Recursive value check too relaxed -- produces segfault

[vicuna]

Original bug ID: 7706
Reporter: @lpw25
Assigned to: @gasche
Status: resolved (set by @gasche on 2018-04-10T10:35:19Z)
Resolution: fixed
Priority: normal
Severity: minor
Version: 4.06.0
Fixed in version: 4.07.0+dev/beta2/rc1/rc2
Category: typing
Related to: #7768
Monitored by: @nojb @yallop

Bug description

The new recursive value check is too relaxed in how it treats [let] when it decides if a recursive definition's size can be calculated in advance:

        OCaml version 4.06.0+beta1

# let rec x =
    let y = if false then (fun z -> 1) else (fun z -> x 4 + 1) in
    y;;
    val x : int -> int = <fun>
# x 42;;

Process ocaml-toplevel segmentation fault

[vicuna]

Comment author: @gasche

Good catch!

The problem is that identifiers are considered to be static size; in your example, "y" is considered static-sized, so the definition is accepted. This is clearly wrong for local identifiers, but it is not clear to me why it should be correct for non-local identifiers (or for identifiers defined in the same letrec-block).

[vicuna]

Comment author: @gasche

Tentative fix: #1565

[vicuna]

Comment author: @gasche

Fixed in 4.07 by the above pull request.

A followup issue was found by Leo and is tracked by #7768.