Inline tests: add node_flags

[vouillon]

node is used to run inline tests generated by Js_of_ocaml. This allows to pass specific flags to this program.
So this adds an environment field (js_of_ocaml (node_flags <flags>) and a per library field (inline_tests (node_flags <flags>)).
Maybe that should rather be (inline_tests (js_of_ocaml (node_flags <flags>))) to emphasize that this only apply in js mode?
I still need to update the documentation.

[hhugo]

node is not only used for inline_tests, it's also used for running tests from (tests ..) stanza.

$ ag jsoo_rules.runner
src/dune_rules/inline_tests.ml
237:        | Javascript -> Some Jsoo_rules.runner

src/dune_rules/test_rules.ml
44:              | `js -> Some Jsoo_rules.runner

Also, I wonder if it would be better to allow full customization of the js runner.

A user could then do (js_of_ocaml (js_runner node --jitless %{input-file} %))
or use another js vm.

There exist a workaround for running a js vm other than node but it's not very satisfactory.
Here is what's used in the tezos codebase.

(env
 (_
  (binaries (%{workspace_root}/src/tooling/node_wrapper.exe as node))))

[vouillon]

There exist a workaround for running a js vm other than node but it's not very satisfactory. Here is what's used in the tezos codebase.

(env
 (_
  (binaries (%{workspace_root}/src/tooling/node_wrapper.exe as node))))

Oh, I already do this to be able to write run node without having to specify options each time. But I did not realize that it affected inline tests as well. So, I don't really need this change after all.

Maybe a variable js_runner could be useful?

Dune seems to allow to specify flags rather than whole commands. For instance, there is a CC variable but only a c_flags environment setting. I'm wondering whether there is a strong reason for that, or whether there simply has not yet been any good reason to select a different executable.

[hhugo]

@rgrinberg, do you have any opinion ?

[rgrinberg]

do you have any opinion ?

About the js_runner flag? Yeah it seems like a useful thing to have.

For instance, there is a CC variable but only a c_flags environment setting. I'm wondering whether there is a strong reason for that, or whether there simply has not yet been any good reason to select a different executable.

People have asked to change the executable before. I don't think anyone would object such a way to set the C compiler.

[rgrinberg]

@hhugo what's the status of this?

[vouillon]

@rgrinberg I need to understand how to add a variable js_runner, which would be a lot more useful than having just a node_flags option. Maybe I should close this PR for now?