Comment author: dsheets

Ugh. Those links should be mirage/ocaml-cohttp@c429f5e#diff-19a3a7db54ab863fd07186df30450b0eR37 and https://travis-ci.org/mirage/ocaml-cohttp/jobs/57781176#L3082 because '>' is not a valid URI character and is traditionally used to indicate the end of a URI.

Comment author: dsheets

The following crashes utop (but not the toplevel) with the same exception:

module M = struct type 'a t = 'a let return a = a end

module F(M : sig
type 'a t
val return : 'a -> 'a t
end) : sig
val q : unit -> [ Ok ] M.t end = struct let q () = M.return Ok
end

module A = F(M)
;;

A.q ();;

Comment author: dsheets

This issue was reported as a utop issue about 1 year ago by nojb: ocaml-community/utop#60

Comment author: @yallop

You can crash the toplevel or ocamlc if you pass -short-paths:

$ cat bug.ml
module M = struct type 'a t = 'a end

module F(M : sig type 'a t end) : sig
val q : unit -> [ `Ok ] M.t
end = struct
let q () = assert false
end

module A = F(M)

let f () = A.q ()
$ ocamlc -i -short-paths bug.ml
Fatal error: exception File "typing/printtyp.ml", line 583, characters 12-18: Assertion failed

Comment author: dsheets

In my initial case, removing -short-paths avoids the assertion error and there is no masked type error. In this case, using -short-paths prevents an otherwise correct ml file from being built into a cmo.

Comment author: @damiendoligez

For future reference, I needed the following commands to trigger the repro case:

git clone https://github.com/dsheets/ocaml-cohttp.git
cd ocaml-cohttp
git checkout c429f5ea47b2792a4c3e2136a6ca8c3557031c9c
opam install cohttp.0.15.2 --deps-only
opam install magic-mime
ocaml setup.ml -configure --enable-tests
make test

Comment author: @yallop

In my initial case, removing -short-paths avoids the assertion error and there is no masked type error. In this case, using -short-paths prevents an otherwise correct ml file from being built into a cmo.

I'm not sure I understand the distinction (if there is a distinction). It appears that in both cases using -short-paths triggers an assertion error, aborting the compilation of a correct program.

Comment author: dsheets

There is no grand distinction. In your example bug.ml, without -i, the cmo builds fine. I was just wanting to make clear that the assertion error can occur even when type printing is not obviously involved. In that case (the original), an otherwise correct program is not built.

Comment author: @yallop

Ah, I see. Either -i or -annot will trigger the problem, I think.

Comment author: @garrigue

Wrong assumption...

Fixed in trunk and 4.02 at revisions 16013 and 16014.

Note that outcometree is actually incorrect: it requires the row name to be a constructor, but the parser allows any type expression. Fixing this would simplify the code.