Restore compatibility with 4.02

[nojb]

I did some brief testing on my side, but would appreciate confirmation from some other dev (especially if this is not being tested in the CI).

[ejgallego]

Can you add a changelog entry ?

[ejgallego]

I've tested a backport of this on lwt_react.1.1.5 + ocaml-base-compiler.4.02.3 which is the failure @kit-ty-kate reported.

Unfortunately it doesn't work:

#=== ERROR while compiling lwt_react.1.1.5 ====================================#
# context     2.1.0 | linux/x86_64 | ocaml-base-compiler.4.02.3 | https://opam.ocaml.org#ccfbafd8
# path        ~/.opam/dev-402/.opam-switch/build/lwt_react.1.1.5
# command     ~/.opam/opam-init/hooks/sandbox.sh build dune build -p lwt_react -j 15
# exit-code   1
# env-file    ~/.opam/log/lwt_react-44273-2f38c9.env
# output-file ~/.opam/log/lwt_react-44273-2f38c9.out
### output ###
# Error: Syntax error: attributes not expected.
# [...]
# (cd src/ppx && /home/egallego/.opam/dev-402/bin/ocaml -I +compiler-libs /home/egallego/.opam/dev-402/.opam-switch/build/lwt_react.1.1.5/_build/.dune/default/src/ppx/dune.ml)
# File "/home/egallego/.opam/dev-402/.opam-switch/build/lwt_react.1.1.5/_build/.dune/default/src/ppx/dune.ml", line 27, characters 0-457:
# Error: Syntax error: attributes not expected.
#        ocaml (internal) (exit 2)
# (cd src/domain && /home/egallego/.opam/dev-402/bin/ocaml -I +compiler-libs /home/egallego/.opam/dev-402/.opam-switch/build/lwt_react.1.1.5/_build/.dune/default/src/domain/dune.ml)
# File "/home/egallego/.opam/dev-402/.opam-switch/build/lwt_react.1.1.5/_build/.dune/default/src/domain/dune.ml", line 27, characters 0-457:
# Error: Syntax error: attributes not expected.
#        ocaml (internal) (exit 2)
# (cd src/core && /home/egallego/.opam/dev-402/bin/ocaml -I +compiler-libs /home/egallego/.opam/dev-402/.opam-switch/build/lwt_react.1.1.5/_build/.dune/default/src/core/dune.ml)
# File "/home/egallego/.opam/dev-402/.opam-switch/build/lwt_react.1.1.5/_build/.dune/default/src/core/dune.ml", line 27, characters 0-457:
# Error: Syntax error: attributes not expected.

[nojb]

Unfortunately it doesn't work:

OK, let me try something else.

[kit-ty-kate]

Could the tests be enabled for 4.02 ?

[nojb]

Unfortunately it doesn't work:

OK, let me try something else.

I pushed an alternative fix that should work on 4.02.

[nojb]

Just thinking about this again, perhaps we want to simply pass -w -3 on the command line when executing the OCaml script (instead of disabling the warning just for Toplevel.directive_table)? That way we protect ourselves against any future deprecation as well, no?

[nojb]

Just thinking about this again, perhaps we want to simply pass -w -3 on the command line when executing the OCaml script (instead of disabling the warning just for Toplevel.directive_table)? That way we protect ourselves against any future deprecation as well, no?

The downside is that 1) we may miss deprecations if we are not warned about them, and 2) the deprecation alerts will also not be triggered for the user code.

[ejgallego]

I confirm it works, thanks Nicolas. What to do w.r.t. "-w -3", that I'm unsure, indeed seems like a delicate tradeoof.

[nojb]

I confirm it works, thanks Nicolas. What to do w.r.t. "-w -3", that I'm unsure, indeed seems like a delicate tradeoof.

OK, let's leave that for later and merge this PR as it is.