Turn warning about modules being used multiple times into errors

Signed-off-by: Jeremie Dimino <jeremie@dimino.org>

src/gen_rules.ml

@@ -960,7 +960,7 @@ module Gen(P : Install_rules.Params) = struct
     (* This interprets "rule" and "copy_files" stanzas. *)
     let files = text_files ~dir:ctx_dir in
     let all_modules = modules_by_dir ~dir:ctx_dir in
-    let modules_partitioner = Modules_partitioner.create () in
+    let modules_partitioner = Modules_partitioner.create ~dir_kind:kind in
     let merlins =
       List.filter_map stanzas ~f:(fun stanza ->
         let dir = ctx_dir in
@@ -1008,7 +1008,7 @@ module Gen(P : Install_rules.Params) = struct
         in
         Menhir_rules.gen_rules cctx m
       | _ -> ());
-    Modules_partitioner.emit_warnings modules_partitioner
+    Modules_partitioner.emit_errors modules_partitioner
 
      let gen_rules ~dir components : Build_system.extra_sub_directories_to_keep =
     (match components with

src/modules_partitioner.ml

@@ -1,11 +1,13 @@
 open Import
 
 type 'a t =
-  { mutable used : ('a * Loc.t list) Module.Name.Map.t
+  { dir_kind     : File_tree.Dune_file.Kind.t
+  ; mutable used : ('a * Loc.t list) Module.Name.Map.t
   }
 
-let create () =
-  { used = Module.Name.Map.empty
+let create ~dir_kind =
+  { dir_kind
+  ; used = Module.Name.Map.empty
   }
 
 let acknowledge t part ~loc ~modules =
@@ -28,23 +30,39 @@ let acknowledge t part ~loc ~modules =
 
 let find t name = Option.map (Module.Name.Map.find t.used name) ~f:fst
 
-let emit_warnings t =
+let emit_errors t =
   Module.Name.Map.iteri t.used ~f:(fun name (_, locs) ->
     match locs with
     | [] | [_] -> ()
     | loc :: _ ->
       let loc = Loc.in_file loc.start.pos_fname in
-      Loc.warn loc
-        "Module %a is used in several stanzas:@\n\
-         @[<v>%a@]@\n\
-         @[%a@]@\n\
-         This warning will become an error in the future."
-        Module.Name.pp_quote name
-        (Fmt.list (Fmt.prefix (Fmt.string "- ") Loc.pp_file_colon_line))
-        locs
-        Format.pp_print_text
-        "To remove this warning, you must specify an explicit \"modules\" \
-         field in every library, executable, and executables stanzas in \
-         this jbuild file. Note that each module cannot appear in more \
-         than one \"modules\" field - it must belong to a single library \
-         or executable.")
+      match t.dir_kind with
+      | Jbuild ->
+        Loc.warn loc
+          "Module %a is used in several stanzas:@\n\
+           @[<v>%a@]@\n\
+           @[%a@]@\n\
+           This warning will become an error in the future."
+          Module.Name.pp_quote name
+          (Fmt.list (Fmt.prefix (Fmt.string "- ") Loc.pp_file_colon_line))
+          locs
+          Format.pp_print_text
+          "To remove this warning, you must specify an explicit \"modules\" \
+           field in every library, executable, and executables stanzas in \
+           this jbuild file. Note that each module cannot appear in more \
+           than one \"modules\" field - it must belong to a single library \
+           or executable."
+      | Dune ->
+        Loc.fail loc
+          "Module %a is used in several stanzas:@\n\
+           @[<v>%a@]@\n\
+           @[%a@]"
+          Module.Name.pp_quote name
+          (Fmt.list (Fmt.prefix (Fmt.string "- ") Loc.pp_file_colon_line))
+          locs
+          Format.pp_print_text
+          "To fix this error, you must specify an explicit \"modules\" \
+           field in every library, executable, and executables stanzas in \
+           this dune file. Note that each module cannot appear in more \
+           than one \"modules\" field - it must belong to a single library \
+           or executable.")

src/modules_partitioner.mli

@@ -4,7 +4,7 @@ open! Stdune
 
 type 'a t
 
-val create : unit -> 'a t
+val create : dir_kind:File_tree.Dune_file.Kind.t -> 'a t
 
 (** [acknowledge t partition ~loc ~modules] registers the fact that [modules]
     are associated with [loc].
@@ -22,6 +22,6 @@ val acknowledge
 (** Find which partition a module is part of *)
 val find : 'a t -> Module.Name.t -> 'a option
 
