TOML sucks for list of tables simply because they intentionally crippled inline tables to only be able to occupy one line. For ideology reasons ("we don't need to add a pseudo-JSON"). Unless your table is small, it's going to look absolutely terrible being all crammed into one line.

https://github.com/toml-lang/toml/issues/516

The official way to do list of tables is (look at how much duplication there is)

  [[main_app.general_settings.logging.handlers]]
    name = "default"
    output = "stdout"
    level = "info"

  [[main_app.general_settings.logging.handlers]]
    name = "stderr"
    output = "stderr"
    level = "error"

  [[main_app.general_settings.logging.handlers]]
    name = "access"
    output = "/var/log/access.log"
    level = "info"

vs

  handlers = [
    {
      name = "default",
      output =  "stdout",
      level = "info",
    }, {
      name = "stderr",
      output =  "stderr",
      level = "error",
    }, {
      name = "access",
      output =  "/var/log/access.log",
      level = "info",
    },
  ]

I would still reach for TOML first if I only needed simple key-value configuration (never YAML), but for anything requiring list-of-tables I would seriously consider JSON with trailing commas instead.

I see the point and this is certainly a drawback of TOML but for me this is something of a boundary case between configuration and data.

When configuration gets so complicated that the configuration starts to resemble structured data I tend to prefer to switch to a real scripting language and generate JSON instead.

Expression languages like Nix, Jsonnet, Dhall, and Cue are really nice in these situations.

for this reason I couldn't see a CI platform ever seriously consider TOML

(someone may point out to me a CI platform that relies on TOML—which I welcome)

Rust is built on TOML. For better or worse.

Do you mean Cargo? Because Cargo is not a CI system. You never embed shell commands in a Cargo.toml.

If you need to program complex logic to build a crate, you don’t write TOML. You write a build.rs file in actual Rust.

If embedding shell commands in a configuration language is considered a CI system I think we are doomed.

> JSON with trailing commas

JSON5?

It's perfect until you do a lot of nesting..

...or any nesting. TOML sucks for anything non-trivial.

It makes me sad every time I see a newly announced tool that went for YAML instead of TOML.