Add granular settings defaults (defaults.settings.{local, defined, all})

[shivaraj-bh]

resolves #261

defaults.settings.default-{current, defined, all} replaces defaults.settings.default

TODO:

• Add tests

[srid]

Nice. Quick review.

• A separate ./test/*/flake.nix would be good for testing defaults.
• Rebase new master (docs: How to work with local packages #276), and add documentation in docs/defaults.md
  • Let's elaborate the examples in the Markdown docs, and have the option description link to them.
• Not sure about the defaults.settings.default-foo naming; let me think about it.

[srid]

cf. #301

[shivaraj-bh]

added tests: 1858124

[srid]

My CI is down, but running nixci build locally fails:

$ nixci build https://github.com/srid/haskell-flake/pull/275
[..]
$ nix log /nix/store/n1qm2m8qmg3d7q25swl3h8cqxhsng9na-haskell-flake-test-0.1.0.0.drv | tail -6
warning: The interpretation of store paths arguments ending in `.drv` recently changed. If this command is now failing try again with '/nix/store/n1qm2m8qmg3d7q25swl3h8cqxhsng9na-haskell-flake-test-0.1.0.0.drv^*'
Configuring haskell-flake-test-0.1.0.0...
CallStack (from HasCallStack):
  withMetadata, called at libraries/Cabal/Cabal/src/Distribution/Simple/Utils.hs:368:14 in Cabal-3.10.1.0:Distribution.Simple.Utils
Error: Setup: Encountered missing or private dependencies:
hello

[shivaraj-bh]

My CI is down, but running nixci build locally fails:

I fixed and tested on Linux.

hello wasn’t a great example to use anyway, it isn’t a library package. I switched over to random package.

[srid]

LGTM, just not sure what emptyPackageSettings is for exactly. When I replace it with {}, the test still passes.