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 <xref linkend="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- Arguments should be listed in the order they are used, with the exception of `lib`, which always goes first.
185
186- The top-level `lib` must be used in the master and 21.05 branch over its alias `stdenv.lib` as it now causes evaluation errors when aliases are disabled which is the case for ofborg.
187 `lib` is unrelated to `stdenv`, and so `stdenv.lib` should only be used as a convenience alias when developing locally to avoid having to modify the function inputs just to test something out.
188
189## Package naming {#sec-package-naming}
190
191The 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.
192
193In Nixpkgs, there are generally three different names associated with a package:
194
195- The `name` attribute of the derivation (excluding the version part). This is what most users see, in particular when using `nix-env`.
196
197- 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`.
198
199- The filename for (the directory containing) the Nix expression.
200
201Most 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`.
202
203There are a few naming guidelines:
204
205- The `name` attribute _should_ be identical to the upstream package name.
206
207- The `name` attribute _must not_ contain uppercase letters — e.g., `"mplayer-1.0rc2"` instead of `"MPlayer-1.0rc2"`.
208
209- The version part of the `name` attribute _must_ start with a digit (following a dash) — e.g., `"hello-0.3.1rc2"`.
210
211- If a package is not a release but a commit from a repository, then the version part of the name _must_ be the date of that (fetched) commit. The date _must_ be in `"YYYY-MM-DD"` format. Also append `"unstable"` to the name - e.g., `"pkgname-unstable-2014-09-23"`.
212
213- Dashes in the package name _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.
214
215- 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 <xref linkend="sec-versioning" />
216
217## File naming and organisation {#sec-organisation}
218
219Names 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`.
220
221### Hierarchy {#sec-hierarchy}
222
223Each 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`.
224
225When in doubt, consider refactoring the `pkgs/` tree, e.g. creating new categories or splitting up an existing category.
226
227**If it’s used to support _software development_:**
228
229- **If it’s a _library_ used by other packages:**
230
231 - `development/libraries` (e.g. `libxml2`)
232
233- **If it’s a _compiler_:**
234
235 - `development/compilers` (e.g. `gcc`)
236
237- **If it’s an _interpreter_:**
238
239 - `development/interpreters` (e.g. `guile`)
240
241- **If it’s a (set of) development _tool(s)_:**
242
243 - **If it’s a _parser generator_ (including lexers):**
244
245 - `development/tools/parsing` (e.g. `bison`, `flex`)
246
247 - **If it’s a _build manager_:**
248
249 - `development/tools/build-managers` (e.g. `gnumake`)
250
251 - **Else:**
252
253 - `development/tools/misc` (e.g. `binutils`)
254
255- **Else:**
256
257 - `development/misc`
258
259**If it’s a (set of) _tool(s)_:**
260
261(A tool is a relatively small program, especially one intended to be used non-interactively.)
262
263- **If it’s for _networking_:**
264
265 - `tools/networking` (e.g. `wget`)
266
267- **If it’s for _text processing_:**
268
269 - `tools/text` (e.g. `diffutils`)
270
271- **If it’s a _system utility_, i.e., something related or essential to the operation of a system:**
272
273 - `tools/system` (e.g. `cron`)
274
275- **If it’s an _archiver_ (which may include a compression function):**
276
277 - `tools/archivers` (e.g. `zip`, `tar`)
278
279- **If it’s a _compression_ program:**
280
281 - `tools/compression` (e.g. `gzip`, `bzip2`)
282
283- **If it’s a _security_-related program:**
284
285 - `tools/security` (e.g. `nmap`, `gnupg`)
286
287- **Else:**
288
289 - `tools/misc`
290
291**If it’s a _shell_:**
292
293- `shells` (e.g. `bash`)
294
295**If it’s a _server_:**
296
297- **If it’s a web server:**
298
299 - `servers/http` (e.g. `apache-httpd`)
300
301- **If it’s an implementation of the X Windowing System:**
302
303 - `servers/x11` (e.g. `xorg` — this includes the client libraries and programs)
304
305- **Else:**
306
307 - `servers/misc`
308
309**If it’s a _desktop environment_:**
310
311- `desktops` (e.g. `kde`, `gnome`, `enlightenment`)
312
313**If it’s a _window manager_:**
314
315- `applications/window-managers` (e.g. `awesome`, `stumpwm`)
316
317**If it’s an _application_:**
318
319A (typically large) program with a distinct user interface, primarily used interactively.
