Problem: Since https://github.com/NixOS/nix/pull/5226 nix profiles for
users are stored in 'XDG_STATE_HOME' or 'HOME' directory. However,
'deploy-rs' still expects profiles to be present in
'/nix/var/nix/profiles/per-user'. As a result, an attempt to deploy a
profile with newer nix may fail with an error about non-existing files.
Solution: Instead of deducing the profile path prior to ssh'ing and
actual activation, deduce the path to the profile during as a part of
'activate-rs' invocation.
Now if the profile path is not specified explicitly as an attribute in
profile within the deploy flake, the path to the profile is determined
based on the user to which the profile belongs and on the values of
'XDG_STATE_HOME' and 'HOME' variables.
Additionally, if the old profile directory (in
'/nix/var/nix/profiles/per-user') for a given user already exists, it is
used instead for the sake of backward compatibility.
Problem: 'temp_path' and 'lock_path' are handled as 'String'.
This can be a problem when the 'temp_path' directory is a symlink
on the target system, e.g. this is the case with the default
'/tmp' and macOS, where this directory is actually a symlink to '/private/tmp'.
Solution: Handle 'temp_path' and 'lock_path' as actual Paths.
Also, canonicalize 'temp_path' to avoid canary file path mismatches when checking
filesystem events.
As a side effect, also update the 'notify' dependency to the latest stable version.
* Debump the smol_str version to 0.1.16 to build on rust 1.45.2
Rust 1.45.2 is what ships in the 20.09 release, and smol_str 0.1.17 is
incompatible with it.
* Clarify version bounds on the smol_str dependency
