Merge pull request #584 from rgrinberg/improve-error-modules

Improve error in modules partition

src/modules_partitioner.ml

@@ -37,7 +37,14 @@ let emit_warnings t =
       Loc.warn loc
         "Module %S is used in several stanzas:@\n\
          @[<v>%a@]@\n\
-         This will become an error in the future."
+         @[%a@]@\n\
+         This warning will become an error in the future."
         name
         (Fmt.list (Fmt.prefix (Fmt.string "- ") Loc.pp_file_colon_line))
-        locs)
+        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.")

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

@@ -3,7 +3,11 @@
   Warning: Module "Lib" is used in several stanzas:
   - jbuild:8
   - jbuild:4
-  This will become an error in the future.
+  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.
   Multiple rules generated for _build/default/lib.o:
   - <internal location>
   - <internal location>
@@ -14,7 +18,11 @@
   Warning: Module "X" is used in several stanzas:
   - src/jbuild:4
   - src/jbuild:3
-  This will become an error in the future.
+  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 src/x.ml.d
         ocamlc src/.a.objs/a.{cmi,cmo,cmt}
         ocamlc src/.a.objs/a__X.{cmi,cmo,cmt}