bigarray compatibility library not linked

[aantron]

After ocaml/ocaml#1685, projects requiring compatibility with OCaml < 4.06 that use the Bigarray.*.map_file functions need to link in the bigarray library. However, this seems to be broken on OCaml 4.08 and Dune 1.7.0 (though I suspect it's not specific to this Dune version). Bigarray seems to resolve to the stdlib instance rather than the bigarray one, resulting in

Error: Unbound value Bigarray.Array1.map_file

Here is a sample project reproducing the issue.

• Changing map_file to any other function from Bigarray.Array1 makes compilation succeed, so an instance of Bigarray is being linked.
• Compilation succeeds on 4.07 (rather, it fails with another error, but only after first triggering a deprecation warning on map_file, demonstrating resolution).
• Adding or removing (libraries bigarray) has no effect on the outcome.

[avsm]

@TheLortex has also been running into this as part of mirage/mirage#969

[rgrinberg]

@nojb any idea?

[rgrinberg]

Hmm, testing this out a bit it seems like it's not an issue with dune. In 4.07, I get this in the REPL:

01:37 .opam rlwrap ocaml
        OCaml version 4.07.1

# Bigarray.Array1.map_file;;
Warning 3: deprecated: Bigarray.Array1.map_file
Use [array1_of_genarray (Unix.map_file ...)] instead.
Note that Bigarray.Array1.map_file raises Sys_error while
Unix.map_file raises Unix_error.
Error: Reference to undefined global `Bigarray'

While in 4.08, I get:

01:38 .opam rlwrap ocaml
        OCaml version 4.08.0+beta1

# Bigarray.Array1.map_file;;
Error: Unbound value Bigarray.Array1.map_file
#

[nojb]

Can you check if there is a bigarray.cmi in ocamlc -where?

[nojb]

I am guessing that ocaml/ocaml#2041 may be involved: as per the explanation in that PR the initial environment is now built as:

env <- add_dir(env, stdlib_dir)
env <- open(env, Stdlib)

which would effectively hide any module in stdlib_dir with the same name as a submodule of Stdlib.

@diml ?

[nojb]

@rgrinberg can you try doing rlwrap ocaml -I + and repeating the experiment?

[rgrinberg]

Can you check if there is a bigarray.cmi in ocamlc -where?

There is.

can you try doing rlwrap ocaml -I + and repeating the experiment?

That seems to fix things:

04:26 .opam rlwrap ocaml -I +
        OCaml version 4.08.0+beta1

# Bigarray.Array1.map_file;;
Alert deprecated: Bigarray.Array1.map_file
Use [array1_of_genarray (Unix.map_file ...)] instead.
Note that Bigarray.Array1.map_file raises Sys_error while
Unix.map_file raises Unix_error.
Error: Reference to undefined global `Bigarray'

[ghost]

This is in fact a bug in the compiler. It is fixed in ocaml/ocaml#2256