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Stack overflow with private row type #4580

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vicuna opened this Issue Jul 17, 2008 · 3 comments

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commented Jul 17, 2008

Original bug ID: 4580
Reporter: @yallop
Assigned to: @garrigue
Status: closed (set by @garrigue on 2010-04-27T07:17:15Z)
Resolution: fixed
Priority: normal
Severity: major
Version: 3.10.2
Fixed in version: 3.11+dev
Category: ~DO NOT USE (was: OCaml general)
Related to: #4623

Bug description

The following code causes OCaml (e.g. ocamlc or ocamlopt) to fail with

Fatal error: exception Stack_overflow

type 'a s = 'a

module M : sig
type 'a t = private 'a s
constraint 'a = [< A] end = struct type 'a t = 'a s constraint 'a = [< A]
end

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commented Aug 1, 2008

Comment author: @xavierleroy

With CVS trunk, this definition is accepted at toplevel, but causes the following problem if put in .ml without .mli and compiled with ocamlc:

File "foo.ml", line 1, characters 0-1:
Error: The implementation foo.ml
does not match the interface (inferred signature):
Modules do not match:
sig type 'a t = 'a M.t constraint 'a = [< A ] end is not included in sig type 'a t = private 'a s constraint 'a = [< A ] end
Type declarations do not match:
type 'a t = 'a M.t constraint 'a = [< A ] is not included in type 'a t = private 'a s constraint 'a = [< A ]

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commented Dec 12, 2008

Comment author: @garrigue

The second problem (reported by Xavier) is similar to PR4623, and was fixed for 3.11 in includecore.ml. (Looks like I missed the 1st report with my holidays..)

The first bug is specific to 3.10 (doesn't occur in 3.11).
With the CVS version it no longer causes a stack overflow... just a non-terminating computation. Should look into it.
Note that it is fundamentally different: it is a private row in 3.10, but a private abbreviation in 3.11. While the 3.11 semantics makes sense (use a private abbreviation to hide the representation of t), the 3.10 semantics does not make sense in this example: it should just be equivalent to writing "type 'a t = private [< `A]", which works ok. So this is really only about making the compiler terminate even on meaningless code.

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commented Apr 27, 2010

Comment author: @garrigue

I was only keeping this one around because of 3.10, but since it went out of support a while ago, it seems ok to close this issue.

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