avoid side-effecting source held in scalar

Syntax plugins can modify the source being parsed.  It's fine for
them to modify the lexer buffer, but this must not be the same scalar
that was supplied to lex_start() and may be in use outside.  Therefore
always copy the scalar in lex_start() rather than just referencing it.
Fixes [perl #78358].

1 files changed, 1 insertions, 6 deletions

diff --git a/toke.c b/toke.c
index fa1882dcef..99aae57f3e 100644
--- a/toke.c
+++ b/toke.c
@@ -704,15 +704,10 @@ Perl_lex_start(pTHX_ SV *line, PerlIO *rsfp)
 
     if (!len) {
 	parser->linestr = newSVpvs("\n;");
-    } else if (SvREADONLY(line) || s[len-1] != ';' || !SvPOK(line)) {
-	/* avoid tie/overload weirdness */
+    } else {
 	parser->linestr = newSVpvn_flags(s, len, SvUTF8(line));
 	if (s[len-1] != ';')
 	    sv_catpvs(parser->linestr, "\n;");
-    } else {
-	SvTEMP_off(line);
-	SvREFCNT_inc_simple_void_NN(line);
-	parser->linestr = line;
     }
     parser->oldoldbufptr =
 	parser->oldbufptr =