Stop delete local $ENV{foo} from leaking

It was only leaking when the env var did not already exist.

The code in question in pp.c:S_do_delete_local was calling hv_delete
to delete the element, which autovivifies, deletes, and returns a mag-
ical mortal for magical hashes.  It was assuming that if a value was
returned the element must have existed, so it was calling SvREFCNT_inc
on the returned mortal to de-mortalize it (since it has to be
restored).  Whether the element had existed previously was already
recorded in a bool named ‘preeminent’ (strange name).  This variable
should be checked before the SvREFCNT_inc.

I found the same bug in the array code path, potentially affecting
@- and @+, so I fixed it.  But I didn’t write a test, as that would
involve a custom regexp engine.

1 files changed, 4 insertions, 2 deletions

diff --git a/pp.c b/pp.c
index ea7b4c2691..3eb3cea6af 100644
--- a/pp.c
+++ b/pp.c
@@ -4511,7 +4511,8 @@ S_do_delete_local(pTHX)
 		}
 		else {
 		    sv = hv_delete_ent(hv, keysv, 0, 0);
-		    SvREFCNT_inc_simple_void(sv); /* De-mortalize */
+		    if (preeminent)
+			SvREFCNT_inc_simple_void(sv); /* De-mortalize */
 		}
 		if (preeminent) {
 		    if (!sv) DIE(aTHX_ PL_no_helem_sv, SVfARG(keysv));
@@ -4546,7 +4547,8 @@ S_do_delete_local(pTHX)
 		    }
 		    else {
 			sv = av_delete(av, idx, 0);
-		        SvREFCNT_inc_simple_void(sv); /* De-mortalize */
+			if (preeminent)
+			   SvREFCNT_inc_simple_void(sv); /* De-mortalize */
 		    }
 		    if (preeminent) {
 		        save_aelem_flags(av, idx, &sv, SAVEf_KEEPOLDELEM);