pyrox.dev
1# Coding conventions {#chap-conventions}
2
3## Syntax {#sec-syntax}
4
5- Use 2 spaces of indentation per indentation level in Nix expressions, 4 spaces in shell scripts.
6
7- Do not use tab characters, i.e. configure your editor to use soft tabs. For instance, use `(setq-default indent-tabs-mode nil)` in Emacs. Everybody has different tab settings so it’s asking for trouble.
8
9- Use `lowerCamelCase` for variable names, not `UpperCamelCase`. Note, this rule does not apply to package attribute names, which instead follow the rules in [](#sec-package-naming).
10
11- Function calls with attribute set arguments are written as
12
13 ```nix
14 foo {
15 arg = ...;
16 }
17 ```
18
19 not
20
21 ```nix
22 foo
23 {
24 arg = ...;
25 }
26 ```
27
28 Also fine is
29
30 ```nix
31 foo { arg = ...; }
32 ```
33
34 if it's a short call.
35
36- In attribute sets or lists that span multiple lines, the attribute names or list elements should be aligned:
37
38 ```nix
39 # A long list.
40 list = [
41 elem1
42 elem2
43 elem3
44 ];
45
46 # A long attribute set.
47 attrs = {
48 attr1 = short_expr;
49 attr2 =
50 if true then big_expr else big_expr;
51 };
52
53 # Combined
54 listOfAttrs = [
55 {
56 attr1 = 3;
57 attr2 = "fff";
58 }
59 {
60 attr1 = 5;
61 attr2 = "ggg";
62 }
63 ];
64 ```
65
66- Short lists or attribute sets can be written on one line:
67
68 ```nix
69 # A short list.
70 list = [ elem1 elem2 elem3 ];
71
72 # A short set.
73 attrs = { x = 1280; y = 1024; };
74 ```
75
76- Breaking in the middle of a function argument can give hard-to-read code, like
77
78 ```nix
79 someFunction { x = 1280;
80 y = 1024; } otherArg
81 yetAnotherArg
82 ```
83
84 (especially if the argument is very large, spanning multiple lines).
85
86 Better:
87
88 ```nix
89 someFunction
90 { x = 1280; y = 1024; }
91 otherArg
92 yetAnotherArg
93 ```
94
95 or
96
97 ```nix
98 let res = { x = 1280; y = 1024; };
99 in someFunction res otherArg yetAnotherArg
100 ```
101
102- The bodies of functions, asserts, and withs are not indented to prevent a lot of superfluous indentation levels, i.e.
103
104 ```nix
105 { arg1, arg2 }:
106 assert system == "i686-linux";
107 stdenv.mkDerivation { ...
108 ```
109
110 not
111
112 ```nix
113 { arg1, arg2 }:
114 assert system == "i686-linux";
115 stdenv.mkDerivation { ...
116 ```
117
118- Function formal arguments are written as:
119
120 ```nix
121 { arg1, arg2, arg3 }:
122 ```
123
124 but if they don't fit on one line they're written as:
125
126 ```nix
127 { arg1, arg2, arg3
128 , arg4, ...
129 , # Some comment...
130 argN
131 }:
132 ```
133
134- Functions should list their expected arguments as precisely as possible. That is, write
135
136 ```nix
137 { stdenv, fetchurl, perl }: ...
138 ```
139
140 instead of
141
142 ```nix
143 args: with args; ...
144 ```
145
146 or
147
148 ```nix
149 { stdenv, fetchurl, perl, ... }: ...
150 ```
151
152 For functions that are truly generic in the number of arguments (such as wrappers around `mkDerivation`) that have some required arguments, you should write them using an `@`-pattern:
153
154 ```nix
155 { stdenv, doCoverageAnalysis ? false, ... } @ args:
156
157 stdenv.mkDerivation (args // {
158 ... if doCoverageAnalysis then "bla" else "" ...
159 })
160 ```
161
162 instead of
163
164 ```nix
165 args:
166
167 args.stdenv.mkDerivation (args // {
168 ... if args ? doCoverageAnalysis && args.doCoverageAnalysis then "bla" else "" ...
