fix.pl6

    unless $dist.depends.first(/'panda' | 'Panda::'/)
        || $dist.build-depends.first(/'panda' | 'Panda::'/)
        || $dist.test-depends.first(/'panda' | 'Panda::'/) {

        my $legacy-fixer-code = q:to/END_LEGACY_FIX/;
            class Build {
                method isa($what) {
                    return True if $what.^name eq 'Panda::Builder';
                    callsame;
                }
            END_LEGACY_FIX

        my $legacy-code = $builder-path.IO.slurp;
        $legacy-code.subst-mutate(/'use Panda::' \w+ ';'/, '', :g);
        $legacy-code.subst-mutate('class Build is Panda::Builder {', "{$legacy-fixer-code}\n");
        $builder-path = "{$builder-path.absolute}.zef".IO;
        try { $builder-path.spurt($legacy-code) } || $builder-path.subst-mutate(/'.zef'$/, '');
    }