[BUG] Produced code invariably requires node:fs (dead code)

[xzxzzxzxzca]

Describe the bug
Let's say we have the simplest possible OCaml program:

let () =
  print_endline "Hello, World!"

Which we compile using jsoo:

(executable
 (name hello)
 (modes js)

 (modules hello)

 (js_of_ocaml
  (flags
    --opt 3
    --enable deadcode
    --enable globaldeadcode
  ))
)

Although the program performs no file operations, the generated code still requires node:fs and contains filesystem functions, even on the highest optimization level, even when asked to eliminate all dead code, even with --profile release.

This is extremely problematic for deployments to React Native platforms, where the module does not exist.

Expected behavior
Filesystem functions should not be included unless actually used.

As an alternative, the module could be loaded lazily.

Versions
ocamlc: 5.2.1
js_of_ocaml: 5.9.1

[hhugo]

Try --target-env browser

[xzxzzxzxzca]

@hhugo this indeed removes the dependency on node:fs (although, only with --profile release, otherwise still there, WUT).

However, this brings in references to window which, again, is not there in RN environment. RN is like node, but fewer standard modules.

However, this also creates issues with references to JS object implemented in Ocaml and accessed from another library's (javascript_files ...). Sorry, I can't immediately provide a minimal reproducer.

[hhugo]

(although, only with --profile release, otherwise still there, WUT).

You need to set the flag when building the runtime
(build_runtime_flags (:standard --target-env browser))

[hhugo]

Although the program performs no file operations,

Printing to stdout with print_endline uses node:fs.writeSync when running on node

[xzxzzxzxzca]

Printing to stdout with print_endline uses node:fs.writeSync when running on node

Is there a way to somehow force non-inclusion of a module (e.g. node:fs) and a compilation error when one is required by the code?

Or is there a way to trace down which libraries/modules/functions pull in dependencies like the one we are talking about?

@hhugo

[hhugo]

Is there a way to somehow force non-inclusion of a module (e.g. node:fs)

--target-env browser

and a compilation error when one is required by the code?

no

Or is there a way to trace down which libraries/modules/functions pull in dependencies like the one we are talking about?

manual inspection

However, this brings in references to window which, again, is not there in RN environment.

I don't know where this reference come from. I don't think it's related to --target-env browser

I don't know the constraints impose by react native. Maybe you can update jsoo to support --target-env react-native.

[xzxzzxzxzca]

(although, only with --profile release, otherwise still there, WUT).

You need to set the flag when building the runtime (build_runtime_flags (:standard --target-env browser))

This, in combination with (flags --target-env nodejs), seems to solve the issue for me.
Thanks @hhugo I think we can close this for now

[rizo]

I noticed a related issue. My js files contain references to node even when compiled for the browser target.

This only happens with the dev profile. With release, the issue is gone.

dune:

(executable
 (name test)
 (modes js)
 (js_of_ocaml
  (flags (:standard --target-env browser))
  (build_runtime_flags (:standard --target-env browser))))

Produces a js file with "node:util":

$ dune build tests/test.bc.js; cat _build/default/tests/test.bc.js | grep 'node:util'
    const util = require("node:util");

Versions

$ dune --version
3.20.2

$ dune exec -- js_of_ocaml --version
6.2.0  

If this is something new, happy to open a separate issue and help with investigation.