[BUG] Assertion failure in separate compilation

[dbuenzli]

Describe the bug
The following (wrong) simple source file triggers an assertion failure.

> mkdir /tmp/bug
> cd /tmp/bug
> cat - > prop.ml
type t
type prop
external set : t -> prop -> t -> unit = "caml_js_get"
let set_if_some o p = function None -> () | Some v -> set o p v
> ocamlc -c prop.ml 
> js_of_ocaml compile prop.cmo 
js_of_ocaml: You found a bug. Please report it at https://github.com/ocsigen/js_of_ocaml/issues :
Error: File "compiler/lib/generate.ml", line 844, characters 13-19: Assertion failed
Raised at file "compiler/lib/generate.ml", line 844, characters 13-25
Called from file "compiler/lib/generate.ml", line 1190, characters 24-41
Called from file "compiler/lib/generate.ml", line 1239, characters 43-82
Called from file "compiler/lib/generate.ml", line 1300, characters 27-67
Called from file "compiler/lib/generate.ml", line 1301, characters 31-70
Called from file "compiler/lib/generate.ml", line 1342, characters 6-74
Called from file "compiler/lib/generate.ml", line 1586, characters 15-70
Called from file "compiler/lib/generate.ml", line 1588, characters 29-42
Called from file "compiler/lib/generate.ml", line 1636, characters 14-29
Called from file "compiler/lib/generate.ml", line 1666, characters 10-226
Called from file "compiler/lib/generate.ml", line 1473, characters 12-232
Called from file "compiler/lib/generate.ml", line 1878, characters 4-85
Called from file "compiler/lib/generate.ml", line 1018, characters 16-40
Called from file "compiler/lib/generate.ml", line 1239, characters 43-82
Called from file "compiler/lib/generate.ml", line 1300, characters 27-67
Called from file "compiler/lib/generate.ml", line 1342, characters 6-74
Called from file "compiler/lib/generate.ml", line 1659, characters 21-79
Called from file "compiler/lib/generate.ml", line 1473, characters 12-232
Called from file "compiler/lib/generate.ml", line 1659, characters 21-79
Called from file "compiler/lib/generate.ml", line 1473, characters 12-232
Called from file "compiler/lib/generate.ml", line 1878, characters 4-85
Called from file "compiler/lib/generate.ml", line 1918, characters 12-40
Called from file "compiler/lib/generate.ml", line 1930, characters 10-37
Called from file "compiler/lib/driver.ml" (inlined), line 83, characters 21-26
Called from file "compiler/lib/driver.ml", line 444, characters 2-186
Called from file "compiler/lib/driver.ml" (inlined), line 83, characters 21-26
Called from file "compiler/lib/driver.ml", line 444, characters 2-204
Called from file "compiler/lib/driver.ml" (inlined), line 83, characters 21-26
Called from file "compiler/lib/driver.ml", line 444, characters 2-218
Called from file "compiler/lib/driver.ml" (inlined), line 83, characters 21-26
Called from file "compiler/lib/driver.ml", line 444, characters 2-232
Called from file "compiler/lib/driver.ml" (inlined), line 83, characters 21-26
Called from file "compiler/lib/driver.ml", line 444, characters 2-296
Called from file "compiler/lib/stdlib.ml", line 585, characters 11-15
Re-raised at file "compiler/lib/stdlib.ml", line 588, characters 9-16
Re-raised at file "compiler/lib/stdlib.ml", line 594, characters 6-15
Called from file "compiler/bin-js_of_ocaml/compile.ml", line 172, characters 8-625
Called from file "compiler/bin-js_of_ocaml/compile.ml", line 258, characters 8-49
Called from file "cmdliner_term.ml", line 25, characters 19-24
Called from file "cmdliner.ml", line 117, characters 32-39
Called from file "cmdliner.ml", line 147, characters 18-36
Called from file "cmdliner.ml", line 265, characters 22-48
Called from file "compiler/bin-js_of_ocaml/js_of_ocaml.ml", line 48, characters 4-225

Expected behavior
Maybe something more helpful. In this particular of course the primitive is wrong. It should be caml_js_set

Versions

ocamlc -version
4.09.0
js_of_ocaml --version
3.6.0

[hhugo]

Correct me if I'm wrong but this is not specific to separate compilation. Maybe update title.