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Unsoundness when -rectypes fails to detect non-contractive type #6870

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vicuna opened this issue May 14, 2015 · 4 comments

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commented May 14, 2015

Original bug ID: 6870
Reporter: @stedolan
Assigned to: @garrigue
Status: closed (set by @xavierleroy on 2016-12-07T10:49:21Z)
Resolution: fixed
Priority: normal
Severity: minor
Version: 4.02.1
Fixed in version: 4.02.2+dev / +rc1
Category: typing
Child of: #5343
Monitored by: @gasche @yallop

Bug description

OCaml 4.02.1 correctly rejects this dubious definition of a possibly non-contractive recursive type:

module type T = sig type 'a t end
module Fix (T : T) = struct type r = r T.t end

However, it accepts the following equivalent definition:

module Fix (T : T) = struct type r = ('r T.t) as 'r end

I think this is substantially the same issue as #5343. For a concrete example of how this leads to a segfault, see:

https://gist.github.com/stedolan/b5fe862fd350110ffa8e
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commented May 17, 2015

Comment author: @garrigue

Indeed, one must fix the occur check too...

Fixed in trunk and 4.02 at revisions 16122 and 16123.

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commented May 17, 2015

Comment author: @gasche

It seems that you didn't commit the .reference file; at least the test pr6870_bad fails in the testsuite.

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commented May 17, 2015

Comment author: @garrigue

This is an ok/bad test. There is no need for a reference file.
On my machine, the test succeeds (i.e. compilation causes an error).

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commented May 18, 2015

Comment author: @garrigue

Had just committed in the testsuite directory...
Really fixed at revision 16126.

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