We had fields set to the same values before in our test data. This is
not a problem per-se, but does mean we wouldn't catch certain mixups.
Now, the fields are set to distinct values (where possible), which makes
the test more robust.
This requires that we refer to the `sourceInfo` instead of the
`result`. However, `sourceInfo` does not create a chain of basedir
resolution, so we add that back with `flakeDir`.
Only a much smaller `StructuredAttrs` remains, the rest is is now moved
to `DerivationOptions`.
This gets us quite close to `std::optional<StructuredAttrs>` and
`DerivationOptions` being included in `Derivation` as fields.
Now, both the unit and functional tests relating to derivation options
are tested both ways -- with input addressing and content-addressing
derivations.
This is a small optimization used when we're signing a narinfo for
multiple keys in one go. Using this sign variant, we only compute the
NAR fingerprint once, then sign it with all the keys.
It is just use for adding context to errors, but we have `addTrace` to
do that. Let the callers do that instead.
The callers doing so is a bit duplicated, yes, but this will get better
once `DerivationOptions` is included in `Derivation`.
The STSProfileCredentialsProviders allows to assume a specific IAM role
when accessing an S3 repository. Sometimes this is needed to obtain the
permissions to operate on the bucket.
Nix shipping with Yet Another Programming Language is often questioned
among beginners. This change highlights distinctive aspects of the Nix
language to ease the learning curve and better orient readers around
what really matters for using Nix.
Since it's on topic, this change also polishes the wording on the motivation for string contexts.
This change follows the definition from aptitude, but using precise notions from Nix:
> package managers deal with packages: collections of files that are
> bundled together and can be installed and removed as a group.
> [...]
> If a package A depends upon another package B, then B is required
> for A to operate properly.
> [...]
> The job of a package manager is to present an interface which assists
> the user in managing the collection of packages installed on his or her system.
>
> -- <https://www.debian.org/doc/manuals/aptitude/pr01s02.en.html>
An interesting addition:
> Packages are abstractions defining the granularity at which users can act
> (add, remove, upgrade, etc.) on available software.
> A distribution is a collection of packages maintained (hopefully) coherently.
>
> -- Package Upgrades in FOSS Distributions: Details and Challenges
> (Roberto Di Cosmo, Stefano Zacchiroli; 2009) <https://arxiv.org/pdf/0902.1610>
Notably these quotes and this change don't say anything about installation,
or what it means for software to be available. In practice, this is
handled downstream, e.g. in NixOS or Home Manager. Nix historically
provides rudimentary facilities for package management such as
`nix-env`, but I claim they are widely agreed upon being discouraged,
with plenty of arguments provided in <https://stop-using-nix-env.privatevoid.net>.
Similarly, the specific structure of packages is determined downstream,
since Nix is policy-free:
> Nix is policy-free; it provides mechanisms to implement various deployment policies, but does not enforce a specific one.
>
> -- The Purely Functional Software Deployment Model (Eelco Dolstra; 2006) <https://edolstra.github.io/pubs/phd-thesis.pdf>
Specifically, Nix mechanisms do not define what a package is supposed to be:
> It's worth noting that the Nix language is intended as a DSL for package and configuration management, but it has no notions of "packages" or "configurations".
>
> -- <https://gist.github.com/edolstra/29ce9d8ea399b703a7023073b0dbc00d>
This is why we say, Nix *allows* denoting packages in a certain way, but
doesn't enforce any particular way.
Rather than "mounting" the store inside an empty virtual filesystem,
just return the store as a virtual filesystem. This is more modular.
(FWIW, it also supports two long term hopes of mind:
1. More capability-based Nix language mode. I dream of a "super pure
eval" where you can only use relative path literals (See #8738), and
any `fetchTree`-fetched stuff + the store are all disjoint (none is
mounted in another) file systems.
2. Windows, where the store dir may include drive letters, etc., and is
thus unsuitable to be the prefix of any `CanonPath`s.
)
Co-authored-by: Eelco Dolstra <edolstra@gmail.com>
