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doc/contributing/reviewing-contributions.chapter.md

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       ## New modules {#reviewing-contributions-new-modules}

     

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       This section has been moved to [nixos/README.md](https://github.com/NixOS/nixpkgs/blob/master/nixos/README.md).

     

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       This section has been moved to [nixos/README.md](https://github.com/NixOS/nixpkgs/blob/master/nixos/README.md#new-modules).

     

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       ## Individual maintainer list {#reviewing-contributions-individual-maintainer-list}

     

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nixos/README-modular-services.md

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       # Writing and Reviewing Modular Services

     

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       ## Status

     

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       Modular Services are, as of writing, a new feature with support in NixOS.

     

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       It is in development, and be considerate of the fact that the intermediate outcome of RFC 163 is that we should try a module-based approach to portable services; it is not yet a widely agreed upon solution.

     

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       ## Relation to NixOS Modules

     

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       - A modular service is not a replacement for a NixOS module, but may be in the future.

     

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       - Using a modular service to implement a NixOS module is an expected use case, but exposes the NixOS module to a degree of uncertainty that is not acceptable for widely used modules yet.

     

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       ## Maintainership

     

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       If you contribute a modular service, you must mark yourself as maintainer of the modular service.

     

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       The maintainership of a modular service does not need to be the same as the maintainership of a NixOS module.

     

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       If you are not a maintainer of the NixOS module, you should offer to join the NixOS module's `meta.maintainers` team, so that you are included in reviews and discussions, most of which also affect the modular service.

     

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       The NixOS module maintainers have no obligation towards the modular service, except perhaps to notify you if they notice that the modular service breaks.

     

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       ## Minimum Standard

     

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       Modular services **MUST** be accompanied by a **NixOS VM test** that exercises the modular service.

     

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       Modular services **MUST** have a `meta.maintainers` module attribute that lists the maintainers of the modular service.

     

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       ## Reviewing Modular Services

     

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       When reviewing a modular service, you should check the following. Details and rationale are provided below.

     

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       ```markdown

     

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       - [ ] Has a NixOS VM test

     

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       - [ ] Has a `meta.maintainers` attribute

     

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       - [ ] Systemd-specific definitions are behind `optionalAttrs (options ? systemd)` to promote portability.

     

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       - [ ] `_class = "service"`

     

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       - [ ] Modular services provided through `passthru.services` must override the default of the package option using `finalAttrs.finalPackage`

     

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       - [ ] Is the modular services infrastructure sufficient for this service? If one or more features are not covered, comment in https://github.com/NixOS/nixpkgs/issues/428084

     

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       ```

     

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       ## Details

     

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       ### NixOS VM test

     

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       See the initial [Modular Services PR](https://github.com/NixOS/nixpkgs/pull/372170) for an [example](https://github.com/NixOS/nixpkgs/pull/372170/files#diff-e7fe16489cf3cd08ecc22b2c7896039d407a329b75691c046c95447423b3153f) of a NixOS VM test.

     

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       TBD: describe best practices here.

     

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       ### `_class = "service"`

     

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       A [`_class`](https://nixos.org/manual/nixpkgs/unstable/#module-system-lib-evalModules-param-class) declaration ensures a clear error when the module is accidentally imported into a configuration that isn't a modular service, such as a NixOS configuration.

     

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       Provide it as the first attribute in the module:

     

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       ```nix

     

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       { lib, config, ... }:

     

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       {

     

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         _class = "service";

     

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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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       }

     

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       ```

     

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       ### Overriding the package default

     

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       When a modular service is provided through `passthru.services`, it must override the default of the package option using [`finalAttrs.finalPackage`](https://nixos.org/manual/nixpkgs/unstable/#mkderivation-recursive-attributes).

     

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       If this is not possible, or if the module is not represented by a single package, consider exposing the modular service directly by file path only.

     

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       Otherwise, since some packages are *defined* by an override, the modular service would launch a wrong package, if it builds at all.

     

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       Example:

     

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       `package.nix`

     

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       ```nix

     

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       {

     

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         stdenv,

     

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         nixosTests,

     

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       # ...

     

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       }:

     

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       stdenv.mkDerivation (finalAttrs: {

     

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         pname = "example";

     

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         # ...

     

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         passthru = {

     

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           services = {

     

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             default = {

     

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               imports = [ ./service.nix ];

     

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               example.package = finalAttrs.finalPackage;

     

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               # ...

     

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             };

     

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           };

     

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         };

     

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       })

     

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       ```

nixos/README.md

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       ##### Comments

     

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       ```

     

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       See also [./README-modular-services.md](./README-modular-services.md).

nixos/doc/manual/development/modular-services.md

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       <!-- TODO example of a single-instance service -->

     

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       ## Writing and Reviewing a Modular Service {#modular-service-review}

     

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       Refer to the contributor documentation in [`nixos/README-modular-services.md`](https://github.com/NixOS/nixpkgs/blob/master/nixos/README-modular-services.md).

     

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       ## Portable Service Options {#modular-service-options-portable}

     

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       ```{=include=} options

nixos/doc/manual/redirects.json

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         "modular-service-portability": [

     

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           "index.html#modular-service-portability"

     

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         ],

     

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         "modular-service-review": [

     

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           "index.html#modular-service-review"

     

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         ],

     

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         "modular-services": [

     

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           "index.html#modular-services"

     

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         ],