From: Dave Mitchell <davem@fdisolutions.com>
Date: Wed, 25 Feb 2004 17:10:56 +0000 (+0000)
Subject: stop "const in void context" warning for a const in an
X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=commitdiff_plain;h=e7fec78e344a7fdea63b9a2551a3c57cc1a50f4d;p=p5sagit%2Fp5-mst-13.2.git

stop "const in void context" warning for a const in an
optimised-away boolean expresssion, eg 5 || print;

p4raw-id: //depot/perl@22376
---

diff --git a/op.c b/op.c
index 4bd252c..4273e65 100644
--- a/op.c
+++ b/op.c
@@ -677,10 +677,14 @@ Perl_scalarvoid(pTHX_ OP *o)
 	else {
 	    if (ckWARN(WARN_VOID)) {
 		useless = "a constant";
+		/* don't warn on optimised away booleans, eg 
+		 * use constant F, 5; Foo || print; */
+		if (cSVOPo->op_private & OPpCONST_SHORTCIRCUIT)
+		    useless = 0;
 		/* the constants 0 and 1 are permitted as they are
 		   conventionally used as dummies in constructs like
 		        1 while some_condition_with_side_effects;  */
-		if (SvNIOK(sv) && (SvNV(sv) == 0.0 || SvNV(sv) == 1.0))
+		else if (SvNIOK(sv) && (SvNV(sv) == 0.0 || SvNV(sv) == 1.0))
 		    useless = 0;
 		else if (SvPOK(sv)) {
                   /* perl4's way of mixing documentation and code
@@ -3363,11 +3367,13 @@ S_new_logop(pTHX_ I32 type, I32 flags, OP** firstp, OP** otherp)
 	if ((type == OP_AND) == (SvTRUE(((SVOP*)first)->op_sv))) {
 	    op_free(first);
 	    *firstp = Nullop;
+	    other->op_private |= OPpCONST_SHORTCIRCUIT;
 	    return other;
 	}
 	else {
 	    op_free(other);
 	    *otherp = Nullop;
+	    first->op_private |= OPpCONST_SHORTCIRCUIT;
 	    return first;
 	}
     }
diff --git a/op.h b/op.h
index 889b3ea..116bcd3 100644
--- a/op.h
+++ b/op.h
@@ -181,6 +181,7 @@ Deprecated.  Use C<GIMME_V> instead.
 #define OPpTARGET_MY		16	/* Target is PADMY. */
 
 /* Private for OP_CONST */
+#define	OPpCONST_SHORTCIRCUIT	4	/* eg the constant 5 in (5 || foo) */
 #define	OPpCONST_STRICT		8	/* bearword subject to strict 'subs' */
 #define OPpCONST_ENTERED	16	/* Has been entered as symbol. */
 #define OPpCONST_ARYBASE	32	/* Was a $[ translated to constant. */
diff --git a/t/lib/warnings/op b/t/lib/warnings/op
index c101ffe..3aa5299 100644
--- a/t/lib/warnings/op
+++ b/t/lib/warnings/op
@@ -525,6 +525,9 @@ Useless use of a variable in void context at - line 6.
 use warnings 'void' ;
 "abc"; # OP_CONST
 7 ; # OP_CONST
+5 || print "bad\n";	# test OPpCONST_SHORTCIRCUIT
+use constant U => undef;
+print "boo\n" if U;	# test OPpCONST_SHORTCIRCUIT
 no warnings 'void' ;
 "abc"; # OP_CONST
 7 ; # OP_CONST