code-partial.p6

    sub hunt_loose_adverbs_in_arglist($/, @past) {
        # if we have a non-comma-separated list of adverbial pairs in an
        # arglist or semiarglist, only the first will be passed as a named
        # argument.

        # Thus, we need to find chained adverbs. They show up on the parse
        # tree as colonpair rules followed by a fake_infix.

        # if nqp::getenvhash<COLONPAIR> eq 'trace' { say($/.dump) }
        nqp::atkey(nqp::getenvhash(),'ZZ') && nqp::say('ZZ1: ' ~ $/.dump);
        
        if +$/.list == 1 && nqp::istype($/[0].ast, QAST::Op) && $/[0].ast.op eq 'call' && $/[0].ast.name ne 'infix:<,>' {
            nqp::die("these adverbs belong to a deeper-nested thing");
        }
        if $<fake_infix>
               || $<colonpair> && +($/.list) == 0 && +($/.hash) == 1 {
            nqp::atkey(nqp::getenvhash(),'ZZ2') && nqp::say('ZZ2.1');
            if +($/.list) == 1 {
                nqp::atkey(nqp::getenvhash(),'ZZ2') && nqp::say('ZZ2.2');
                hunt_loose_adverbs_in_arglist($/[0], @past);
            }
            my $Pair := $*W.find_symbol(['Pair']);
            if $<colonpair> && istype($<colonpair>.ast.returns, $Pair) {
                nqp::atkey(nqp::getenvhash(),'ZZ2') && nqp::say('ZZ2.3' ~ $<colonpair>.dump);
                nqp::atkey(nqp::getenvhash(),'ZZ2') && nqp::say('ZZ2.3' ~ $<colonpair>.ast.dump);
                if $*WAS_SKIPPED {
                    nqp::atkey(nqp::getenvhash(),'ZZ2') && nqp::say('ZZ2.4');
                    nqp::push(@past, $<colonpair>.ast);
                } else {
                    nqp::atkey(nqp::getenvhash(),'ZZ2') && nqp::say('ZZ2.5');
                    $*WAS_SKIPPED := 1;
                }
            }
        } elsif $<OPER>.Str eq ',' {
            nqp::atkey(nqp::getenvhash(),'ZZ2') && nqp::say('ZZ2.6');
            my $*WAS_SKIPPED := 0;
            for $/.list {
                nqp::atkey(nqp::getenvhash(),'ZZ2') && nqp::say('ZZ2.7');
                hunt_loose_adverbs_in_arglist($_, @past);
            }
        }
    }

output.txt

ZZ1: - 0: :w
  - colonpair: :w
    - identifier: w
- fake_infix: 
  - O: 
- OPER: 
  - O: 
- colonpair: :h<1>
  - coloncircumfix: <1>
    - circumfix: <1>
      - nibble: 1
  - identifier: h

ZZ2.1
ZZ2.2
ZZ1: - colonpair: :w
  - identifier: w

ZZ2.1
ZZ2.3- identifier: w

ZZ2.3- QAST::Op(callmethod new) <wanted nosink> :statement_id<2> :w
  - QAST::Var(lexical Pair) <wanted> :w
  - QAST::Want <wanted>
    - QAST::WVal(Str) 
    - Ss
    - QAST::SVal(w) 
  - QAST::Op(p6bool) <wanted>
    - QAST::IVal(1) 
  - QAST::WVal+{QAST::SpecialArg}(IntStr :named<h>) <wanted> 1

ZZ2.5
ZZ2.3- coloncircumfix: <1>
  - circumfix: <1>
    - nibble: 1
- identifier: h

ZZ2.3- QAST::Op(callmethod new) <nosink> :h<1>
  - QAST::Var(lexical Pair) <wanted> :h<1>
  - QAST::Want 
    - QAST::WVal(Str) 
    - Ss
    - QAST::SVal(h) 
  - QAST::WVal+{QAST::SpecialArg}(:named<h>) <wanted> 1

ZZ2.4
===SORRY!===
Unknown QAST node type NQPMu