No config flags in :standard. Always prepend to cc.

Signed-off-by: Ulysse Gérard <[email protected]>

src/dune/foreign_rules.ml

@@ -78,12 +78,18 @@ let build_c_or_cxx_file ~language ~sctx ~dir ~expander ~include_flags
   let flags =
     let ctx_flags =
       match language with
-      | Foreign.Language.C -> Fdo.c_flags ctx
+      | Foreign.Language.C ->
+        let cfg = ctx.ocaml_config in
+        List.concat
+          [ Ocaml_config.ocamlc_cflags cfg
+          ; Ocaml_config.ocamlc_cppflags cfg
+          ; Fdo.c_flags ctx
+          ]
       | Foreign.Language.Cxx -> Fdo.cxx_flags ctx
     in
     let flags = Foreign.Source.flags src in
     Super_context.foreign_flags sctx ~dir ~expander ~flags ~language
-    |> Build.map ~f:(List.append ctx_flags)
+    |> Build.map ~f:List.(rev_append (rev ctx_flags))
   in
   let output_param =
     match ctx.lib_config.ccomp_type with

src/dune/super_context.ml

@@ -2,9 +2,16 @@ open! Stdune
 open Import
 
 let default_context_flags (ctx : Context.t) =
-  let c = Ocaml_config.ocamlc_cflags ctx.ocaml_config in
+  (* TODO (v3) Current flag behavior is different when calling the C compiler or
+     the C++ compiler: 1.[ocamlc_cflags] and [ocamlc_cppflags] are always
+     prenpended to the C compiler arguments to reproduce [ocamlc]'s behavior, 2.
+     [ocamlc_cflags] are present in [:standard] and prepended to the C++
+     compiler arguments only if the user didn't redefined them (or used
+     [:standard] to extend them) *)
+  let c = [] in
   let cxx =
-    List.filter c ~f:(fun s -> not (String.is_prefix s ~prefix:"-std="))
+    Ocaml_config.ocamlc_cflags ctx.ocaml_config
+    |> List.filter ~f:(fun s -> not (String.is_prefix s ~prefix:"-std="))
   in
   Foreign.Language.Dict.make ~c ~cxx