As `nix-daemon.service` does not make use of `ExecStop`, we prefer
to keep the socket up and available. This is important for machines
that run Nix-based services, such as automated build, test, and deploy
services, that expect the daemon socket to be available at all times.
See committed inline comment for further explanation.
The `substituters` option in `nix.settings` uses the order
of the substituters listed to define priority. Prior to https://github.com/NixOS/nixpkgs/pull/139075,
the corresponding option `binaryCaches` is declared in the `nix` namespace,
which is guaranteed to be merged last. However, the order of merging isn't
guaranteed in submodules. This cause definitions to be appended to the default
value instead of prepended, breaking backwards compatibility as reported in https://github.com/NixOS/nixpkgs/issues/158356.
The way this is addressed in the module system is with order priorities via
`mkOrder` and sorting definitions before merging. This PR restores the previous
behavior by setting a higher priority to the substituters option defined internally,
thus all definitions with default priority will be merged before it. This was chosen because
the `mkRenamedOption` function does not preserve order priority so users using legacy options do not have
precise control on placement.
This change should suffice for simple configuration, but further revision to the module system
is needed for to make various `mk*` functions aware of order priorities.
In #139075, mandatoryFeatures was removed from the generated
supportedFeatures, which breaks backward compatibility and is
different from what the description of supportedFeatures says.
Fail scripts on pipeline errors and propagate subshell errors.
If an error occurs in a subshell, including while trying to read a
secret file, we want that error to propagate to the main shell
context. That means we have to set the `inherit_errexit` option, which
allows errors from subshells to propagate to the outer shell. Also,
the subshell cannot run as part of another command, such as `export`,
since that will simply ignore the subshell exit status and only
respect `export`s exit status; first assigning the value to a variable
and then exporting it solves issue.
