Protect ${^E_NCODING} from abuse

When read, it is now always undef.  When set, it croaks as though
read-only except in the encoding package.  Hopefully that will dis-
suade anyone from depending on it.

1 files changed, 4 insertions, 0 deletions

diff --git a/mg.c b/mg.c
index f4ee820b93..653800347a 100644
--- a/mg.c
+++ b/mg.c
@@ -858,6 +858,8 @@ Perl_magic_get(pTHX_ SV *sv, MAGIC *mg)
 	 if (nextchar != '\0') {
             if (strEQ(remaining, "NCODING"))
                 sv_setsv(sv, _get_encoding());
+            else if (strEQ(remaining, "_NCODING"))
+                sv_setsv(sv, NULL);
             break;
         }
 
@@ -2648,6 +2650,8 @@ Perl_magic_set(pTHX_ SV *sv, MAGIC *mg)
             /* It may be the shadow variable ${E_NCODING} which has lexical
              * scope.  See comments at Perl__get_encoding in this file */
             if (*(mg->mg_ptr + 1) == '_') {
+                if (CopSTASH(PL_curcop) != get_hv("encoding::",0))
+                    Perl_croak_no_modify();
                 lex = TRUE;
                 offset++;
             }