forked from mirrors/nixpkgs
fc614c37c6
most modules can be evaluated for their documentation in a very restricted environment that doesn't include all of nixpkgs. this evaluation can then be cached and reused for subsequent builds, merging only documentation that has changed into the cached set. since nixos ships with a large number of modules of which only a few are used in any given config this can save evaluation a huge percentage of nixos options available in any given config. in tests of this caching, despite having to copy most of nixos/, saves about 80% of the time needed to build the system manual, or about two second on the machine used for testing. build time for a full system config shrank from 9.4s to 7.4s, while turning documentation off entirely shortened the build to 7.1s.
67 lines
2.6 KiB
Markdown
67 lines
2.6 KiB
Markdown
# Meta Attributes {#sec-meta-attributes}
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Like Nix packages, NixOS modules can declare meta-attributes to provide
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extra information. Module meta attributes are defined in the `meta.nix`
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special module.
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`meta` is a top level attribute like `options` and `config`. Available
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meta-attributes are `maintainers`, `doc`, and `buildDocsInSandbox`.
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Each of the meta-attributes must be defined at most once per module
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file.
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```nix
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{ config, lib, pkgs, ... }:
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{
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options = {
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...
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};
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config = {
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...
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};
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meta = {
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maintainers = with lib.maintainers; [ ericsagnes ];
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doc = ./default.xml;
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buildDocsInSandbox = true;
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};
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}
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```
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- `maintainers` contains a list of the module maintainers.
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- `doc` points to a valid DocBook file containing the module
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documentation. Its contents is automatically added to
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[](#ch-configuration). Changes to a module documentation have to
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be checked to not break building the NixOS manual:
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```ShellSession
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$ nix-build nixos/release.nix -A manual.x86_64-linux
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```
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- `buildDocsInSandbox` indicates whether the option documentation for the
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module can be built in a derivation sandbox. This option is currently only
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honored for modules shipped by nixpkgs. User modules and modules taken from
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`NIXOS_EXTRA_MODULE_PATH` are always built outside of the sandbox, as has
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been the case in previous releases.
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Building NixOS option documentation in a sandbox allows caching of the built
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documentation, which greatly decreases the amount of time needed to evaluate
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a system configuration that has NixOS documentation enabled. The sandbox also
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restricts which attributes may be referenced by documentation attributes
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(such as option descriptions) to the `options` and `lib` module arguments and
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the `pkgs.formats` attribute of the `pkgs` argument, `config` and the rest of
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`pkgs` are disallowed and will cause doc build failures when used. This
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restriction is necessary because we cannot reproduce the full nixpkgs
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instantiation with configuration and overlays from a system configuration
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inside the sandbox. The `options` argument only includes options of modules
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that are also built inside the sandbox, referencing an option of a module
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that isn't built in the sandbox is also forbidden.
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The default is `true` and should usually not be changed; set it to `false`
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only if the module requires access to `pkgs` in its documentation (e.g.
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because it loads information from a linked package to build an option type)
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or if its documentation depends on other modules that also aren't sandboxed
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(e.g. by using types defined in the other module).
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