Determinate Nix 3.3: JSON logging, a new experience around hash mismatches, and more

lucperkins · April 16, 2025, 10:07pm

Here are some relevant PRs for this set of changes:

github.com/NixOS/nix

Add `json-log-path` setting

NixOS:master ← DeterminateSystems:json-log-path

opened 02:52PM - 11 Apr 25 UTC

edolstra

+228 -10

## Motivation The `json-log-path` setting specifies a path (which can be a regular file or Unix domain socket) that receives a copy of all Nix log messages (in the same format used by `--log-format internal-json` but without the `@nix ` prefixes). Internally this is implemented using the new `TeeLogger` class that dispatches log messages to multiple underlying loggers (i.e. the JSON logger and the regular progress bar). The main use case is to provide an easy way in CI to process all Nix log messages centrally to extract hash mismatches, build/substitution results, etc. ## Context --- Add :+1: to [pull requests you find important](https://github.com/NixOS/nix/pulls?q=is%3Aopen+sort%3Areactions-%2B1-desc). The Nix maintainer team uses a [GitHub project board](https://github.com/orgs/NixOS/projects/19) to [schedule and track reviews](https://github.com/NixOS/nix/tree/master/maintainers#project-board-protocol).

Move alias support from NixArgs to MultiCommand by edolstra · Pull Request #12997 · NixOS/nix · GitHub (important for upstreaming the nix profile add change)
Git fetcher: Improve error message for untracked files by edolstra · Pull Request #12870 · NixOS/nix · GitHub
JSONLogger: Acquire a lock to prevent log messages from clobbering each other by edolstra · Pull Request #12647 · NixOS/nix · GitHub
JSONLogger: Log to a file descriptor instead of another Logger by edolstra · Pull Request #12483 · NixOS/nix · GitHub

More to come soon.