169 })
170 ```
171
172- Unnecessary string conversions should be avoided. Do
173
174 ```nix
175 rev = version;
176 ```
177
178 instead of
179
180 ```nix
181 rev = "${version}";
182 ```
183
184- Building lists conditionally _should_ be done with `lib.optional(s)` instead of using `if cond then [ ... ] else null` or `if cond then [ ... ] else [ ]`.
185
186 ```nix
187 buildInputs = lib.optional stdenv.isDarwin iconv;
188 ```
189
190 instead of
191
192 ```nix
193 buildInputs = if stdenv.isDarwin then [ iconv ] else null;
194 ```
195
196 As an exception, an explicit conditional expression with null can be used when fixing a important bug without triggering a mass rebuild.
197 If this is done a follow up pull request _should_ be created to change the code to `lib.optional(s)`.
198
199- Arguments should be listed in the order they are used, with the exception of `lib`, which always goes first.
200
201## Package naming {#sec-package-naming}
202
203The key words _must_, _must not_, _required_, _shall_, _shall not_, _should_, _should not_, _recommended_, _may_, and _optional_ in this section are to be interpreted as described in [RFC 2119](https://tools.ietf.org/html/rfc2119). Only _emphasized_ words are to be interpreted in this way.
204
205In Nixpkgs, there are generally three different names associated with a package:
206
207- The `name` attribute of the derivation (excluding the version part). This is what most users see, in particular when using `nix-env`.
208
209- The variable name used for the instantiated package in `all-packages.nix`, and when passing it as a dependency to other functions. Typically this is called the _package attribute name_. This is what Nix expression authors see. It can also be used when installing using `nix-env -iA`.
210
211- The filename for (the directory containing) the Nix expression.
212
213Most of the time, these are the same. For instance, the package `e2fsprogs` has a `name` attribute `"e2fsprogs-version"`, is bound to the variable name `e2fsprogs` in `all-packages.nix`, and the Nix expression is in `pkgs/os-specific/linux/e2fsprogs/default.nix`.
214
215There are a few naming guidelines:
216
217- The `pname` attribute _should_ be identical to the upstream package name.
218
219- The `pname` and the `version` attribute _must not_ contain uppercase letters — e.g., `"mplayer" instead of `"MPlayer"`.
220
221- The `version` attribute _must_ start with a digit e.g`"0.3.1rc2".
222
223- If a package is not a release but a commit from a repository, then the `version` attribute _must_ be the date of that (fetched) commit. The date _must_ be in `"unstable-YYYY-MM-DD"` format.
224
225- Dashes in the package `pname` _should_ be preserved in new variable names, rather than converted to underscores or camel cased — e.g., `http-parser` instead of `http_parser` or `httpParser`. The hyphenated style is preferred in all three package names.
226
227- If there are multiple versions of a package, this _should_ be reflected in the variable names in `all-packages.nix`, e.g. `json-c_0_9` and `json-c_0_11`. If there is an obvious “default” version, make an attribute like `json-c = json-c_0_9;`. See also [](#sec-versioning)
228
229## File naming and organisation {#sec-organisation}
230
231Names of files and directories should be in lowercase, with dashes between words — not in camel case. For instance, it should be `all-packages.nix`, not `allPackages.nix` or `AllPackages.nix`.
232
233### Hierarchy {#sec-hierarchy}
234
235Each package should be stored in its own directory somewhere in the `pkgs/` tree, i.e. in `pkgs/category/subcategory/.../pkgname`. Below are some rules for picking the right category for a package. Many packages fall under several categories; what matters is the _primary_ purpose of a package. For example, the `libxml2` package builds both a library and some tools; but it’s a library foremost, so it goes under `pkgs/development/libraries`.
236
237When in doubt, consider refactoring the `pkgs/` tree, e.g. creating new categories or splitting up an existing category.
