pkgs/by-name: Introduce

This introduces the `pkgs/by-name` directory as proposed by RFC 140.
Included are:
- The implementation to add packages defined in that directory to the
  top-level package scope
- Contributer documentation on how to add packages to it
- A GitHub Actions workflow to check the structure of it on all PRs
This commit is contained in:
Silvan Mosberger 2023-08-31 22:41:09 +02:00
parent bb34f4d1a6
commit f6467c3574
6 changed files with 213 additions and 1 deletions

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# pkgs/by-name
/pkgs/test/nixpkgs-check-by-name @infinisil
/pkgs/by-name/README.md @infinisil
/pkgs/top-level/by-name-overlay.nix @infinisil
/.github/workflows/check-by-name.nix @infinisil
# Nixpkgs build-support
/pkgs/build-support/writers @lassulus @Profpatsch

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# Checks pkgs/by-name (see pkgs/by-name/README.md)
# using the nixpkgs-check-by-name tool (see pkgs/test/nixpkgs-check-by-name)
name: Check pkgs/by-name
# The pre-built tool is fetched from a channel,
# making it work predictable on all PRs
on: pull_request
# The tool doesn't need any permissions, it only outputs success or not based on the checkout
permissions: {}
jobs:
check:
# This is x86_64-linux, for which the tool is always prebuilt on the nixos-* channels,
# as specified in nixos/release-combined.nix
runs-on: ubuntu-latest
steps:
- uses: actions/checkout@v3
- uses: cachix/install-nix-action@v22
- name: Determining channel to use for dependencies
run: |
echo "Determining which channel to use for PR base branch $GITHUB_BASE_REF"
if [[ "$GITHUB_BASE_REF" =~ ^(release|staging|staging-next)-([0-9][0-9]\.[0-9][0-9])$ ]]; then
# Use the release channel for all PRs to release-XX.YY, staging-XX.YY and staging-next-XX.YY
channel=nixos-${BASH_REMATCH[2]}
echo "PR is for a release branch, using release channel $channel"
else
# Use the nixos-unstable channel for all other PRs
channel=nixos-unstable
echo "PR is for a non-release branch, using unstable channel $channel"
fi
echo "channel=$channel" >> "$GITHUB_ENV"
- name: Fetching latest version of channel
run: |
echo "Fetching latest version of channel $channel"
# This is probably the easiest way to get Nix to output the path to a downloaded channel!
nixpkgs=$(nix-instantiate --find-file nixpkgs -I nixpkgs=channel:"$channel")
# This file only exists in channels
rev=$(<"$nixpkgs"/.git-revision)
echo "Channel $channel is at revision $rev"
echo "nixpkgs=$nixpkgs" >> "$GITHUB_ENV"
echo "rev=$rev" >> "$GITHUB_ENV"
- name: Fetching pre-built nixpkgs-check-by-name from the channel
run: |
echo "Fetching pre-built nixpkgs-check-by-name from channel $channel at revision $rev"
# Passing --max-jobs 0 makes sure that we won't build anything
nix-build "$nixpkgs" -A tests.nixpkgs-check-by-name --max-jobs 0
- name: Running nixpkgs-check-by-name
run: result/bin/nixpkgs-check-by-name .

