Deprecate use of := to mean an empty attribute list in my $pi := 4;

An accident of Perl's parser meant that my $pi := 4; was parsed as an empty
attribute list. Empty attribute lists are ignored, hence the above is
equivalent to my $pi = 4; However, the fact that it is currently valid syntax
means that := cannot be used as new token, without silently changing the
meaning of existing code.

Hence it is now deprecated, so that it can subsequently be removed, allowing
the possibility of := to be used as a new token with new semantics.

1 files changed, 3 insertions, 0 deletions

diff --git a/toke.c b/toke.c
index bd20434753..fa78415331 100644
--- a/toke.c
+++ b/toke.c
@@ -4298,6 +4298,9 @@ Perl_yylex(pTHX)
 	    if (!PL_in_my || PL_lex_state != LEX_NORMAL)
 		break;
 	    PL_bufptr = s;	/* update in case we back off */
+	    if (*s == '=') {
+		deprecate(":= for an empty attribute list");
+	    }
 	    goto grabattrs;
 	case XATTRBLOCK:
 	    PL_expect = XBLOCK;