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module alias breaks backward compatibility wrt separate compilation #6661

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vicuna opened this issue Nov 18, 2014 · 2 comments
Closed

module alias breaks backward compatibility wrt separate compilation #6661

vicuna opened this issue Nov 18, 2014 · 2 comments
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@garrigue
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@vicuna
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vicuna commented Nov 18, 2014

Original bug ID: 6661
Reporter: @ygrek
Assigned to: @garrigue
Status: closed (set by @xavierleroy on 2016-12-07T10:36:55Z)
Resolution: not fixable
Priority: normal
Severity: major
Version: 4.02.1
Fixed in version: 4.03.0+dev / +beta1
Category: ~DO NOT USE (was: OCaml general)
Monitored by: @hcarty

Bug description

$ cat a.ml
module X = Xmlm
type x = X.encoding

$ cat b.ml
type q = A.X.encoding

$ opam config exec --switch 4.01.0 -- bash -c 'ocamlc -I $(ocamlfind query xmlm) -c a.ml && ocamlc -c b.ml'

$ opam config exec --switch 4.02.1 -- bash -c 'ocamlc -I $(ocamlfind query xmlm) -c a.ml && ocamlc -c b.ml'
File "b.ml", line 1, characters 9-21:
Error: Unbound type constructor A.X.encoding

Steps to reproduce

IIUC previous versions of compiler expanded the module alias and so the other module had all the information of module structure contents, but nowadays it sees only the module alias and cannot dig into it without cmi.
@vicuna
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vicuna commented Nov 18, 2014

Comment author: @garrigue

The whole point of module alias being avoiding to duplicated information in the cmi's, this cannot be avoided: the signature of Xmlm is no longer included in a.cmi.
A workaround is to write an explicit mli.
(Changes didn't document this incompatibility; fixed in 15597)

@vicuna
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vicuna commented Nov 18, 2014

Comment author: @ygrek

Another obvious fix is just provide the include path for compiler invocation for all modules using the alias.

@vicuna vicuna closed this as completed Dec 7, 2016
@vicuna vicuna added the bug label Mar 20, 2019
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