238
239**If it’s used to support _software development_:**
240
241- **If it’s a _library_ used by other packages:**
242
243 - `development/libraries` (e.g. `libxml2`)
244
245- **If it’s a _compiler_:**
246
247 - `development/compilers` (e.g. `gcc`)
248
249- **If it’s an _interpreter_:**
250
251 - `development/interpreters` (e.g. `guile`)
252
253- **If it’s a (set of) development _tool(s)_:**
254
255 - **If it’s a _parser generator_ (including lexers):**
256
257 - `development/tools/parsing` (e.g. `bison`, `flex`)
258
259 - **If it’s a _build manager_:**
260
261 - `development/tools/build-managers` (e.g. `gnumake`)
262
263 - **Else:**
264
265 - `development/tools/misc` (e.g. `binutils`)
266
267- **Else:**
268
269 - `development/misc`
270
271**If it’s a (set of) _tool(s)_:**
272
273(A tool is a relatively small program, especially one intended to be used non-interactively.)
274
275- **If it’s for _networking_:**
276
277 - `tools/networking` (e.g. `wget`)
278
279- **If it’s for _text processing_:**
280
281 - `tools/text` (e.g. `diffutils`)
282
283- **If it’s a _system utility_, i.e., something related or essential to the operation of a system:**
284
285 - `tools/system` (e.g. `cron`)
286
287- **If it’s an _archiver_ (which may include a compression function):**
288
289 - `tools/archivers` (e.g. `zip`, `tar`)
290
291- **If it’s a _compression_ program:**
292
293 - `tools/compression` (e.g. `gzip`, `bzip2`)
294
295- **If it’s a _security_-related program:**
296
297 - `tools/security` (e.g. `nmap`, `gnupg`)
298
299- **Else:**
300
301 - `tools/misc`
302
303**If it’s a _shell_:**
304
305- `shells` (e.g. `bash`)
306
307**If it’s a _server_:**
308
309- **If it’s a web server:**
310
311 - `servers/http` (e.g. `apache-httpd`)
312
313- **If it’s an implementation of the X Windowing System:**
314
315 - `servers/x11` (e.g. `xorg` — this includes the client libraries and programs)
316
317- **Else:**
318
319 - `servers/misc`
320
321**If it’s a _desktop environment_:**
322
323- `desktops` (e.g. `kde`, `gnome`, `enlightenment`)
324
325**If it’s a _window manager_:**
326
327- `applications/window-managers` (e.g. `awesome`, `stumpwm`)
328
329**If it’s an _application_:**
330
331A (typically large) program with a distinct user interface, primarily used interactively.
332
333- **If it’s a _version management system_:**
334
335 - `applications/version-management` (e.g. `subversion`)
336
337- **If it’s a _terminal emulator_:**
338
339 - `applications/terminal-emulators` (e.g. `alacritty` or `rxvt` or `termite`)
340
341- **If it’s a _file manager_:**
342
343 - `applications/file-managers` (e.g. `mc` or `ranger` or `pcmanfm`)
344
345- **If it’s for _video playback / editing_:**
346
347 - `applications/video` (e.g. `vlc`)
348
349- **If it’s for _graphics viewing / editing_:**
350
351 - `applications/graphics` (e.g. `gimp`)
352
353- **If it’s for _networking_:**
354
355 - **If it’s a _mailreader_:**
356
357 - `applications/networking/mailreaders` (e.g. `thunderbird`)
358
359 - **If it’s a _newsreader_:**
360
361 - `applications/networking/newsreaders` (e.g. `pan`)
362
363 - **If it’s a _web browser_:**
364
365 - `applications/networking/browsers` (e.g. `firefox`)
366
367 - **Else:**
368
369 - `applications/networking/misc`
370
371- **Else:**
372
373 - `applications/misc`
374
375**If it’s _data_ (i.e., does not have a straight-forward executable semantics):**
376
377- **If it’s a _font_:**
378
379 - `data/fonts`
380
381- **If it’s an _icon theme_:**
382
383 - `data/icons`
384
385- **If it’s related to _SGML/XML processing_:**
386
387 - **If it’s an _XML DTD_:**
388
389 - `data/sgml+xml/schemas/xml-dtd` (e.g. `docbook`)
390
391 - **If it’s an _XSLT stylesheet_:**
392
393 (Okay, these are executable...)
394
395 - `data/sgml+xml/stylesheets/xslt` (e.g. `docbook-xsl`)
396
397- **If it’s a _theme_ for a _desktop environment_, a _window manager_ or a _display manager_:**
398
399 - `data/themes`
400
401**If it’s a _game_:**
402
403- `games`
404
405**Else:**
406
407- `misc`
408
409### Versioning {#sec-versioning}
410
411Because every version of a package in Nixpkgs creates a potential maintenance burden, old versions of a package should not be kept unless there is a good reason to do so. For instance, Nixpkgs contains several versions of GCC because other packages don’t build with the latest version of GCC. Other examples are having both the latest stable and latest pre-release version of a package, or to keep several major releases of an application that differ significantly in functionality.
