Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Soundness bug with non-generalized type variable and functors #7414

Closed
vicuna opened this issue Nov 16, 2016 · 2 comments
Closed

Soundness bug with non-generalized type variable and functors #7414

vicuna opened this issue Nov 16, 2016 · 2 comments
Assignees

Comments

@vicuna
Copy link

@vicuna vicuna commented Nov 16, 2016

Original bug ID: 7414
Reporter: @lpw25
Assigned to: @garrigue
Status: resolved (set by @garrigue on 2016-11-21T13:22:14Z)
Resolution: fixed
Priority: normal
Severity: minor
Version: 4.04.0
Fixed in version: 4.05.0 +dev/beta1/beta2/beta3/rc1
Category: typing
Related to: #6752
Monitored by: @gasche @yallop

Bug description

The interplay between non-generalized type variables and functors seems ill defined and unsound. Using first-class modules we can get a segfault:

  module type T = sig
    type t
    val x : t
    val show : t -> string
  end

  module Int = struct
    type t = int
    let x = 0
    let show x = string_of_int x
  end

  module String = struct
    type t = string
    let x = "Hello"
    let show x = x
  end

  let switch = ref true

  module Choose () = struct
    module Choice =
      (val if !switch then (module Int : T)
           else (module String : T))
    let r = ref (ref [])
  end

  module type S = sig
    module Choice : T
    val r : Choice.t list ref ref
  end

  module Force (X : functor () -> S) = struct end

  module M = Choose ()

  let () = switch := false

  module N = Choose ()

  let () = N.r := !M.r

  module Ignore = Force(Choose)

  module M' = (M : S)

  let () = (!M'.r) := [M'.Choice.x]

  module N' = (N : S)

  let () = List.iter (fun x -> print_string (N'.Choice.show x)) !(!N'.r)
@vicuna
Copy link
Author

@vicuna vicuna commented Nov 19, 2016

Comment author: @garrigue

I've created a pull-request #929 with a fix.
Note that the current fix is not very efficient, so I will revise it before merging,
to use an iterator rather than Subst.modtype.

@vicuna
Copy link
Author

@vicuna vicuna commented Nov 21, 2016

Comment author: @garrigue

Merged the pull request in commit 2bd2296.
Now handled by a visit of the signature rather than by Subst.

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Projects
None yet
Development

No branches or pull requests

2 participants