(foreign_library): support (enabled_if) (#9914)

Signed-off-by: Nicolás Ojeda Bär <[email protected]>

doc/changes/9914.md

@@ -0,0 +1,2 @@
+- The `(foreign_library)` stanza now supports the `(enabled_if)` field.  (#9914,
+  @nojb)

doc/reference/foreign.rst

@@ -138,6 +138,7 @@ described in :ref:`foreign-sandboxing`, or ask Dune to build it via the
     (foreign_library
      (archive_name arch1)
      (language c)
+     (enabled_if true)
      (names src4 src5)
      (include_dir headers))
 
@@ -147,10 +148,11 @@ object files into an archive ``arch1``, whose full name is typically
 ``libarch1.a`` for static linking and ``dllarch1.so`` for dynamic
 linking.
 
-The ``foreign_library`` stanza supports all :ref:`foreign-stubs` fields plus
-the ``archive_name`` field, which specifies the archive's name. You can refer
+The ``foreign_library`` stanza supports all :ref:`foreign-stubs` fields.
+The ``archive_name`` field specifies the archive's name. You can refer
 to the same archive name from multiple OCaml libraries and executables, so a
 foreign archive is a bit like a foreign library, hence the name of the stanza.
+The ``enabled_if`` field has the same meaning as in the :ref:`library` stanza.
 
 Foreign archives are particularly useful when embedding a library written in
 a foreign language and/or built with another build system. See

src/dune_rules/foreign.ml

@@ -253,15 +253,17 @@ module Library = struct
     { archive_name : Archive.Name.t
     ; archive_name_loc : Loc.t
     ; stubs : Stubs.t
+    ; enabled_if : Blang.t
     }
 
   let decode =
     let open Dune_lang.Decoder in
     fields
       (let+ archive_name_loc, archive_name =
          located (field "archive_name" Archive.Name.decode)
-       and+ stubs = Stubs.decode_stubs ~for_library:true in
-       { archive_name; archive_name_loc; stubs })
+       and+ stubs = Stubs.decode_stubs ~for_library:true
+       and+ enabled_if = Enabled_if.decode ~allowed_vars:Any ~since:(Some (3, 14)) () in
+       { archive_name; archive_name_loc; stubs; enabled_if })
   ;;
 
   include Stanza.Make (struct

src/dune_rules/foreign.mli

@@ -157,6 +157,7 @@ module Library : sig
     { archive_name : Archive.Name.t
     ; archive_name_loc : Loc.t
     ; stubs : Stubs.t
+    ; enabled_if : Blang.t
     }
 
   val decode : t Dune_lang.Decoder.t

src/dune_rules/gen_rules.ml

@@ -121,8 +121,10 @@ end = struct
           rules)
         enabled_if
     | Foreign.Library.T lib ->
-      let+ () = Lib_rules.foreign_rules lib ~sctx ~dir ~dir_contents ~expander in
-      empty_none
+      Expander.eval_blang expander lib.enabled_if
+      >>= if_available (fun () ->
+        let+ () = Lib_rules.foreign_rules lib ~sctx ~dir ~dir_contents ~expander in
+        empty_none)
     | Executables.T exes ->
       Expander.eval_blang expander exes.enabled_if
       >>= if_available (fun () ->

test/blackbox-tests/test-cases/foreign-library.t

@@ -904,3 +904,50 @@ Testsuite for the (foreign_library ...) stanza.
   Leaving directory 'stubs_in_libs'
   $ stubs_in_libs/_build/default/main.exe
   12
+
+--------------------------------------------------------------------------------
+* Test (enabled_if)
+
+  $ mkdir -p enabled_if
+  $ cat >enabled_if/dune-project <<EOF
+  > (lang dune 3.13)
+  > EOF
+  $ cat >enabled_if/lib.c <<EOF
+  > int foo(void) { return 0; }
+  > EOF
+  $ cat >enabled_if/dune <<EOF
+  > (foreign_library
+  >  (archive_name lib)
+  >  (language c)
+  >  (enabled_if (<> %{env:ENABLE=} "0"))
+  >  (names lib))
+  > EOF
+  $ dune build --root enabled_if
+  Entering directory 'enabled_if'
+  File "dune", line 4, characters 1-37:
+  4 |  (enabled_if (<> %{env:ENABLE=} "0"))
+       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  Error: 'enabled_if' is only available since version 3.14 of the dune
+  language. Please update your dune-project file to have (lang dune 3.14).
+  Leaving directory 'enabled_if'
+  [1]
+  $ cat >enabled_if/dune-project <<EOF
+  > (lang dune 3.14)
+  > EOF
+  $ cat >>enabled_if/dune <<EOF
+  > (library
+  >  (name lib)
+  >  (foreign_archives lib))
+  > EOF
+  $ ENABLE=1 dune build --root enabled_if
+  Entering directory 'enabled_if'
+  Leaving directory 'enabled_if'
+  $ ENABLE=0 dune build --root enabled_if
+  Entering directory 'enabled_if'
+  File "dune", line 6, characters 0-45:
+  6 | (library
+  7 |  (name lib)
+  8 |  (foreign_archives lib))
+  Error: No rule found for liblib.a
+  Leaving directory 'enabled_if'
+  [1]