#show broken with -short-paths

[yallop]

This is a bug in 4.11.0+rc1:

$ ./install/bin/ocaml -short-paths
        OCaml version 4.11.0+dev16-2020-08-04

# type 'a t  = T;;
type 'a t = T
# #show t;;
>> Fatal error: Ident.rename t
Fatal error: exception Misc.Fatal_error

It was apparently introduced by #9086, specifically this change:

diff --git a/toplevel/topdirs.ml b/toplevel/topdirs.ml
index f4526692b6..78ab7eb51f 100644
--- a/toplevel/topdirs.ml
+++ b/toplevel/topdirs.ml
@@ -545,15 +545,66 @@ let () =
   reg_show_prim "show_type"
     (fun env loc id lid ->
        let _path, desc = Env.lookup_type ~loc lid env in
-       [ Sig_type (id, desc, Trec_not, Exported) ]
+       [ Sig_type (id, desc, Trec_first, Exported) ]
     )
     "Print the signature of the corresponding type constructor."

After this change, Printtyp.hide_rec_items attempts to rename persistent idents (i.e. Ident.Global values), which fails with the Misc.Fatal_error exception seen above.

I haven't investigated further, but I expect the easiest fix is to revert the single-line change above to restore the previous behaviour (i.e. printing type definitions with a bogus nonrec rather than exiting the interpreter with a fatal error).

[Octachron]

Yet another reason to switch to merlin's short path implementation. It is probably better to avoid a temporary regression on 4.11.0 indeed.

[yallop]

I expect the easiest fix is to revert the single-line change above to restore the previous behaviour

#9831 makes that change.