let module X = Path in … is not typed as a module alias

[vicuna]

Original bug ID: 6944
Reporter: @let-def
Assigned to: @garrigue
Status: closed (set by @xavierleroy on 2017-02-16T14:14:58Z)
Resolution: fixed
Priority: normal
Severity: minor
Version: 4.02.2
Fixed in version: 4.03.0+dev / +beta1
Category: typing
Monitored by: @hcarty

Bug description

Let-bound modules are never typed as module aliases.
This can cause scope escape issues.

Steps to reproduce

(* Fail without module alias *)

let f () =

let module S = String in
let module N = Map.Make(S) in
N.add "sum" 41 N.empty;;

Error: This expression has type int Map.Make(S).t
but an expression was expected of type int Map.Make(S).t
The type constructor Map.Make(S).t would escape its scope

(* Succeed with *)

let f () =

let module X = struct module S = String end in
let module N = Map.Make(X.S) in
N.add "sum" 41 N.empty;;
val f : unit -> int Map.Make(String).t =

[vicuna]

Comment author: @garrigue

Well spotted.
Fixed in trunk at revision 16412.