[nix] Simplify profile priority, make it match flake file

[mikeland73]

Summary

I was implementing a progress indicator for global install, and the profile install retry logic was making it a bit complicated. I then realized that the order we were assigning to priorities (latter package takes precedence) is actually inverse to what flake buildInputs does (it uses earlier precedence). In practice, this means the profile generated by devbox and the flake generated by devbox would have different behaviors. This is not terrible but also not ideal. So I removed the sorting and added some documentation to ensure we always keep the same (local, global) order.

Finally, I tried out a slightly different approach which doesn't require a profile install with retries. By reading the profile manifest file we're able to see what the highest number existing priority (lowest priority) is and just increment it to achieve the next lowest priority. I tried this up to numbers in the thousands there doesn't seem to be any limits.

Some benefits of this approach:

• It's easier to implement progress indicators that read stdout/err in a goroutine.
• Better performance (no retries needed)
• more deterministic
• Code is a bit simpler

Drawbacks:

• Depends on the manifest
• Needlessly assigns more priorities than are needed

@savil curious your thoughts on this?

How was it tested?

devbox global add php82
devbox add php
devbox run "php -v"

[savil]

Oh good catch on the buildInputs behavior. Just to confirm: did you try it out to verify?
Asking because I'd heard the inverse last time and so implemented that order :)

I really like the clever implementation using the priority from manifest.json!

[savil]

in line 227 above, lets add:

fmt.Fprintf(args.Writer, "%s: ", stepMsg)
color.New(color.FgRed).Fprintf(args.Writer, "Fail\n")

[mikeland73]

Do you mind if I push this to the stacked diff? That changes this logic because it no longer uses custom stdout

That way I can test how this will look with the new tty nix command.

[savil]

I'm glad flakes changed the manifest from .nix to .json so we can do this :)

[mikeland73]

@savil yeah, I think I was wrong on precedence before: