5 files changed, 50 insertions, 10 deletions
diff --git a/bytecomp/bytelink.ml b/bytecomp/bytelink.ml
index 90fcc0917a..79976dda15 100644
--- a/bytecomp/bytelink.ml
+++ b/bytecomp/bytelink.ml
@@ -19,6 +19,13 @@ open Misc
 open Config
 open Cmo_format
 
+module Dep = struct
+  type t = string * string
+  let compare = compare
+end
+
+module DepSet = Set.Make (Dep)
+
 type error =
   | File_not_found of filepath
   | Not_an_object_file of filepath
@@ -30,7 +37,7 @@ type error =
   | Cannot_open_dll of filepath
   | Required_module_unavailable of modname * modname
   | Camlheader of string * filepath
-  | Wrong_link_order of (modname * modname) list
+  | Wrong_link_order of DepSet.t
   | Multiple_definition of modname * filepath * filepath
 
 exception Error of error
@@ -90,11 +97,11 @@ let add_ccobjs origin l =
 
 let missing_globals = ref Ident.Map.empty
 let provided_globals = ref Ident.Set.empty
-let badly_ordered_dependencies : (string * string) list ref = ref []
+let badly_ordered_dependencies : DepSet.t ref = ref DepSet.empty
 
 let record_badly_ordered_dependency (id, compunit) =
-  badly_ordered_dependencies :=
-    ((Ident.name id), compunit.cu_name) :: !badly_ordered_dependencies
+  let dep = ((Ident.name id), compunit.cu_name) in
+  badly_ordered_dependencies := DepSet.add dep !badly_ordered_dependencies
 
 let is_required (rel, _pos) =
   match rel with
@@ -632,11 +639,11 @@ let link objfiles output_name =
     match Ident.Map.bindings missing_modules with
     | [] -> ()
     | (id, cu_name) :: _ ->
-        match !badly_ordered_dependencies with
-        | [] ->
+        if DepSet.is_empty !badly_ordered_dependencies
+        then
             raise (Error (Required_module_unavailable (Ident.name id, cu_name)))
-        | l ->
-            raise (Error (Wrong_link_order l))
+        else
+            raise (Error (Wrong_link_order !badly_ordered_dependencies))
   end;
   Clflags.ccobjs := !Clflags.ccobjs @ !lib_ccobjs; (* put user's libs last *)
   Clflags.all_ccopts := !lib_ccopts @ !Clflags.all_ccopts;
@@ -772,7 +779,8 @@ let report_error ppf = function
       fprintf ppf "Module `%s' is unavailable (required by `%s')" s m
   | Camlheader (msg, header) ->
       fprintf ppf "System error while copying file %s: %s" header msg
-  | Wrong_link_order l ->
+  | Wrong_link_order depset ->
+      let l = DepSet.elements depset in
       let depends_on ppf (dep, depending) =
         fprintf ppf "%s depends on %s" depending dep
       in
diff --git a/bytecomp/bytelink.mli b/bytecomp/bytelink.mli
index 9adf20fdcb..35a59df1bf 100644
--- a/bytecomp/bytelink.mli
+++ b/bytecomp/bytelink.mli
@@ -17,6 +17,9 @@ open Misc
 
 (* Link .cmo files and produce a bytecode executable. *)
 
+module Dep : Set.OrderedType with type t = modname * modname
+module DepSet : Set.S with type elt = Dep.t
+
 val link : filepath list -> filepath -> unit
 val reset : unit -> unit
 
@@ -35,7 +38,7 @@ type error =
   | Cannot_open_dll of filepath
   | Required_module_unavailable of modname * modname
   | Camlheader of string * filepath
-  | Wrong_link_order of (modname * modname) list
+  | Wrong_link_order of DepSet.t
   | Multiple_definition of modname * filepath * filepath
 
 exception Error of error
diff --git a/testsuite/tests/badly-ordered-deps/lib.ml b/testsuite/tests/badly-ordered-deps/lib.ml
new file mode 100644
index 0000000000..4b4431124e
--- /dev/null
+++ b/testsuite/tests/badly-ordered-deps/lib.ml
@@ -0,0 +1 @@
+let value = Main.value
diff --git a/testsuite/tests/badly-ordered-deps/main.bytecode.reference b/testsuite/tests/badly-ordered-deps/main.bytecode.reference
new file mode 100644
index 0000000000..8adfad056b
--- /dev/null
+++ b/testsuite/tests/badly-ordered-deps/main.bytecode.reference
@@ -0,0 +1,2 @@
+File "_none_", line 1:
+Error: Wrong link order: Lib depends on Main
diff --git a/testsuite/tests/badly-ordered-deps/main.ml b/testsuite/tests/badly-ordered-deps/main.ml
new file mode 100644
index 0000000000..ff4d1c90a1
--- /dev/null
+++ b/testsuite/tests/badly-ordered-deps/main.ml
@@ -0,0 +1,26 @@
+(* TEST
+
+(* Make sure ocamlc prints badly ordeered dependencies only once.
+   See issue #12074. We test with ocamlc.byte only. *)
+
+modules = "lib.ml"
+
+* setup-ocamlc.byte-build-env
+
+** ocamlc.byte
+all_modules = "main.ml"
+compile_only = "true"
+
+*** ocamlc.byte
+all_modules = "lib.ml"
+
+**** ocamlc.byte
+all_modules = "lib.cmo main.cmo"
+compile_only = "false"
+ocamlc_byte_exit_status = "2"
+
+***** check-ocamlc.byte-output
+
+*)
+
+let value = ()