Ctype.Unify(_)