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regression in type inference with 4.04.0+beta2 #7401

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vicuna opened this issue Nov 4, 2016 · 3 comments
Closed

regression in type inference with 4.04.0+beta2 #7401

vicuna opened this issue Nov 4, 2016 · 3 comments
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@garrigue
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bug duplicate typing
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4.05.0

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@vicuna
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vicuna commented Nov 4, 2016 •
edited by trefis

Original bug ID: 7401
Reporter: @c-cube
Assigned to: @garrigue
Status: closed (set by @garrigue on 2016-12-10T02:01:01Z)
Resolution: duplicate
Priority: normal
Severity: minor
Target version: 4.05.0 +dev/beta1/beta2/beta3/rc1
Category: typing
Duplicate of: #7313
Related to: #6752
Monitored by: @yallop

Bug description

A package that builds normally on 4.01, 4.02, 4.03 fails on 4.04.0+beta2 as follows:

# Error: The implementation src/core/Transform.ml
# [...]
#        ...
#        In module Features:
#        Values do not match:
#          val update_l : (key * '_a) list -> '_a M.t -> '_a M.t
#        is not included in
#          val update_l : (key * value) list -> t -> t
#        File "src/core/Transform.ml", line 58, characters 6-14:
#          Actual declaration

This is quite simple code, but it appears that, in the .ml file, the inferred type contains '_a variables that would later be bound to concrete types thanks to the .mli.

Steps to reproduce

opam sw 4.04.0+beta2
wget https://github.com/nunchaku-inria/nunchaku/archive/0.3.tar.gz
tar xvf 0.3.tar.gz
cd nunchaku-0.3
opam install ocamlfind containers sequence menhir
./configure --disable-random
make

should lead to this error.

Additional information

discovered in https://travis-ci.org/ocaml/opam-repository/jobs/173265123
@vicuna
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vicuna commented Nov 4, 2016

Comment author: @gasche

I just reproduced the (failure) behavior from the head of the 4.04 branch.

Looking at the *-marked entries in the Changelog, the one that seems related to is:

@vicuna
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vicuna commented Nov 4, 2016

Comment author: @damiendoligez

What I believe: the typechecker is now more strict because previous versions were unsound (or are believed to be unsound).

What I know: the new behaviour breaks very few programs and is easy to work around, so I've decided to release without looking for a fix.

@vicuna
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vicuna commented Dec 10, 2016

Comment author: @garrigue

Indeed, this is a consequence of the stricter typing of submodules.
#7414 is an example of why the previous approach was wrong.
I have some idea for allowing examples where the type can be trivially found in the mli, but it is harder than I thought first.

@vicuna vicuna closed this as completed Dec 10, 2016
@vicuna vicuna added this to the 4.05.0 milestone Mar 14, 2019
This was referenced Dec 10, 2016
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Closed
@vicuna vicuna added the bug label Mar 20, 2019
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