sub signatures: use parser rather than lexer

Currently the signature of a sub (i.e. the '($a, $b = 1)' bit) is parsed
in toke.c using a roll-your-own mini-parser. This commit makes
the signature be part of the general grammar in perly.y instead.

In theory it should still generate the same optree as before, except
that an OP_STUB is no longer appended to each signature optree: it's
unnecessary, and I assume that was a hangover from early development of
the original signature code.

Error messages have changed somewhat: the generic 'Parse error' has
changed to the generic 'syntax error', with the addition of ', near "xyz"'
now appended to each message.

Also, some specific error messages have been added; for example
(@a=1) now says that slurpy params can't have a default vale, rather than
just giving 'Parse error'.

It introduces a new lexer expect state, XSIGVAR, since otherwise when
the lexer saw something like '($, ...)' it would see the identifier
'$,' rather than the tokens '$' and ','.

Since it no longer uses parse_termexpr(), it is no longer subject to the
bug (#123010) associated with that; so sub f($x = print, $y) {}
is no longer mis-interpreted as sub f($x = print($_, $y)) {}

1 files changed, 3 insertions, 2 deletions

diff --git a/sv.c b/sv.c
index c77a8bb570..7459d7061d 100644
--- a/sv.c
+++ b/sv.c
@@ -12981,8 +12981,9 @@ Perl_parser_dup(pTHX_ const yy_parser *const proto, CLONE_PARAMS *const param)
     parser->in_my	= proto->in_my;
     parser->in_my_stash	= hv_dup(proto->in_my_stash, param);
     parser->error_count	= proto->error_count;
-
-
+    parser->sig_elems	= proto->sig_elems;
+    parser->sig_optelems= proto->sig_optelems;
+    parser->sig_slurpy  = proto->sig_slurpy;
     parser->linestr	= sv_dup_inc(proto->linestr, param);
 
     {