Error option `gmail-britta' does not exist

[Daniel Kahlenberg]

Following

Gemfile --[bundle lock]-->
Gemfile.lock --[bundix]-->
gemset.nix --[nix develop (actual build)]-->
reproducible ruby environment

I used the example devShell and the following:

nix develop .#ruby --accept-flake-config --impure --show-trace
touch Gemfile
echo "source 'https://rubygems.org'" > Gemfile
bundle add gmail-britta --skip-install
bundle lock
bundix
# leave the devShell and rerun with generated gemset.nix this time
nix develop .#ruby --accept-flake-config --impure --show-trace

This is what I get:

error: The option `gmail-britta' does not exist. Definition values:
       - In `/nix/store/1pa0xvp1r7znaym31mkcygnqmxbksskw-source/home/misc/gemset.nix':
           {
             dependencies = [
               "haml"
             ];
             groups = [
           ...

[Daniel Kahlenberg]

See nix-community/bundix#110, not a ruby-nix issue.
Workaround is to keep gemset.nix file directly next to flake.nix or where the bundlerEnv closure is declared, as in gemset = ./gemset.nix.