Add a use-registries config option (and deprecate --no-registries )

[balsoft]

Some people want to avoid using registries at all on their system; Instead
of having to add --no-registries to every command, this commit allows to
set registries = false in the config. --no-registries is still allowed
everywhere it was allowed previously, but now as a shorthand to --option
registries false rather than a separate flag.

[thufschmitt]

Some people want to avoid using registries at all on their system

Isn’t it simpler to just set flake-registry to an empty registry in that case? (possibly making the empty file or empty json object a valid registry to make this even simpler)

[balsoft]

Isn’t it simpler to just set flake-registry to an empty registry in that case?

That was my first thought as well, but emptying flake-registry still leaves a system registry (/etc/nix/registry.json) and a user registry ($XDG_CONFIG_HOME/nix/registry.json). This option disables registries completely.

[nrdxp]

Until this is merged, it is also possible to simply specify an empty registry, to simulate no registry:

# registry.json
{
  "version": 2
}

But I agree that a config option is better.

[balsoft]

Until this is merged, it is also possible to simply specify an empty registry, to simulate no registry:

Once again, this doesn't quite work since there are also user and system registries.

[edolstra]

A tristate is confusing to me, maybe it should just be initialized to settings.registries?

[balsoft]

I have thought about this a bit, I don't like initializing fields with global state. It may be confusing if the state changes after the structure has been initialized, since then lockFlags.useRegistries may go out of sync with settings.useRegistries.