Is your feature request related to a problem? Please describe.

The config format is a bit fragile. Let's use semi-structured data instead. This enables us to accept more complex settings where it makes sense; for instance a JSON object ("attrset") would be great for configuring individual stores.

Describe the solution you'd like

Allow "nix.conf" to be specified in JSON instead.
nlohmann_json has support for stripping out comments.

No more escaping, no more text parsing, and support for a wider range of values. Great compatibility with the Nix language as well.

Describe alternatives you've considered

Configuration formats like YAML, TOML may be considered. These aren't quite as easy to generate or parse.
YAML is too fragile (Norway problem, etc)
TOML would bias our data model away from composable structures.
Nix is not actually easy to generate from Nix, and needing an evaluator to configure the evaluator would complicate initialization.

Additional context

• Triage and break up the global settings #5638

Priorities

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