nix-super/doc/manual/src/release-notes/rl-next.md

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# Release X.Y (202?-??-??)
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* `<nix/fetchurl.nix>` now accepts an additional argument `impure` which
defaults to `false`. If it is set to `true`, the `hash` and `sha256`
arguments will be ignored and the resulting derivation will have
`__impure` set to `true`, making it an impure derivation.
* If `builtins.readFile` is called on a file with context, then only the parts
of that context that appear in the content of the file are retained.
This avoids a lot of spurious errors where some benign strings end-up having
a context just because they are read from a store path
([#7260](https://github.com/NixOS/nix/pull/7260)).
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* Nix can now automatically pick UIDs for builds, removing the need to
create `nixbld*` user accounts.
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See [`auto-allocate-uids`].
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[`auto-allocate-uids`]: (../command-ref/conf-file.md#conf-auto-allocate-uids)
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* On Linux, Nix can now run builds in a user namespace where the build
runs as root (UID 0) and has 65,536 UIDs available.
<!-- FIXME: move this to its own section about system features -->
This is primarily useful for running containers such as `systemd-nspawn`
inside a Nix build. For an example, see [`tests/systemd-nspawn/nix`][nspawn].
[nspawn]: https://github.com/NixOS/nix/blob/67bcb99700a0da1395fa063d7c6586740b304598/tests/systemd-nspawn.nix.
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A build can enable this by by setting the derivation attribute:
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```
requiredSystemFeatures = [ "uid-range" ];
```
The `uid-range` [system feature] requires the [`auto-allocate-uids`]
setting to be enabled.
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[system feature]: (../command-ref/conf-file.md#conf-system-features),
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* On Linux, Nix has experimental support for running builds inside a
cgroup.
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See [`use-cgroups`](../command-ref/conf-file.md#conf-use-cgroups).
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* `nix build --json` now prints some statistics about top-level
derivations, such as CPU statistics when cgroups are enabled.