sub MY::postamble {
  return '' if !-e '.git';
  my $container = 'graphqlperl/graphql';
  my $prereq = "${container}-prereq";
  <<EOF;
\$(VERSION_FROM) : graphql.pgx
\t\$(PERL) -Ilib -MGraphQL::Language::Grammar=compile

pure_all :: README.md

README.md : \$(VERSION_FROM)
\tpod2markdown \$< >\$\@
# then some Docker stuff

##</code><code>##

sub coretarget {
    my ($self) = @_;
    # remember the fundamental ones end up far to right as much deps on them
    # a "right" is either scalar (named target) or tuple of
    #     [ \@dir, \@targets, \@prereqs ]
    # @dir is dir parts for use by File::Spec
    # @targets is make targets within that dir
    # @prereqs are named targets - undef=[]
    # all a left's rights are made concurrently, no sequence - list ALL prereqs
    my @left2rights = (
        [
            coregen => [
                [ [ qw(Basic) ], [ qw(pm_to_blib) ], ],
                [ [ qw(Basic Core) ], [ qw(pm_to_blib) ], ],
                [ [ qw(Basic Gen) ], [ qw(all) ], ],
            ]
        ],
        [
            core => [
                [ [ qw(Basic SourceFilter) ], [ qw(pm_to_blib) ], ],
                map [
                    [ 'Basic', $_ ],
                    [ qw(pm_to_blib dynamic) ],
                    [ 'coregen' ],
                # the modules in PDL::LiteF, used in t/core.t
                ], qw(Core Ops Primitive Ufunc Slices Bad Math MatrixOps),
            ]
        ],
        [
            basic => [
                map [
                    $_,
                    [ qw(pm_to_blib dynamic) ],
                    [ 'core' ],
                ], @basics,
            ]
        ],
        [
            basictest => [
                map [
                    $_,
                    [ 'test' ],
                    [ 'basic' ],
                ], @basics,
            ]
        ],
    );
    join "\n", map flatten_parallel_target($self, $_), @left2rights;
}

sub format_chunk {
    my ($self, $left, $deps, $dir, $targets) = @_;
    my @m = join ' ', $left, ':', @{$deps||[]};
    my $fsdir = File::Spec->catdir(@$dir);
    push @m, "\t" . $self->oneliner(
        "die \$! unless chdir q($fsdir); exec q(\$(MAKE) @$targets)"
    );
    join '', map "$_\n", @m;
}

# output: list of make chunks with target, deps, recipes
sub flatten_parallel_target {
    my ($self, $left2rights) = @_;
    my ($left, $rights) = @$left2rights;
    my (@deps, @recipes, @otherchunks);
    for my $right (@$rights) {
        if (ref $right) {
            #     [ \@dir, \@targets, \@prereqs ]
            # @dir is dir parts for use by File::Spec
            # @targets is make targets within that dir
            # @prereqs are named targets - undef=[]
            my ($dir, $targets, $prereqs) = @$right;
            my $target_name = parallel_target_mangle($self, $dir, $targets);
            push @deps, $target_name;
            push @otherchunks, format_chunk(
                $self, $target_name, $prereqs, $dir, $targets
            );
        } else {
            push @deps, $right;
        }
    }
    (
        join(' : ', $left, join ' ', @deps) . "\n",
        @otherchunks,
    );
}

sub parallel_target_mangle {
    my ($self, $dir, $targets) = @_;
    my $target = join '_', @$dir, @$targets;
    $target =~ s#[/\\]#_#g; # avoid ambiguity with filenames
    $target;
}