Make variable rename errors more consistent

Signed-off-by: Rudi Grinberg <rudi.grinberg@gmail.com>

src/super_context.ml

@@ -665,8 +665,8 @@ module Action = struct
       | Pair ("findlib", s) when syntax_version >= (1, 0) ->
         Loc.fail
           loc
-          "The findlib special variable is not supported anymore, please use lib instead:\n\
-           %%{lib:%s}"
+          "The findlib special variable is not supported in jbuild files, \
+           please use lib instead:\n%%{lib:%s} in dune files"
           s
       | Pair ("findlib", s)
       | Pair ("lib", s) -> begin
@@ -822,13 +822,14 @@ module Action = struct
           if syntax_version < (1, 0) then
             first_dep ()
           else
-            Loc.fail loc "Variable '<' is renamed to 'first-dep' in dune"
+            Loc.fail loc "Variable '<' is renamed to 'first-dep' in dune files"
         | "first-dep" when syntax_version >= (1, 0) -> first_dep ()
         | "^" ->
           if syntax_version < (1, 0) then
             Some (Value.L.paths deps_written_by_user)
           else
-            Loc.fail loc "Variable %%{^} has been renamed to %%{deps}"
+            Loc.fail loc
+              "Variable %%{^} has been renamed to %%{deps} in dune files"
         | "deps" when syntax_version >= (1, 0) ->
           Some (Value.L.paths deps_written_by_user)
         | _ -> None)
@@ -842,7 +843,8 @@ module Action = struct
       | [] -> ()
       | x :: _ ->
         let loc = String_with_vars.loc x in
-        Loc.warn loc "Aliases must not have targets, this target will be ignored.\n\
+        Loc.warn loc
+          "Aliases must not have targets, this target will be ignored.\n\
            This will become an error in the future.";
     end;
     let t, forms =

test/blackbox-tests/test-cases/findlib-error/run.t

@@ -3,8 +3,8 @@ We are dropping support for findlib in dune
   $ dune build --root in-dune target.txt
   Entering directory 'in-dune'
   File "dune", line 2, characters 25-37:
-  Error: The findlib special variable is not supported anymore, please use lib instead:
-  %{lib:pkg}
+  Error: The findlib special variable is not supported in jbuild files, please use lib instead:
+  %{lib:pkg} in dune files
   [1]
 
 But it must still be available in jbuild files