[perl #114942] Correct scoping for ‘for my $x(){} $x’

[perl #114942] Correct scoping for ‘for my $x(){} $x’

This was broken by commit 60ac52eb5d5.

What that commit did was to merge two different queues that the
lexer had for pending tokens.  Since bison requires that yylex
return exactly one token for each call, when the lexer sometimes has
to set aside tokens in a queue and return them from the next few
calls to yylex.

Formerly, there were two mechanism: the forced token queue (used by
force_next), and PL_pending_ident.  PL_pending_ident was used for
names that had to be looked up in the pads.

$foo was handled like this:

  First call to yylex:
    1. Put '$foo' in PL_tokenbuf.
    2. Set PL_pending_ident.
    3. Return a '$' token.
  Second call:
    PL_pending_ident is set, so call S_pending_ident, which looks up
    the name from PL_tokenbuf, and return the THING token containing
    the appropriate op.

The forced token queue took precedence over PL_pending_ident.  Chang-
ing the order (necessary for parsing ‘our sub foo($)’) caused some
XS::APItest tests to fail.  So I concluded that the two queues needed
to be merged.

As a result, the $foo handling changed to this:

  First call to yylex:
    1. Put '$foo' in PL_tokenbuf.
    2. Call force_ident_maybe_lex (S_pending_ident renamed and modi-
       fied), which looks up the symbol and adds it to the forced
       token queue.
    3. Return a '$' token.
  Second call:
    Return the token from the forced token queue.

That had the unforeseen consequence of changing this:

    for my $x (...) { ... }
    $x;

such that the $x was still visible after the for loop.  It only hap-
pened when the $ was the next token after the closing }:

$ ./miniperl -e 'for my $x(()){} $x = 3; warn $x'
Warning: something's wrong at -e line 1.
$ ./miniperl -e 'for my $x(()){} ;$x = 3; warn $x'
3 at -e line 1.

This broke Class::Declare.

The name lookup in the pad must not happen before the '$' token is
emitted.  At that point, the parser has not yet created the for loop
(which includes exiting its scope), as it does not yet know whether
there is a continue block.  (See the ‘FOR MY...’ branch of the
barestmt rule in perly.y.)  So we must delay the name lookup till the
second call.

So we rename force_ident_maybe_lex back to S_pending_ident, removing
the force_next stuff.  And we add a new force_ident_maybe_lex function
that adds a special ‘pending ident’ token to the forced token queue.

The part of yylex that handles pending tokens (case LEX_KNOWNEXT) is
modified to account for these special ‘pending ident’ tokens and call
S_pending_ident.