toke.c:yylex: assert that PL_linestr is not a COW

and fix the one bug this uncovers.

With COW enabled all the time, it is easy to introduce bugs like this.
See also 4e917a04.  In short, toke.c expects to be able to modify
PL_linestr’s buffer.  Putting this assertion in yylex (a hot path)
will make sure PL_linestr never becomes a COW again.

diff --git a/toke.c b/toke.c
index 1615cb6..a8ce485 100644 (file)
--- a/toke.c
+++ b/toke.c
@@ -5145,6 +5145,8 @@ Perl_yylex(pTHX)
        return yylex();
     }
 
+    /* We really do *not* want PL_linestr ever becoming a COW. */
+    assert (!SvIsCOW(PL_linestr));
     s = PL_bufptr;
     PL_oldoldbufptr = PL_oldbufptr;
     PL_oldbufptr = s;
@@ -10536,8 +10538,49 @@ S_scan_str(pTHX_ char *start, int keep_quoted, int keep_delims, int re_reparse,
                int offset = s - SvPVX_const(PL_linestr);
                const bool found = sv_cat_decode(sv, PL_encoding, PL_linestr,
                                           &offset, (char*)termstr, termlen);
-               const char * const ns = SvPVX_const(PL_linestr) + offset;
-               char * const svlast = SvEND(sv) - 1;
+               const char *ns;
+               char *svlast;
+
+               if (SvIsCOW(PL_linestr)) {
+                   STRLEN bufend_pos, bufptr_pos, oldbufptr_pos;
+                   STRLEN oldoldbufptr_pos, linestart_pos, last_uni_pos;
+                   STRLEN last_lop_pos, re_eval_start_pos, s_pos;
+                   char *buf = SvPVX(PL_linestr);
+                   bufend_pos = PL_parser->bufend - buf;
+                   bufptr_pos = PL_parser->bufptr - buf;
+                   oldbufptr_pos = PL_parser->oldbufptr - buf;
+                   oldoldbufptr_pos = PL_parser->oldoldbufptr - buf;
+                   linestart_pos = PL_parser->linestart - buf;
+                   last_uni_pos = PL_parser->last_uni
+                       ? PL_parser->last_uni - buf
+                       : 0;
+                   last_lop_pos = PL_parser->last_lop
+                       ? PL_parser->last_lop - buf
+                       : 0;
+                   re_eval_start_pos =
+                       PL_parser->lex_shared->re_eval_start ?
+                            PL_parser->lex_shared->re_eval_start - buf : 0;
+                   s_pos = s - buf;
+
+                   sv_force_normal(PL_linestr);
+
+                   buf = SvPVX(PL_linestr);
+                   PL_parser->bufend = buf + bufend_pos;
+                   PL_parser->bufptr = buf + bufptr_pos;
+                   PL_parser->oldbufptr = buf + oldbufptr_pos;
+                   PL_parser->oldoldbufptr = buf + oldoldbufptr_pos;
+                   PL_parser->linestart = buf + linestart_pos;
+                   if (PL_parser->last_uni)
+                       PL_parser->last_uni = buf + last_uni_pos;
+                   if (PL_parser->last_lop)
+                       PL_parser->last_lop = buf + last_lop_pos;
+                   if (PL_parser->lex_shared->re_eval_start)
+                       PL_parser->lex_shared->re_eval_start  =
+                           buf + re_eval_start_pos;
+                   s = buf + s_pos;
+               }
+               ns = SvPVX_const(PL_linestr) + offset;
+               svlast = SvEND(sv) - 1;
 
                for (; s < ns; s++) {
                    if (*s == '\n' && !PL_rsfp && !PL_parser->filtered)