assertion failure with type abbreviations

[vicuna]

Original bug ID: 7712
Reporter: mkoconnor
Assigned to: @garrigue
Status: resolved (set by @trefis on 2018-01-23T10:25:57Z)
Resolution: fixed
Priority: normal
Severity: minor
Fixed in version: 4.07.0+dev/beta2/rc1/rc2
Category: typing
Monitored by: @nojb @gasche

Bug description

The following code raises an assertion failure in the compiler for me:

type 'a or_error = string

type ('a, 'b) t_ =
| Bar : ('a, 'a or_error) t_

type 'a t = ('a, 'a) t_

let f : type a. a t -> a t = function
| Bar -> Bar

The first few lines of the stack trace are:

Fatal error: exception File "typing/btype.ml", line 585, characters 6-12: Assertion failed
Raised at file "typing/btype.ml", line 585, characters 6-18
Called from file "typing/btype.ml", line 595, characters 13-40
Called from file "typing/ctype.ml", line 2541, characters 12-34
Called from file "typing/ctype.ml", line 2395, characters 8-32
Re-raised at file "typing/ctype.ml", line 2459, characters 20-188
Called from file "typing/ctype.ml", line 2355, characters 8-24
Re-raised at file "typing/ctype.ml", line 2396, characters 29-51
Called from file "list.ml", line 122, characters 24-31
...

[vicuna]

Comment author: @gasche

I can reproduce with all OCaml versions supporting GADTs, including a reasonably recent trunk.

[vicuna]

Comment author: @trefis

A tentative fix: #1576

[vicuna]

Comment author: @trefis

#1576 was merged.