Nix 2.5.0 released

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1

Hi,

I’m pleased to announce the availability of Nix 2.5.0. It is available from Download Nix / NixOS | Nix & NixOS.

Here are the release notes:

  • The garbage collector no longer blocks new builds, so the message waiting for the big garbage collector lock... is a thing of the past.

  • Binary cache stores now have a setting compression-level.

  • nix develop now has a flag --unpack to run unpackPhase.

  • Lists can now be compared lexicographically using the < operator.

  • New built-in function: builtins.groupBy, with the same functionality as Nixpkgs’ lib.groupBy, but faster.

  • nix repl now has a :log command.

The next release is scheduled for 2022-01-24.

Thank you to all the contributors!

50 Likes
2

Hi,

First, thank you for Nix 2.5!

Just, as I see a new built-in, I’m curious: is there any RFC that
described this addition to the language? Given that the RFC repo readme
explicitly mentions “Any semantic or syntactic change to the language
that is not a bug fix” and “Introduction of new interfaces or functions”
as requiring an RFC, I think a new built-in would fit the bill.

My thinking is that just dumping functions from lib into builtins to
make them faster may be a good short-term solution to slowness, but may
be a long-term hindrance by forcing nix to keep backwards-compatibility
with that forever.

So I don’t want to debate this specific addition here, but do you know
of any RFC or framework RFC that would clarify which functions should be
made into built-ins and which ones should not? And if there is currently
none, would it be possible to have one before the next addition of a
built-in, in order to avoid built-in proliferation issues?

(cc @infinisil as you appear to have made the initial PR)

7 Likes
3

The RFC process is for “when one intends to make “substantial” changes to the Nix ecosystem”, which in my opinion doesn’t apply to adding utility functions like groupBy (and I don’t think we’ve ever had an RFC about adding a builtin function). Having said that, it would be good to have some written rule about when it is appropriate to add builtin functions.

12 Likes
5

@edolstra I’ve noticed that the most recent builtin fetchers are usually exposing functionality that was added for flakes, am I correct?

6

Yes (if you mean builtins.fetchTree), but I think it requires the flakes experimental feature to be enabled.

7

I’m also talking about fetchGit and friends

8

Nixpkgs still has Nix 2.4. Why can’t I find a PR on nixpkgs for Nix 2.5?

3 Likes
9

There is one now: nix: 2.4 -> 2.5.1 by roberth · Pull Request #151419 · NixOS/nixpkgs · GitHub

3 Likes
10

Am I mistaken, but is /nix/store/trash a thing of the past as well? Is that what the “big lock” was?

1 Like
11

The trash directory existed to reduce the time window during which the garbage collector had to hold the global GC lock (since moving a big store path to trash is quick, while deleting it may be slow). Now that the collector is non-blocking, this is no longer necessary.

9 Likes