Add a new warning, "Newline in left-justified string for printf/sprintf"

to be issued if the string to be left-justified by s?printf contains
a newline.

Subject: [PATCH] RE: [perl #22599] Strange behaviour when combining foreac h and printf 
Message-ID: <533D273D4014D411AB1D00062938C4D904046571@hotel.npl.co.uk>

p4raw-id: //depot/perl@19752

1 files changed, 5 insertions, 0 deletions

diff --git a/sv.c b/sv.c
index 932438b862..d1324fc60f 100644
--- a/sv.c
+++ b/sv.c
@@ -9329,6 +9329,11 @@ Perl_sv_vcatpvfn(pTHX_ SV *sv, const char *pat, STRLEN patlen, va_list *args, SV
 	     p = SvEND(sv);
 	     *p = '\0';
 	}
+	if (left && ckWARN(WARN_PRINTF) && strchr(eptr, '\n') && 
+	    (PL_op->op_type == OP_PRTF || PL_op->op_type == OP_SPRINTF)) 
+	    Perl_warner(aTHX_ packWARN(WARN_PRINTF),
+		"Newline in left-justified string for %sprintf",
+			(PL_op->op_type == OP_PRTF) ? "" : "s");
 	
 	have = esignlen + zeros + elen;
 	need = (have > width ? have : width);