fix(x-compilation): take the default findlib path context into account

Signed-off-by: Antonio Nuno Monteiro <anmonteiro@gmail.com>

Author: anmonteiro

src/dune_rules/findlib/findlib.ml

@@ -100,7 +100,7 @@ module Vars = struct
 
   let empty = String.Map.empty
 
-  let superpose = String.Map.superpose
+  let union = String.Map.union
 end
 
 module Config = struct
@@ -116,7 +116,6 @@ module Config = struct
       ; ("preds", Ps.to_dyn preds)
       ]
 
-
   let load config_file =
     let load p =
       let+ meta = Meta.load ~name:None p in
@@ -141,7 +140,12 @@ module Config = struct
                 let p = Path.Outside_build_dir.relative config_dir p in
                 load p)
           in
-          List.fold_left all_vars ~init:vars ~f:Vars.superpose
+          List.fold_left all_vars ~init:vars ~f:(fun acc vars ->
+              Vars.union acc vars ~f:(fun _ (x : Rules.t) y ->
+                  Some
+                    { Rules.set_rules = x.set_rules @ y.set_rules
+                    ; add_rules = x.add_rules @ y.add_rules
+                    }))
         | Error _ -> Memo.return vars)
       | Ok false | Error _ -> Memo.return vars
     in

test/blackbox-tests/test-cases/custom-cross-compilation/cross-compilation-ocamlfind.t

@@ -63,17 +63,24 @@ Dune should be able to find it too
 
   $ dune build --root=app @install -x foo
   Entering directory 'app'
-  File "dune", line 6, characters 12-18:
-  6 |  (libraries libdep))
-                  ^^^^^^
-  Error: Library "libdep" not found.
-  -> required by _build/default/.gen.eobjs/byte/dune__exe__Gen.cmi
-  -> required by _build/default/.gen.eobjs/native/dune__exe__Gen.cmx
-  -> required by _build/default/gen.exe
-  -> required by _build/default.foo/foo.ml
-  -> required by _build/install/default.foo/lib/repro/foo.ml
-  -> required by _build/default.foo/repro-foo.install
-  -> required by alias install (context default.foo)
   Leaving directory 'app'
-  [1]
 
+Library is built in the target context
+
+  $ ls app/_build/default.foo
+  META.repro
+  foo.ml
+  repro-foo.install
+  repro.a
+  repro.cma
+  repro.cmxa
+  repro.cmxs
+  repro.dune-package
+  repro.ml-gen
+
+Executable was built in the host context
+
+  $ ls app/_build/default
+  gen.exe
+  gen.ml
+  gen.mli