412
413If there is only one version of a package, its Nix expression should be named `e2fsprogs/default.nix`. If there are multiple versions, this should be reflected in the filename, e.g. `e2fsprogs/1.41.8.nix` and `e2fsprogs/1.41.9.nix`. The version in the filename should leave out unnecessary detail. For instance, if we keep the latest Firefox 2.0.x and 3.5.x versions in Nixpkgs, they should be named `firefox/2.0.nix` and `firefox/3.5.nix`, respectively (which, at a given point, might contain versions `2.0.0.20` and `3.5.4`). If a version requires many auxiliary files, you can use a subdirectory for each version, e.g. `firefox/2.0/default.nix` and `firefox/3.5/default.nix`.
414
415All versions of a package _must_ be included in `all-packages.nix` to make sure that they evaluate correctly.
416
417## Fetching Sources {#sec-sources}
418
419There are multiple ways to fetch a package source in nixpkgs. The general guideline is that you should package reproducible sources with a high degree of availability. Right now there is only one fetcher which has mirroring support and that is `fetchurl`. Note that you should also prefer protocols which have a corresponding proxy environment variable.
420
421You can find many source fetch helpers in `pkgs/build-support/fetch*`.
422
423In the file `pkgs/top-level/all-packages.nix` you can find fetch helpers, these have names on the form `fetchFrom*`. The intention of these are to provide snapshot fetches but using the same api as some of the version controlled fetchers from `pkgs/build-support/`. As an example going from bad to good:
424
425- Bad: Uses `git://` which won't be proxied.
426
427 ```nix
428 src = fetchgit {
429 url = "git://github.com/NixOS/nix.git";
430 rev = "1f795f9f44607cc5bec70d1300150bfefcef2aae";
431 sha256 = "1cw5fszffl5pkpa6s6wjnkiv6lm5k618s32sp60kvmvpy7a2v9kg";
432 }
433 ```
434
435- Better: This is ok, but an archive fetch will still be faster.
436
437 ```nix
438 src = fetchgit {
439 url = "https://github.com/NixOS/nix.git";
440 rev = "1f795f9f44607cc5bec70d1300150bfefcef2aae";
441 sha256 = "1cw5fszffl5pkpa6s6wjnkiv6lm5k618s32sp60kvmvpy7a2v9kg";
442 }
443 ```
444
445- Best: Fetches a snapshot archive and you get the rev you want.
446
447 ```nix
448 src = fetchFromGitHub {
449 owner = "NixOS";
450 repo = "nix";
451 rev = "1f795f9f44607cc5bec70d1300150bfefcef2aae";
452 sha256 = "1i2yxndxb6yc9l6c99pypbd92lfq5aac4klq7y2v93c9qvx2cgpc";
453 }
454 ```
455
456When fetching from GitHub, commits must always be referenced by their full commit hash. This is because GitHub shares commit hashes among all forks and returns `404 Not Found` when a short commit hash is ambiguous. It already happens for some short, 6-character commit hashes in `nixpkgs`.
457It is a practical vector for a denial-of-service attack by pushing large amounts of auto generated commits into forks and was already [demonstrated against GitHub Actions Beta](https://blog.teddykatz.com/2019/11/12/github-actions-dos.html).
458
459Find the value to put as `sha256` by running `nix-shell -p nix-prefetch-github --run "nix-prefetch-github --rev 1f795f9f44607cc5bec70d1300150bfefcef2aae NixOS nix"`.
460
461## Obtaining source hash {#sec-source-hashes}
462
463Preferred source hash type is sha256. There are several ways to get it.
464
4651. Prefetch URL (with `nix-prefetch-XXX URL`, where `XXX` is one of `url`, `git`, `hg`, `cvs`, `bzr`, `svn`). Hash is printed to stdout.
