People keep confusing program configuration files and program stdin and are surprised that TOML is not a good fit for it.
If you are provisioning servers from a TOML files, you're doing it wrong. That's your program main input, not config.
If you have deeply nested values, chances are you are again confusing configuration vs main input.
JSON and CSV are great main input formats.
TOML is a great configuration format.
YAML and XML try to do both, and end up doing average on either, but being abused for all of them (looking at you Ansible and Solr).
So you should use each format for the correct purpose, as usual.
A config file looks like ~/.ssh/config or /etc/nginx/nginx.conf, not like ~/.ssh/authorized_keys or /etc/nginx/site-available/default.conf.
Just because we love to put a lot of data input in config folders (.config and /etc are full of input data) and call that configuration doesn't make it so.
How to know if something is configuration and something is input?
Conf data is usually only manually edited (authorized_keys changes with the life cycle of the program) and doesn't contain logic (default.conf if full of logic). Conf is also how the program is going to behave when performing its main task, the boostraping state, not the data used for it's main task (so not ip for provisioning servers, which is not meta, but the main course, or default.conf, which nginx uses to perform the main task). Conf rarely changes, main input often does. Conf is not piped or redirected to stdin.
If you are provisioning servers from a TOML files, you're doing it wrong. That's your program main input, not config.
If you have deeply nested values, chances are you are again confusing configuration vs main input.
JSON and CSV are great main input formats.
TOML is a great configuration format.
YAML and XML try to do both, and end up doing average on either, but being abused for all of them (looking at you Ansible and Solr).
So you should use each format for the correct purpose, as usual.
A config file looks like ~/.ssh/config or /etc/nginx/nginx.conf, not like ~/.ssh/authorized_keys or /etc/nginx/site-available/default.conf.
Just because we love to put a lot of data input in config folders (.config and /etc are full of input data) and call that configuration doesn't make it so.
How to know if something is configuration and something is input?
Conf data is usually only manually edited (authorized_keys changes with the life cycle of the program) and doesn't contain logic (default.conf if full of logic). Conf is also how the program is going to behave when performing its main task, the boostraping state, not the data used for it's main task (so not ip for provisioning servers, which is not meta, but the main course, or default.conf, which nginx uses to perform the main task). Conf rarely changes, main input often does. Conf is not piped or redirected to stdin.