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Fatal error: exception Ctype.Unify(_) #6513

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vicuna opened this issue Aug 12, 2014 · 3 comments

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commented Aug 12, 2014

Original bug ID: 6513
Reporter: dario
Assigned to: @garrigue
Status: closed (set by @xavierleroy on 2017-02-16T14:16:28Z)
Resolution: fixed
Priority: high
Severity: major
Version: 4.02.0+beta1 / +rc1
Target version: 4.02.1+dev
Fixed in version: 4.02.0+dev
Category: typing
Related to: #6981

Bug description

The following mli code causes the compiler to abort with a Ctype.Unify(_)
exception. This happens both in 4.01.0 and the latest 4.02 trunk snapshot
(both installed via OPAM).

To attempt compilation you need the latest Tyxml installed. Running
"ocamlfind ocamlc -package tyxml -c test.mli" suffices to reproduce
the error. (My apologies for not being able to produce a self-contained
example. I found that even small tweaks to the functor make the problem
go away.)

module type S =
sig
type t
type u
end

module Make: functor (Html5: Html5_sigs.T with type 'a Xml.wrap = 'a and type 'a wrap = 'a and type 'a list_wrap = 'a list) -> S with
type t = Html5_types.div Html5.elt and
type u = < foo: Html5.uri >

Steps to reproduce

  1. Install Tyxml 3.2.x (e.g. "opam install tyxml")

  2. Save code fragment as test.mli

  3. ocamlfind ocamlc -package tyxml -c test.mli

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commented Aug 20, 2014

Comment author: @mshinwell

Jacques, do you have any time to have a look at this one?

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commented Aug 21, 2014

Comment author: @garrigue

I'm back from holidays today and I'll try to look into it,
but the opam dependency makes things harder.

@vicuna

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commented Aug 21, 2014

Comment author: @garrigue

Fixed in 4.02, at revision 15119.

The problem was a missing Ctype.init_def(Ident.current_time())
after introducing the functor argument in the environment.
As a result, update_level would fail attempting to lower the
level of the argument below its stamp.

The following stripped down example has no dependencies:

module type S = sig type u end

module type T = sig
type 'a wrap
type uri
end

module Make: functor (Html5 : T with type 'a wrap = 'a) ->
S with type u = < foo : Html5.uri >

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