466
4672. Prefetch by package source (with `nix-prefetch-url '<nixpkgs>' -A PACKAGE.src`, where `PACKAGE` is package attribute name). Hash is printed to stdout.
468
469 This works well when you've upgraded existing package version and want to find out new hash, but is useless if package can't be accessed by attribute or package has multiple sources (`.srcs`, architecture-dependent sources, etc).
470
4713. Upstream provided hash: use it when upstream provides `sha256` or `sha512` (when upstream provides `md5`, don't use it, compute `sha256` instead).
472
473 A little nuance is that `nix-prefetch-*` tools produce hash encoded with `base32`, but upstream usually provides hexadecimal (`base16`) encoding. Fetchers understand both formats. Nixpkgs does not standardize on any one format.
474
475 You can convert between formats with nix-hash, for example:
476
477 ```ShellSession
478 $ nix-hash --type sha256 --to-base32 HASH
479 ```
480
4814. Extracting hash from local source tarball can be done with `sha256sum`. Use `nix-prefetch-url file:///path/to/tarball` if you want base32 hash.
482
4835. Fake hash: set the hash to one of
484
485 - `""`
486 - `lib.fakeHash`
487 - `lib.fakeSha256`
488 - `lib.fakeSha512`
489
490 in the package expression, attempt build and extract correct hash from error messages.
491
492 ::: {.warning}
493 You must use one of these four fake hashes and not some arbitrarily-chosen hash.
494
495 See [](#sec-source-hashes-security).
496 :::
497
498 This is last resort method when reconstructing source URL is non-trivial and `nix-prefetch-url -A` isn’t applicable (for example, [one of `kodi` dependencies](https://github.com/NixOS/nixpkgs/blob/d2ab091dd308b99e4912b805a5eb088dd536adb9/pkgs/applications/video/kodi/default.nix#L73)). The easiest way then would be replace hash with a fake one and rebuild. Nix build will fail and error message will contain desired hash.
499
500
501### Obtaining hashes securely {#sec-source-hashes-security}
502
503Let's say Man-in-the-Middle (MITM) sits close to your network. Then instead of fetching source you can fetch malware, and instead of source hash you get hash of malware. Here are security considerations for this scenario:
504
505- `http://` URLs are not secure to prefetch hash from;
506
507- hashes from upstream (in method 3) should be obtained via secure protocol;
508
509- `https://` URLs are secure in methods 1, 2, 3;
510
511- `https://` URLs are secure in method 5 *only if* you use one of the listed fake hashes. If you use any other hash, `fetchurl` will pass `--insecure` to `curl` and may then degrade to HTTP in case of TLS certificate expiration.
512
513## Patches {#sec-patches}
514
515Patches available online should be retrieved using `fetchpatch`.
516
517```nix
518patches = [
519 (fetchpatch {
520 name = "fix-check-for-using-shared-freetype-lib.patch";
521 url = "http://git.ghostscript.com/?p=ghostpdl.git;a=patch;h=8f5d285";
522 sha256 = "1f0k043rng7f0rfl9hhb89qzvvksqmkrikmm38p61yfx51l325xr";
523 })
524];
525```
526
527Otherwise, you can add a `.patch` file to the `nixpkgs` repository. In the interest of keeping our maintenance burden to a minimum, only patches that are unique to `nixpkgs` should be added in this way.
528
529If a patch is available online but does not cleanly apply, it can be modified in some fixed ways by using additional optional arguments for `fetchpatch`. Check [](#fetchpatch) for details.
530
531```nix
532patches = [ ./0001-changes.patch ];
533```
534
535If you do need to do create this sort of patch file, one way to do so is with git:
536
5371. Move to the root directory of the source code you're patching.
538
539 ```ShellSession
540 $ cd the/program/source
541 ```
542
5432. If a git repository is not already present, create one and stage all of the source files.
544
545 ```ShellSession
546 $ git init
547 $ git add .
548 ```
549
5503. Edit some files to make whatever changes need to be included in the patch.
551
5524. Use git to create a diff, and pipe the output to a patch file:
553
554 ```ShellSession
555 $ git diff -a > nixpkgs/pkgs/the/package/0001-changes.patch
556 ```
557
558## Package tests {#sec-package-tests}
559
560Tests are important to ensure quality and make reviews and automatic updates easy.