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# Name-based package directories
The structure of this directory maps almost directly to top-level package attributes.
This is the recommended way to add new top-level packages to Nixpkgs [when possible](#limitations).
## Example
The top-level package `pkgs.some-package` may be declared by setting up this file structure:
```
pkgs
└── by-name
├── so
┊ ├── some-package
┊ └── package.nix
```
Where `some-package` is the package name and `so` is the lowercased 2-letter prefix of the package name.
The `package.nix` may look like this:
```nix
# A function taking an attribute set as an argument
{
# Get access to top-level attributes for use as dependencies
lib,
stdenv,
libbar,
# Make this derivation configurable using `.override { enableBar = true }`
enableBar ? false,
}:
# The return value must be a derivation
stdenv.mkDerivation {
# ...
buildInputs =
lib.optional enableBar libbar;
}
```
You can also split up the package definition into more files in the same directory if necessary.
Once defined, the package can be built from the Nixpkgs root directory using:
```
nix-build -A some-package
```
See the [general package conventions](../README.md#conventions) for more information on package definitions.
### Changing implicit attribute defaults
The above expression is called using these arguments by default:
```nix
{
lib = pkgs.lib;
stdenv = pkgs.stdenv;
libbar = pkgs.libbar;
}
```
But the package might need `pkgs.libbar_2` instead.
While the function could be changed to take `libbar_2` directly as an argument,
this would change the `.override` interface, breaking code like `.override { libbar = ...; }`.
So instead it is preferable to use the same generic parameter name `libbar`
and override its value in [`pkgs/top-level/all-packages.nix`](../top-level/all-packages.nix):
```nix
libfoo = callPackage ../by-name/so/somePackage/package.nix {
libbar = libbar_2;
};
```
## Limitations
There's some limitations as to which packages can be defined using this structure:
- Only packages defined using `pkgs.callPackage`.
This excludes packages defined using `pkgs.python3Packages.callPackage ...`.
Instead use the [category hierarchy](../README.md#category-hierarchy) for such attributes.
- Only top-level packages.
This excludes packages for other package sets like `pkgs.pythonPackages.*`.
Refer to the definition and documentation of the respective package set to figure out how such packages can be declared.
## Validation
CI performs [certain checks](../test/nixpkgs-check-by-name/README.md#validity-checks) on the `pkgs/by-name` structure.
This is done using the [`nixpkgs-check-by-name` tool](../test/nixpkgs-check-by-name).
The version of this tool used is the one that corresponds to the NixOS channel of the PR base branch.
See [here](../../.github/workflows/check-by-name.yml) for details.
The tool can be run locally using
```bash
nix-build -A tests.nixpkgs-check-by-name
result/bin/nixpkgs-check-by-name .
```

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# Nixpkgs pkgs/by-name checker
This directory implements a program to check the [validity](#validity-checks) of the `pkgs/by-name` Nixpkgs directory once introduced.
It is being used by [this GitHub Actions workflow](../../../.github/workflows/check-by-name.yml).
This is part of the implementation of [RFC 140](https://github.com/NixOS/rfcs/pull/140).
## API
This API may be changed over time if the CI making use of it is adjusted to deal with the change appropriately, see [Hydra builds](#hydra-builds).
This API may be changed over time if the CI workflow making use of it is adjusted to deal with the change appropriately.
- Command line: `nixpkgs-check-by-name <NIXPKGS>`
- Arguments:

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# This file turns the pkgs/by-name directory (see its README.md for more info) into an overlay that adds all the defined packages.
# No validity checks are done here,
# instead this file is optimised for performance,
# and validity checks are done by CI on PRs.
# Type: Path -> Overlay
baseDirectory:
let
# Because of Nix's import-value cache, importing lib is free
lib = import ../../lib;
inherit (builtins)
readDir
;
inherit (lib.attrsets)
mapAttrs
mapAttrsToList
mergeAttrsList
;
# Package files for a single shard
# Type: String -> String -> AttrsOf Path
namesForShard = shard: type:
if type != "directory" then
# Ignore all non-directories. Technically only README.md is allowed as a file in the base directory, so we could alternatively:
# - Assume that README.md is the only file and change the condition to `shard == "README.md"` for a minor performance improvement.
# This would however cause very poor error messages if there's other files.
# - Ensure that README.md is the only file, throwing a better error message if that's not the case.
# However this would make for a poor code architecture, because one type of error would have to be duplicated in the validity checks and here.
# Additionally in either of those alternatives, we would have to duplicate the hardcoding of "README.md"
{ }
else
mapAttrs
(name: _: baseDirectory + "/${shard}/${name}/package.nix")
(readDir (baseDirectory + "/${shard}"));
# The attribute set mapping names to the package files defining them
# This is defined up here in order to allow reuse of the value (it's kind of expensive to compute)
# if the overlay has to be applied multiple times
packageFiles = mergeAttrsList (mapAttrsToList namesForShard (readDir baseDirectory));
in
# TODO: Consider optimising this using `builtins.deepSeq packageFiles`,
# which could free up the above thunks and reduce GC times.
# Currently this would be hard to measure until we have more packages
# and ideally https://github.com/NixOS/nix/pull/8895
self: super:
mapAttrs (name: file:
self.callPackage file { }
) packageFiles

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arguments. Normal users should not import this directly but instead
import `pkgs/default.nix` or `default.nix`. */
let
# An overlay to auto-call packages in ../by-name.
# By defining it at the top of the file,
# this value gets reused even if this file is imported multiple times,
# thanks to Nix's import-value cache.
autoCalledPackages = import ./by-name-overlay.nix ../by-name;
in
{ ## Misc parameters kept the same for all stages
##
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stdenvAdapters
trivialBuilders
splice
autoCalledPackages
allPackages
otherPackageSets
aliases