&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, 5 insertions, 1 deletions

diff --git a/op.c b/op.c
index 6d781baa95..50a61798ee 100644
--- a/op.c
+++ b/op.c
@@ -10397,7 +10397,11 @@ Perl_coresub_op(pTHX_ SV * const coreargssv, const int code,
 		argop->op_private |= OPpCOREARGS_DEREF2;
 	    if (scalar_mod_type(NULL, opnum))
 		argop->op_private |= OPpCOREARGS_SCALARMOD;
-	    goto onearg;
+	    if (opnum == OP_SUBSTR) {
+		o->op_private |= OPpMAYBE_LVSUB;
+		return o;
+	    }
+	    else goto onearg;
 	}
     }
 }