-(** To be called after processing a directory. Emit warnings about
-    detected problems *)
-val emit_warnings : _ t -> unit
+(** To be called after processing a directory. Emit errors or warnings
+    about detected problems *)
+val emit_errors : _ t -> unit

test/blackbox-tests/test-cases/ocamldep-multi-stanzas/jbuild/jbuild

@@ -0,0 +1,7 @@
+(library
+ ((name lib)
+  (modules (:standard \ test))))
+
+(executable
+ ((name test)
+  (libraries (lib))))

test/blackbox-tests/test-cases/ocamldep-multi-stanzas/jbuild/lib.ml

@@ -0,0 +1 @@
+let run () = print_endline "foo bar"

test/blackbox-tests/test-cases/ocamldep-multi-stanzas/jbuild/src/jbuild

@@ -0,0 +1,2 @@
+(library ((name a)))
+(library ((name b)))

test/blackbox-tests/test-cases/ocamldep-multi-stanzas/jbuild/src/x.ml

@@ -0,0 +1 @@
+let x = 42

test/blackbox-tests/test-cases/ocamldep-multi-stanzas/jbuild/test.ml

@@ -0,0 +1 @@
+Lib.run ();;

test/blackbox-tests/test-cases/ocamldep-multi-stanzas/run.t

@@ -1,30 +1,25 @@
-  $ dune exec ./test.exe --debug-dep --display short
-  File "dune", line 1, characters 0-0:
+  $ dune exec ./test.exe --debug-dep --display short --root jbuild
+  Entering directory 'jbuild'
+  File "jbuild", line 1, characters 0-0:
   Warning: Module "Lib" is used in several stanzas:
-  - dune:6
-  - dune:2
+  - jbuild:6
+  - jbuild:2
   To remove this warning, you must specify an explicit "modules" field in every
   library, executable, and executables stanzas in this jbuild file. Note that
   each module cannot appear in more than one "modules" field - it must belong
   to a single library or executable.
   This warning will become an error in the future.
-      ocamldep lib.ml.d
-        ocamlc .lib.objs/lib.{cmi,cmo,cmt}
-      ocamlopt .lib.objs/lib.{cmx,o}
-      ocamlopt lib.{a,cmxa}
-      ocamldep test.ml.d
-        ocamlc .test.eobjs/lib.{cmi,cmo,cmt}
-      ocamlopt .test.eobjs/lib.{cmx,o}
-        ocamlc .test.eobjs/test.{cmi,cmo,cmt}
-      ocamlopt .test.eobjs/test.{cmx,o}
-      ocamlopt test.exe
-  foo bar
+  Multiple rules generated for _build/default/lib$ext_obj:
+  - <internal location>
+  - <internal location>
+  [1]
 
-  $ dune build src/a.cma --debug-dep --display short
-  File "src/dune", line 1, characters 0-0:
+  $ dune build src/a.cma --debug-dep --display short --root jbuild
+  Entering directory 'jbuild'
+  File "src/jbuild", line 1, characters 0-0:
   Warning: Module "X" is used in several stanzas:
-  - src/dune:2
-  - src/dune:1
+  - src/jbuild:2
+  - src/jbuild:1
   To remove this warning, you must specify an explicit "modules" field in every
   library, executable, and executables stanzas in this jbuild file. Note that
   each module cannot appear in more than one "modules" field - it must belong
@@ -34,3 +29,27 @@
         ocamlc src/.a.objs/a.{cmi,cmo,cmt}
         ocamlc src/.a.objs/a__X.{cmi,cmo,cmt}
         ocamlc src/a.cma
+
+  $ dune exec ./test.exe --debug-dep --display short --root dune
+  Entering directory 'dune'
+  File "dune", line 1, characters 0-0:
+  Error: Module "Lib" is used in several stanzas:
+  - dune:6
+  - dune:2
+  To fix this error, you must specify an explicit "modules" field in every
+  library, executable, and executables stanzas in this dune file. Note that
+  each module cannot appear in more than one "modules" field - it must belong
+  to a single library or executable.
+  [1]
+
+  $ dune build src/a.cma --debug-dep --display short --root dune
+  Entering directory 'dune'
+  File "src/dune", line 1, characters 0-0:
+  Error: Module "X" is used in several stanzas:
+  - src/dune:2
+  - src/dune:1
+  To fix this error, you must specify an explicit "modules" field in every
+  library, executable, and executables stanzas in this dune file. Note that
+  each module cannot appear in more than one "modules" field - it must belong
+  to a single library or executable.
+  [1]