perldiag: \%d better written as $%d

splain can’t necessarily find it if we hard-code the number:

$ ./perl -Ilib -Mdiagnostics -we '()="" =~ s/()()/\1/r'
\1 better written as $1 at -e line 1 (#1)
    (W syntax) Outside of patterns, backreferences live on as variables.
    The use of backslashes is grandfathered on the right-hand side of a
    substitution, but stylistically it's better to use the variable form
    because other Perl programmers will expect it, and it works better if
    there are more than 9 backreferences.

$ ./perl -Ilib -Mdiagnostics -we '()="" =~ s/()()/\2/r'
\2 better written as $2 at -e line 1.
$

%d is more intuitive than %c here, so I used %d in the pod instead of
copying the C code that generates it.

1 files changed, 1 insertions, 0 deletions

diff --git a/toke.c b/toke.c
index cd653dd3e5..efb6533ed8 100644
--- a/toke.c
+++ b/toke.c
@@ -3379,6 +3379,7 @@ S_scan_const(pTHX_ char *start)
 	    if (PL_lex_inwhat == OP_SUBST && !PL_lex_inpat &&
 		isDIGIT(*s) && *s != '0' && !isDIGIT(s[1]))
 	    {
+		/* diag_listed_as: \%d better written as $%d */
 		Perl_ck_warner(aTHX_ packWARN(WARN_SYNTAX), "\\%c better written as $%c", *s, *s);
 		*--s = '$';
 		break;