561
562The following types of tests exists:
563
564* [NixOS **module tests**](https://nixos.org/manual/nixos/stable/#sec-nixos-tests), which spawn one or more NixOS VMs. They exercise both NixOS modules and the packaged programs used within them. For example, a NixOS module test can start a web server VM running the `nginx` module, and a client VM running `curl` or a graphical `firefox`, and test that they can talk to each other and display the correct content.
565* Nix **package tests** are a lightweight alternative to NixOS module tests. They should be used to create simple integration tests for packages, but cannot test NixOS services, and some programs with graphical user interfaces may also be difficult to test with them.
566* The **`checkPhase` of a package**, which should execute the unit tests that are included in the source code of a package.
567
568Here in the nixpkgs manual we describe mostly _package tests_; for _module tests_ head over to the corresponding [section in the NixOS manual](https://nixos.org/manual/nixos/stable/#sec-nixos-tests).
569
570### Writing inline package tests {#ssec-inline-package-tests-writing}
571
572For very simple tests, they can be written inline:
573
574```nix
575{ …, yq-go }:
576
577buildGoModule rec {
578 …
579
580 passthru.tests = {
581 simple = runCommand "${pname}-test" {} ''
582 echo "test: 1" | ${yq-go}/bin/yq eval -j > $out
583 [ "$(cat $out | tr -d $'\n ')" = '{"test":1}' ]
584 '';
585 };
586}
587```
588
589### Writing larger package tests {#ssec-package-tests-writing}
590
591This is an example using the `phoronix-test-suite` package with the current best practices.
592
593Add the tests in `passthru.tests` to the package definition like this:
594
595```nix
596{ stdenv, lib, fetchurl, callPackage }:
597
598stdenv.mkDerivation {
599 …
600
601 passthru.tests = {
602 simple-execution = callPackage ./tests.nix { };
603 };
604
605 meta = { … };
606}
607```
608
609Create `tests.nix` in the package directory:
610
611```nix
612{ runCommand, phoronix-test-suite }:
613
614let
615 inherit (phoronix-test-suite) pname version;
616in
617
618runCommand "${pname}-tests" { meta.timeout = 60; }
619 ''
620 # automatic initial setup to prevent interactive questions
621 ${phoronix-test-suite}/bin/phoronix-test-suite enterprise-setup >/dev/null
622 # get version of installed program and compare with package version
623 if [[ `${phoronix-test-suite}/bin/phoronix-test-suite version` != *"${version}"* ]]; then
624 echo "Error: program version does not match package version"
625 exit 1
626 fi
627 # run dummy command
628 ${phoronix-test-suite}/bin/phoronix-test-suite dummy_module.dummy-command >/dev/null
629 # needed for Nix to register the command as successful
630 touch $out
631 ''
632```
633
634### Running package tests {#ssec-package-tests-running}
635
636You can run these tests with:
637
638```ShellSession
639$ cd path/to/nixpkgs
640$ nix-build -A phoronix-test-suite.tests
641```
642
643### Examples of package tests {#ssec-package-tests-examples}
644
645Here are examples of package tests:
646
647- [Jasmin compile test](https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/compilers/jasmin/test-assemble-hello-world/default.nix)
648- [Lobster compile test](https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/compilers/lobster/test-can-run-hello-world.nix)
649- [Spacy annotation test](https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/python-modules/spacy/annotation-test/default.nix)
650- [Libtorch test](https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/libraries/science/math/libtorch/test/default.nix)
651- [Multiple tests for nanopb](https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/libraries/nanopb/default.nix)
652
653### Linking NixOS module tests to a package {#ssec-nixos-tests-linking}
654
655Like [package tests](#ssec-package-tests-writing) as shown above, [NixOS module tests](https://nixos.org/manual/nixos/stable/#sec-nixos-tests) can also be linked to a package, so that the tests can be easily run when changing the related package.
656
657For example, assuming we're packaging `nginx`, we can link its module test via `passthru.tests`:
658
659```nix
660{ stdenv, lib, nixosTests }:
661
662stdenv.mkDerivation {
663 ...
664
665 passthru.tests = {
666 nginx = nixosTests.nginx;
667 };
668
669 ...
670}
671```