[perl #54444] [rakudo] 'No such caller depth' with pure perl mod_perl6

[via RT]

# New Ticket Created by  Jeff Horwitz 
# Please include the string:  [perl #54444]
# in the subject line of all future correspondence about this issue. 
# <URL: http://rt.perl.org/rt3/Ticket/Display.html?id=54444 >


while converting mod_perl6 from PIR to pure perl6, i encountered the 
following error when running a handler:

   No such caller depth
   current instr.: 'parrot;ModParrot;HLL;perl6;handler' pc 62 (EVAL_13:46)

i tracked down the error to this block in perl6's actions.pm:

         unless $?BLOCK.symbol('$/') {
             $init.push( PAST::Var.new( :name('$/'), :isdecl(1) ) );
             $?BLOCK.symbol( '$/', :scope('lexical') );
             $init.push(
                 PAST::Op.new(
                     :inline(
                           "    %r = getinterp\n"
                         ~ "    %r = %r['lexpad';1]\n"
                         ~ "    if null %r goto no_match_to_copy\n"
                         ~ "    %r = %r['$/']\n"
                         ~ "    store_lex '$/', %r\n"
                         ~ "  no_match_to_copy:\n"
                     )
                 )
             );
         }

this code assumes there is a previous call frame which might contain a 
lexpad, which is always true when called from PIR or the PCT command line. 
however, in a pure perl mod_perl6, a perl6 sub is called directly from C, 
and therefore lives in the top level call frame.  any reference to the 
nonexistent previous frame using the interpreter object bombs out.

you can reproduce this problem in pure PIR with this:

     .sub main :main
         $P0 = getinterp
         $P1 = $P0['lexpad';1]
     .end

if we want perl6 subs to be directly invokable from an embedded 
environemnt, we either need to teach perl6 to be smarter about this or 
change how parrot handles this kind of exception.

-jeff