Bug introduced in V10.4 or earlier and persisting through V11.3


SystemOpen @ Export[
  FileNameJoin[{$TemporaryDirectory, "test.m" }]
, "x = \"
    (* ::Chapter:: *)
    (* Metadata*)
, "Text"

enter image description here

Well, I didn't expect this. It wasn't how I faced it, I just had a string template for a package inside a package and when I reopened the file it was corrupted.

Is this expected? Shouldn't expressions have priority over package tokens. The more that it is hard to find any documentation about (* ::Section:: *) and friends.

What practices should I follow to not be hit by this again?

  • 2
    $\begingroup$ Wow now that is a nasty bug. WRI's package parse is already pretty slow. Good to know it's somewhat unreliable too! $\endgroup$ – b3m2a1 May 24 '18 at 20:18
  • $\begingroup$ @b3m2a1 I just noticed it is even worse, I assumed it only happens when the line starts with the token, but even whatever code "(* ::Chapter:: *)" will break it :P $\endgroup$ – Kuba May 25 '18 at 7:35
  • $\begingroup$ Would it be acceptable to escape the special tag as \(* or (\*? I think they must get prior treatment before standard parsing. $\endgroup$ – Silvia Jun 2 '18 at 16:02
  • $\begingroup$ @Silvia I will try later but it depends how much hassle it would be to use it and what implications it would have, e.g. I want to Export["test.m", x, "Text"] and it should open as a valid package with chapter correctly parsed as a real token. $\endgroup$ – Kuba Jun 4 '18 at 13:00

Maybe you can try this, bearing in mind that Mathematica is really a bootstrapping system, i.e., it can fix itself (except Dynamic, that seems pretty unfixable)

file = FileNameJoin[{$TemporaryDirectory, "test.m"}];
  "x = \"
      (* ::Chapter:: *)
      (* Metadata*)
    \"", "Text"];
bin = Import[file, "Text"];
Export[file, "", "Text"];
NotebookWrite[nb = NotebookOpen[file], ExportString[bin, "Text"]];
FrontEndExecute[FrontEndToken[nb, "Save"]]

enter image description here

  • 1
    $\begingroup$ 1) next time you open the file the issue persists so it would have to be a default action to open .m files 2) which can't be enforced if you just double click on a .m file from e.g. desktop. $\endgroup$ – Kuba May 24 '18 at 20:12

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