uv: add manual entry (#430257)

vcpkg.section.md

weechat.section.md

xorg.section.md

uv.section.md

build-support.md

```

# uv {#sec-uv}

`uv` is an extremely fast Python package installer and resolver, written in Rust.

It manages project dependencies and environments, with support for lockfiles, workspaces, and more.

Due to `uv` being unaware that it is running on a NixOS system, by default, it will fetch dynamically-linked Python executables that will fail to run, as NixOS cannot run executables intended for generic Linux environments out of the box.

To learn more on this, please visit

https://nix.dev/guides/faq.html#how-to-run-non-nix-executables

There are two ways to mitigate this:

1. Provide `uv` with a statically-linked Python executable (ideally from `nixpkgs`) via the [`UV_PYTHON` environment variable](https://docs.astral.sh/uv/reference/environment/#uv_python). Alternatively, the `--python` flag can also be used, but this is easy to forget. It is also helpful to forbid `uv` from downloading any Python binaries via the [`UV_PYTHON_DOWNLOADS` environment variable](https://docs.astral.sh/uv/reference/environment/#uv_python_downloads) by setting it to `never`.

These variables can be set in `shell.nix` and `.env` files, which can be redistributed with the project to ensure other NixOS machines can execute the project.

2. Add `programs.nix-ld.enable = true` to your NixOS config. While functional, the previous option is to be preferred, as this is the "works on my machine" option, because redistributing Python projects that use `uv` to another NixOS machine that does not have `nix-ld` enabled will cause the same errors to occur.

Additionally, there is the issue of modules from PyPI vendoring dynamically-linked libraries, such as `numpy`, which will also fail to work.

This topic is not local to `uv`, but is deserving of documentation nonetheless.

Setting `LD_LIBRARY_PATH` should be the solution of choice here. Either:

1. Use `lib.makeLibraryPath` to set `LD_LIBRARY_PATH` from a `shell.nix`, e.g. `LD_LIBRARY_PATH = lib.makeLibraryPath [ pkgs.openssl pkgs.zlib pkgs.curl ]`

2. (If you have already enabled `nix-ld`) set `LD_LIBRARY_PATH` to `NIX_LD_LIBRARY_PATH`. Be aware this is not a silver bullet solution, as this simply provides a list of commonly used libraries, as is shown in `nixos/modules/programs/nix-ld.nix`.

  "sec-interop.cylonedx-fod": [

    "index.html#sec-interop.cylonedx-fod"

  ],

  "sec-uv": [

    "index.html#sec-uv"

  ],

  "module-system-module-argument-_prefix": [

    "index.html#module-system-module-argument-_prefix"

  ],

  meta = {

    description = "Extremely fast Python package installer and resolver, written in Rust";

    longDescription = ''

      `uv` manages project dependencies and environments, with support for lockfiles, workspaces, and more.

      Due to `uv`'s (over)eager fetching of dynamically-linked Python executables,

      as well as vendoring of dynamically-linked libraries within Python modules distributed via PyPI,

      NixOS users can run into issues when managing Python projects.

      See the Nixpkgs Reference Manual entry for `uv` for information on how to mitigate these issues:

      https://nixos.org/manual/nixpkgs/unstable/#sec-uv.

      For building Python projects with `uv` and Nix outside of nixpkgs, check out `uv2nix` at https://github.com/pyproject-nix/uv2nix.

    '';

    homepage = "https://github.com/astral-sh/uv";

    changelog = "https://github.com/astral-sh/uv/blob/${finalAttrs.version}/CHANGELOG.md";

    license = with lib.licenses; [