Expected Behavior

We have:

(test
 (name test)
 (package eio_linux)
 (enabled_if (= %{system} "linux"))
 (modules test)
 (libraries alcotest eio_linux))

I expect this stanza to be ignored on macos. However, dune tries to build test.ml anyway. If I delete the stanza, it skips the file, as expected (reported by a macos user and tested on Linux by changing "linux" to "foobar" and confirming that it still tries to build it).

I consulted the dune documention for (test):

• (test) says "the test stanza is the singular form of tests"
• (tests) says "The optional fields supported are a subset of the alias and executables fields. In particular, all fields except for public_names are supported from the executables stanza. Alias fields apart from name are allowed."
• (executables) says "(enabled_if <blang expression>) is the same as the corresponding field of library."
• (library) says "The condition is specified using the Boolean Language, and the field allows for the %{os_type} variable, which is expanded to the type of OS being targeted by the current build."

However, I believe system is supposed to work. If I try a different variable name, dune says Error: Unknown variable %{baz}, which I infer to mean that it does understand system.

/cc @polytypic

Reproduction

$ ls
dune  dune-project  test.ml

$ cat dune
(test
 (name test)
 (enabled_if (= %{system} "foobar"))
 (modules test))

$ cat dune-project 
(lang dune 3.0)

$ cat test.ml 
BROKEN

$ dune build @all
File "test.ml", line 1, characters 0-6:
1 | BROKEN
    ^^^^^^
Error: Unbound constructor BROKEN

Specifications

• Version of dune (output of dune --version): 3.6.1
• Version of ocaml (output of ocamlc --version): 5.0.0
• Operating system (distribution and version): Debian 11.6