Release 2.32.0 (2025-10-06)
Incompatible changes
-
Removed support for daemons and clients older than Nix 2.0 #13951
We have dropped support in the daemon worker protocol for daemons and clients that don't speak at least version 18 of the protocol. This first Nix release that supports this version is Nix 2.0, released in February 2018.
-
Derivation JSON format now uses store path basenames only #13570 #13980
Experience with many JSON frameworks (e.g. nlohmann/json in C++, Serde in Rust, and Aeson in Haskell) has shown that the use of the store directory in JSON formats is an impediment to systematic JSON formats, because it requires the serializer/deserializer to take an extra paramater (the store directory).
We ultimately want to rectify this issue with all JSON formats to the extent allowed by our stability promises. To start with, we are changing the JSON format for derivations because the
nix derivation
commands are — in addition to being formally unstable — less widely used than other unstable commands.See the documentation on the JSON format for derivations for further details.
-
C API:
nix_get_attr_name_byidx
,nix_get_attr_byidx
take anix_value *
instead ofconst nix_value *
#13987In order to accommodate a more optimized internal representation of attribute set merges these functions require a mutable
nix_value *
that might be modified on access. This does not break the ABI of these functions.
New features
-
C API: Add lazy attribute and list item accessors #14030
The C API now includes lazy accessor functions for retrieving values from lists and attribute sets without forcing evaluation:
nix_get_list_byidx_lazy()
- Get a list element without forcing its evaluationnix_get_attr_byname_lazy()
- Get an attribute value by name without forcing evaluationnix_get_attr_byidx_lazy()
- Get an attribute by index without forcing evaluation
These functions are useful when forwarding unevaluated sub-values to other lists, attribute sets, or function calls. They allow more efficient handling of Nix values by deferring evaluation until actually needed.
Additionally, bounds checking has been improved for all
_byidx
functions to properly validate indices before access, preventing potential out-of-bounds errors.The documentation for
NIX_ERR_KEY
error handling has also been clarified to specify when this error code is returned. -
HTTP binary caches now support transparent compression for metadata
HTTP binary cache stores can now compress
.narinfo
,.ls
, and build log files before uploading them, reducing bandwidth usage and storage requirements. The compression is applied transparently using theContent-Encoding
header, allowing compatible clients to automatically decompress the files.Three new configuration options control this behavior:
narinfo-compression
: Compression method for.narinfo
filesls-compression
: Compression method for.ls
fileslog-compression
: Compression method for build logs inlog/
directory
Example usage:
nix copy --to 'http://cache.example.com?narinfo-compression=gzip&ls-compression=gzip' /nix/store/... nix store copy-log --to 'http://cache.example.com?log-compression=br' /nix/store/...
-
Temporary build directories no longer include derivation names #13839
Temporary build directories created during derivation builds no longer include the derivation name in their path to avoid build failures when the derivation name is too long. This change ensures predictable prefix lengths for build directories under
/nix/var/nix/builds
. -
External derivation builders #14145
These are helper programs that Nix calls to perform derivations for specified system types, e.g. by using QEMU to emulate a different type of platform. For more information, see the
external-builders
setting.This is currently an experimental feature.
Performance improvements
-
Optimize memory usage of attribute set merges #13987
Attribute set update operations have been optimized to reduce reallocations in cases when the second operand is small.
For typical evaluations of nixpkgs this optimization leads to ~20% less memory allocated in total without significantly affecting evaluation performance.
-
Substituted flake inputs are no longer re-copied to the store #14041
Since 2.25, Nix would fail to store a cache entry for substituted flake inputs, which in turn would cause them to be re-copied to the store on initial evaluation. Caching these inputs results in a near doubling of performance in some cases — especially on I/O-bound machines and when using commands that fetch many inputs, like
nix flake [archive|prefetch-inputs]
. -
nix flake check
now skips derivations that can be substituted #13574Previously,
nix flake check
would evaluate and build/substitute all derivations. Now, it will skip downloading derivations that can be substituted. This can drastically decrease the time invocations take in environments where checks may already be cached (like in CI). -
fetchTarball
andfetchurl
now correctly substitute (#14138)At some point we stopped substituting calls to
fetchTarball
andfetchurl
with a setnarHash
to avoid incorrectly substituting things infetchTree
, even though it would be safe to substitute when calling the legacyfetch{Tarball,url}
. This fixes that regression where it is safe. -
Started moving AST allocations into a bump allocator #14088
This leaves smaller, immutable structures in the AST. So far this saves about 2% memory on a NixOS config evaluation.
Contributors
This release was made possible by the following 32 contributors:
- Farid Zakaria (@fzakaria)
- dram (@dramforever)
- Ephraim Siegfried (@EphraimSiegfried)
- Robert Hensing (@roberth)
- Taeer Bar-Yam (@Radvendii)
- Emily (@emilazy)
- Jens Petersen (@juhp)
- Bernardo Meurer (@lovesegfault)
- Jörg Thalheim (@Mic92)
- Leandro Emmanuel Reina Kiperman (@kip93)
- Marie (@NyCodeGHG)
- Ethan Evans (@ethanavatar)
- Yaroslav Bolyukin (@CertainLach)
- Matej Urbas (@urbas)
- Jami Kettunen (@JamiKettunen)
- Clayton (@netadr)
- Grégory Marti (@gmarti)
- Eelco Dolstra (@edolstra)
- rszyma (@rszyma)
- Philip Wilk (@philipwilk)
- John Ericson (@Ericson2314)
- Tom Westerhout (@twesterhout)
- Tristan Ross (@RossComputerGuy)
- Sergei Zimmerman (@xokdvium)
- Jean-François Roche (@jfroche)
- Seth Flynn (@getchoo)
- éclairevoyant (@eclairevoyant)
- Glen Huang (@hgl)
- osman - オスマン (@osbm)
- David McFarland (@corngood)
- Cole Helbling (@cole-h)
- Sinan Mohd (@sinanmohd)
- Philipp Otterbein