`:standard` in an `:include`d file is ignored

[bclement-ocp]

Expected Behavior

Using a :standard atom in an :include file should either:

• Handle the :standard atom in the same way as if the contents of file had been inlined to replace the :include form, or
• If that is not possible, raise an error indicating that :standard is not supported inside an :included file (in the same way that trying to use an :include in an :include is an error).

Actual Behavior

Using a :standard atom in an :include file is ignored (or maybe does not resolve to the correct flags, I am not sure).

Reproduction

Consider the following dune file:

(env
 (dev
  (flags (:standard -does-not-exist))))

(library
 (name include_standard)
 (modules)
 (flags (:include flags.sexp)))

(library
 (name standard)
 (modules)
 (flags (:standard)))

(rule
 (action
  (write-file flags.sexp "(:standard)")))

dune provides the following outputs:

$ dune build standard.a
File "dune", lines 10-13, characters 0-58:
10 | (library
11 |  (name standard)
12 |  (modules)
13 |  (flags (:standard)))
ocamlopt.opt: unknown option '-does-not-exist'.
Usage: ocamlopt <options> <files>
Try 'ocamlopt --help' for more information.
$ dune build include_standard.a

When using (flags (:standard)) (in the standard.a target), the bogus -does-not-exist flag from the environment is correctly used. But for the include_standard.a target, which goes through an :include, the flags from the environment are ignored.

Specifications

• Version of dune (output of dune --version): 3.20.2
• Version of ocaml (output of ocamlc --version): The OCaml toplevel, version 5.3.0
• Operating system (distribution and version): NixOS 25.11