s/.../$_++/ge assertion failure

The code that updated pos() on a match string assumed that it was SvPOK().
Cunning code like the following converted $_ to SvIOK only:

    $_ = 0;
    s/.?/$_++/ge;

1 files changed, 7 insertions, 1 deletions

diff --git a/pp_ctl.c b/pp_ctl.c
index c4f4d64616..335fb2101e 100644
--- a/pp_ctl.c
+++ b/pp_ctl.c
@@ -312,10 +312,16 @@ PP(pp_substcont)
 	SV * const sv
 	    = (pm->op_pmflags & PMf_NONDESTRUCT) ? cx->sb_dstr : cx->sb_targ;
 	MAGIC *mg;
+
+        /* the string being matched against may no longer be a string,
+         * e.g. $_=0; s/.../$_++/ge */
+
+        if (!SvPOK(sv))
+            SvPV_force_nomg_nolen(sv);
+
 	if (!(mg = mg_find_mglob(sv))) {
 	    mg = sv_magicext_mglob(sv);
 	}
-	assert(SvPOK(sv));
 	MgBYTEPOS_set(mg, sv, SvPVX(sv), m - orig);
     }
     if (old != rx)