@veprbl, thanks for your PR! By analyzing the history of the files in this pull request, we identified @pesterhazy, @jgillich and @bdimcheff to be potential reviewers.

Ah, I guess, this is broken:

$ nix-shell -p jekyll --command "jekyll new test"  
Running bundle install in /private/tmp/test... 
  Bundler: There was an error while trying to write to
  Bundler: `/nix/store/l67429rhvrmr7c4c1msb7s8zjq4fx7ad-gemfile-and-lockfile/.bundle/config`.
  Bundler: It is likely that you need to grant write permissions for that path.

Basic functionality works in my tests now. There is still a problem with building sites that depend on additional plugins (e.g. #20617), but it is there already and this PR has nothing to do with it.

LGTM – I don't immediately see a better way to handle the bundler issue. The fact that jekyll new now generates its own Gemfile makes things a little complicated for NixOS – but at least with this solution the basic tutorials for building a new site with default plugins will work. Maybe one day, commonly-used plugins could be optional arguments to the nix expression…?

@veprbl Now that I see how one patches up the installed Ruby code, this small addition to gem-config would also address #22858… but either way, I'll see how far I get upstream.

  # disable bundle install as it can't install anything in addition to what is
  # specified in pkgs/applications/misc/jekyll/Gemfile anyway. Also do chmod_R
  # to compensate for read-only files in site_template in nix store.
  jekyll = attrs: {
    postInstall = ''
      installPath=$(cat $out/nix-support/gem-meta/install-path)
      sed -i $installPath/lib/jekyll/commands/new.rb \
          -e 's@Exec.run("bundle", "install"@Exec.run("true"@' \
          -e 's@FileUtils.cp_r site_template + "/.", path@FileUtils.cp_r site_template + "/.", path; FileUtils.chmod_R "u+w", path@'
    '';
  };

@league cp_r has :preserve argument. Can't find docs for it though.

Seems to not be able to do what we want. The problem seems to be a standard one: how to get files at 0644 and directories at 0755. I don't know if this can be done beautifully enough to upstream. Might have to stick with patching in nix.

@veprbl Right. I also read (not under cp_r doc, but for copy_entry) that "If preserve is true, this method preserves owner, group, and modified time. Permissions are copied regardless preserve." https://ruby-doc.org/stdlib-2.2.2/libdoc/fileutils/rdoc/FileUtils.html

This calls for a ruby wizard :)

this is good to be merged btw