[Super errors] Better msg for Str

jscomp/super_errors/super_typetexp.ml

@@ -139,17 +139,33 @@ let report_error env ppf = function
       spellcheck ppf Env.fold_values env lid;
   | Unbound_module lid ->
       (* modified *)
-      fprintf ppf "@[<v>\
-          @{<info>The module or file %a can't be found.@}@,@,\
-          @[<v 2>- If it's a third-party dependency:@,\
-            - Did you list it in bsconfig.json?@,\
-            - @[Did you run `bsb` instead of `bsb -make-world`@ (latter builds third-parties)@]?\
-          @]@,\
-          - Did you include the file's directory in bsconfig.json?@]\
-        @]"
-        longident lid;
+      begin match lid with
+      | Lident "Str" -> 
+        begin
+          fprintf ppf "@[\
+              @{<info>The module or file %a can't be found.@}@,@,\
+              Are you trying to use the standard library's Str?@ \
+              If you're compiling to JavaScript,@ use @{<info>Js.Re@} instead.@ \
+              Otherwise, add str.cma to your ocamlc/ocamlopt command.\
+            @]"
+            longident lid 
+        end
+      | lid -> 
+        begin
+          fprintf ppf "@[<v>\
+              @{<info>The module or file %a can't be found.@}@,\
+              @[<v 2>- If it's a third-party dependency:@,\
+                - Did you list it in bsconfig.json?@,\
+                - @[Did you run `bsb` instead of `bsb -make-world`@ (latter builds third-parties)@]?\
+              @]@,\
+              - Did you include the file's directory in bsconfig.json?@]\
+            @]"
+            longident lid
+        end
+      end;
       spellcheck ppf Env.fold_modules env lid
   | Unbound_constructor lid ->
+      (* modified *)
       fprintf ppf "@[<v>\
       @{<info>The variant constructor %a can't be found.@}@,@,\
       @[<v 2>- If it's defined in another module or file, bring it into scope by:@,\
@@ -162,6 +178,7 @@ let report_error env ppf = function
       Typetexp.spellcheck_simple ppf Env.fold_constructors (fun d -> d.cstr_name)
         env lid;
   | Unbound_label lid ->
+      (* modified *)
       fprintf ppf "@[<v>\
       @{<info>The record field %a can't be found.@}@,@,\
       If it's defined in another module or file, bring it into scope by:@,\