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Typechecker overflow the stack on cyclic type annotation after matching on a GADT #6768

vicuna opened this issue Feb 2, 2015 · 1 comment


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commented Feb 2, 2015

Original bug ID: 6768
Reporter: darktenaibre
Assigned to: @garrigue
Status: closed (set by @xavierleroy on 2016-12-07T10:47:10Z)
Resolution: fixed
Priority: normal
Severity: minor
Version: 4.02.1
Fixed in version: 4.02.2+dev / +rc1
Category: typing
Monitored by: @hcarty

Bug description

The following make the typechecker loop and eventually overflow, while 4.01.0 fails saying the type annotation d is cyclic (which is correct).

Steps to reproduce

type _ prod =
| Prod : ('a * 'y) prod

let f : type t. t prod -> _ =
function Prod -> let module M =
type d = d * d
end in ()

Additional information

Removing the pattern matching, simplifying either the GADT constraint or the type declaration (e.g. "type d = d") or removing the typing constraint/abstraction on f yields the correct error message.


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commented Feb 5, 2015

Comment author: @garrigue

Fixed in trunk and 4.02.2 at revisions 15810 and 15811.

The problem was a forgotten wrap_trace_gadt_instance in Typedecl,check_well_founded.

@vicuna vicuna closed this Dec 7, 2016

@vicuna vicuna added the typing label Mar 14, 2019

@vicuna vicuna added the bug label Mar 20, 2019

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