&CORE::substr()

This commit makes &CORE::substr callable through references and via
&ampersand syntax.

It’s a bit awkward, as we need a substr op that is flagged as hav-
ing 4 arguments *and* possibly returning an lvalue.   The code in
op_lvalue_flags wasn’t really set up for that, so I needed to flag
the op with OPpMAYBE_LVSUB in coresub_op before it gets passed to
op_lvalue_flags.  It turned out that only that was necessary, as
op_lvalue_flags does an op_private == 4 check (rather than (op_private
& 7) == 4 or some such) when checking for the 4-arg case and croak-
ing.  When the op arrives in op_lvalue_flags, it’s already flagged
OPpMAYBE_LVSUB|4 which != 4.

pp_substr is also modified to check for nulls and, if necessary,
adjust its count of how many arguments were actually passed.)

1 files changed, 4 insertions, 2 deletions

diff --git a/gv.c b/gv.c
index 50ebea8e60..25548ebca3 100644
--- a/gv.c
+++ b/gv.c
@@ -1360,7 +1360,7 @@ Perl_gv_fetchpvn_flags(pTHX_ const char *nambeg, STRLEN full_len, I32 flags,
 	    case KEY_push:
 	    case KEY_setpgrp: case KEY_shift:
 	    case KEY_splice:
-	    case KEY_stat: case KEY_substr:
+	    case KEY_stat:
 	    case KEY_sysopen:
 	    case KEY_system:
 	    case KEY_tell: case KEY_tie: case KEY_tied:
@@ -1400,7 +1400,9 @@ Perl_gv_fetchpvn_flags(pTHX_ const char *nambeg, STRLEN full_len, I32 flags,
 	           new ATTRSUB. */
 	    (void)core_prototype((SV *)cv, name, code, &opnum);
 	    if (ampable) {
-		if (opnum == OP_VEC || opnum == OP_LOCK) CvLVALUE_on(cv);
+		if (opnum == OP_VEC || opnum == OP_LOCK
+		 || opnum == OP_SUBSTR)
+		    CvLVALUE_on(cv);
 		newATTRSUB(oldsavestack_ix,
 		           newSVOP(
 		                 OP_CONST, 0,