have `nix flake update` better explain changes

[KiaraGrouwstra]

Is your feature request related to a problem? Please describe. Using flakes in version control allows one to fully trace what changed among your dependencies. And in fact, commands like nix flake update --commit-lock-file definitely facilitate this, committing messages along the lines of:

flake.lock: 

Flake lock file updates:

• Updated input 'nixpkgs':
    'github:nixos/nixpkgs/442d407992384ed9c0e6d352de75b69079904e4e' (2024-02-09)
  → 'github:nixos/nixpkgs/89653a03e0915e4a872788d10680e7eec92f8600' (2024-02-14)

This level of traceability is awesome, allowing users to:

• verify the exact diffs between those commits for each of those input flakes
• look up which packages received updates
• visit their change logs to read about the features and fixes in these new versions
• verify the diffs on those repo packages between those versions

While there are limits to what we can automate of those processes, I feel we might be able to improve a bit on the level of info we offer there now.

Describe the solution you'd like In commit messages for example, it could already be valuable to allow having it add info on package version updates, e.g.:

• Updated input 'nixpkgs':
    'github:nixos/nixpkgs/442d407992384ed9c0e6d352de75b69079904e4e' (2024-02-09)
  → 'github:nixos/nixpkgs/89653a03e0915e4a872788d10680e7eec92f8600' (2024-02-14)
    • vim: 1.2.3 → 1.2.4

However, for interfaces more aimed at humans, I feel we could also go further than that, like adding hyperlinks to find out more about:

• diffs for input flakes, based on the commit hashes before vs after the update
• web pages of the packages, so people can go look for change logsmeta.changelog to find out more about those version changes
• diffs for updated packages, based on the versions/revs before vs after the update

Describe alternatives you've considered stare at a list of hashes, then run

Additional context i am a fallible human being failing to always verify which packages got updated between two commit hashes

[thibaultmol]

I started with Nix recently and also stumbled into this. It's very nice that I can update from one locked state to another locked state. But it would be great if you could see exactly what packages updates between each lock. Like a chanelog basically

[thufschmitt]

This looks rather hard to do. A Nixpkgs update is likely to involve updating thousands of packages, and there's no real way to know which ones are relevant in the general case.

There could be something (but probably not built into Nix) that could add some nix diff-closures on top:

#!/usr/bin/env bash

set -euo pipefail

before_update=$(nix build --no-link --print-out-paths .)
nix flake update
after_update=$(nix build --no-link --print-out-paths .)

nix store diff-closures "$before_update" "$after_update"

 $ bash diff-closure.sh
• Updated input 'nixpkgs':
    'path:/nix/store/yy19v2dwb8ldphvia9smajvwv3ycx2c1-source?lastModified=1705331948&narHash=sha256-qjQXfvrAT1/RKDFAMdl8Hw3m4tLVvMCc8fMqzJv0pP4%3D&rev=b8dd8be3c790215716e7c12b247f45ca525867e2' (2024-01-15)
  → 'github:nixos/nixpkgs/70bdadeb94ffc8806c0570eb5c2695ad29f0e421' (2024-01-03)
bash: -41.3 KiB
gawk: 5.2.1 → 5.2.2, +15.0 KiB
glibc: 2.37-45 → 2.38-27
vim: 9.0.1441 → 9.0.2048, +860.4 KiB
xgcc: 12.2.0 → 12.3.0

[KiaraGrouwstra]

i'd mostly mentioned packages from flake-based sources, tho i guess nix flake update also updates non-flake sources. for those i wonder if we could read git tags associated with commits included in an update to get a sense of versions updated to. perhaps that would be more of a follow-up to the present ticket tho.

[gmile]

For reference, a similar topic was also discussed in discourse relatively recently: https://discourse.nixos.org/t/what-packages-will-get-updated/36057.

The commands referenced there did give me some sense of what got upgraded:

nix store diff-closures /run/*-system/

Output:

docker: 26.1.3 → 26.1.4
docker-containerd: 26.1.3 → 26.1.4
docker-init: 26.1.3 → 26.1.4
docker-runc: 26.1.3 → 26.1.4
initrd-linux: 6.6.32 → 6.6.33
linux: 6.6.32, 6.6.32-modules → 6.6.33, 6.6.33-modules, -667.3 KiB
moby: 26.1.3 → 26.1.4
nixos-system-nixos: 24.05.20240609.2819fff → 24.05.20240615.752c634
source: +68.3 KiB

However, my flake contains more stuff, packages installed using home-manager - I am not sure how to check if those packages (for example, neovim, jq, etc.) are listed here 🤔