[BUG] Mention std_exit in separate compilation instructions

[dbuenzli]

Separate compilation instructions should mention that to get exactly the same results as what is done by whole program compilation one should add a compilation of std_exit at the end of the link instruction. Otherwise do_at_exit will not be called which means at_exit functions won't either.

This may not be a problem if you don't use Sys.at_exit handlers but it may lead to different visible program behaviour: in particular the Stdlib.flush_all funcction won't be called at program exit.

Whole program:

> echo "let () = print_string {|bla|}" > main.ml
> ocamlc -o main.byte main.ml 
> js_of_ocaml -o main.js main.byte 
> node main.js
bla
>

Separate compilation (according to current instructions):

> js_of_ocaml build-runtime -o ocaml-rt.js 
> js_of_ocaml compile -o stdlib.js $(opam var lib)/ocaml/stdlib.cma
> js_of_ocaml compile -o main.js main.cmo 
> js_of_ocaml link -o a.js ocaml-rt.js stdlib.js main.js 
> node a.js
> 

Adding a compilation of std_exit.cmo:

> js_of_ocaml compile -o std_exit.js $(opam var lib)/ocaml/std_exit.cmo 
> js_of_ocaml link -o a.js ocaml-rt.js stdlib.js main.js std_exit.js    
> node a.js
bla

[hhugo]

One should also fix dune compilation rules

[dbuenzli]

Yes I opened an issue there. See the cross refs.