progress-bar: use dynamic size units

[MarcelCoding]

Motivation

I've also implemented the changes from #14364 for the progress bar now.

Although it works, I am not quite happy with it.

If I copy something big from one host to another, the total size will probably be >1GiB. The problem now is that the current progress stays as 0 for way too long because the already transferred bytes are still below 0.1GiB.

and after like 10 seconds it looks like that:

This problem could be fixed by not displaying the unit only once for a X/X/X GiB block, but instead for every block: X GiB/ X GiB/X GiB.

In the reality, this could look like this: 100KiB/25MiB/1GiB. But I am afraid this could be too verbose.

Maybe the community or maintainers could express some kind of opinion in the direction this should be going.

Also, this could just be a me-problem, because I am expecting that the number is always changing because it was like that till now.

Context

---

Add 👍 to pull requests you find important.

The Nix maintainer team uses a GitHub project board to schedule and track reviews.

[xokdvium]

In the reality, this could look like this: 100KiB/25MiB/1GiB

I like this in general. If the units are the same we could skip intermediate units though and keep the last one. That would make things less verbose and reduce duplication.

[MarcelCoding]

@xokdvium I've just implemented your suggestion:

I kind of dislike that it is still kind too quiet. How about adding some kind of spinner like with npm or pnpm that indicates that nix is not frozen and still working?

[xokdvium]

kind of spinner like with npm or pnpm

Sounds great! That could be a separate PR if you'd like.

[xokdvium]

Could we maybe add an enum for the unit? Something like enum class SizeUnit

[MarcelCoding]

like its implemented now?

[xokdvium]

Suggested change

	#define SIZE_UNITS \
	X(Base, 'K') \
	#define NIX_UTIL_SIZE_UNITS \
	X(Base, 'K') \

[xokdvium]

This is more generous to the out-of-tree users of nix headers. It would also be a good idea to undefine it at the end.

[MarcelCoding]

The problem is that it is not directly clear to me where the undefine should be. Because this define is also used in the util.cc file and not only in the util.hh one.