320
321- **If it’s a _version management system_:**
322
323 - `applications/version-management` (e.g. `subversion`)
324
325- **If it’s a _terminal emulator_:**
326
327 - `applications/terminal-emulators` (e.g. `alacritty` or `rxvt` or `termite`)
328
329- **If it’s for _video playback / editing_:**
330
331 - `applications/video` (e.g. `vlc`)
332
333- **If it’s for _graphics viewing / editing_:**
334
335 - `applications/graphics` (e.g. `gimp`)
336
337- **If it’s for _networking_:**
338
339 - **If it’s a _mailreader_:**
340
341 - `applications/networking/mailreaders` (e.g. `thunderbird`)
342
343 - **If it’s a _newsreader_:**
344
345 - `applications/networking/newsreaders` (e.g. `pan`)
346
347 - **If it’s a _web browser_:**
348
349 - `applications/networking/browsers` (e.g. `firefox`)
350
351 - **Else:**
352
353 - `applications/networking/misc`
354
355- **Else:**
356
357 - `applications/misc`
358
359**If it’s _data_ (i.e., does not have a straight-forward executable semantics):**
360
361- **If it’s a _font_:**
362
363 - `data/fonts`
364
365- **If it’s an _icon theme_:**
366
367 - `data/icons`
368
369- **If it’s related to _SGML/XML processing_:**
370
371 - **If it’s an _XML DTD_:**
372
373 - `data/sgml+xml/schemas/xml-dtd` (e.g. `docbook`)
374
375 - **If it’s an _XSLT stylesheet_:**
376
377 (Okay, these are executable...)
378
379 - `data/sgml+xml/stylesheets/xslt` (e.g. `docbook-xsl`)
380
381- **If it’s a _theme_ for a _desktop environment_, a _window manager_ or a _display manager_:**
382
383 - `data/themes`
384
385**If it’s a _game_:**
386
387- `games`
388
389**Else:**
390
391- `misc`
392
393### Versioning {#sec-versioning}
394
395Because 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.
396
397If 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`.
398
399All versions of a package _must_ be included in `all-packages.nix` to make sure that they evaluate correctly.
400
401## Fetching Sources {#sec-sources}
402
403There 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.
404
405You can find many source fetch helpers in `pkgs/build-support/fetch*`.
406
407In 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:
408
409- Bad: Uses `git://` which won't be proxied.
410
411 ```nix
412 src = fetchgit {
413 url = "git://github.com/NixOS/nix.git";
414 rev = "1f795f9f44607cc5bec70d1300150bfefcef2aae";
415 sha256 = "1cw5fszffl5pkpa6s6wjnkiv6lm5k618s32sp60kvmvpy7a2v9kg";
416 }
417 ```
418
419- Better: This is ok, but an archive fetch will still be faster.
420
421 ```nix
422 src = fetchgit {
423 url = "https://github.com/NixOS/nix.git";
424 rev = "1f795f9f44607cc5bec70d1300150bfefcef2aae";
425 sha256 = "1cw5fszffl5pkpa6s6wjnkiv6lm5k618s32sp60kvmvpy7a2v9kg";
426 }
427 ```
428
429- Best: Fetches a snapshot archive and you get the rev you want.
430
431 ```nix
432 src = fetchFromGitHub {
433 owner = "NixOS";
434 repo = "nix";
435 rev = "1f795f9f44607cc5bec70d1300150bfefcef2aae";
436 sha256 = "1i2yxndxb6yc9l6c99pypbd92lfq5aac4klq7y2v93c9qvx2cgpc";
437 }
438 ```
439
440 Find the value to put as `sha256` by running `nix run -f '<nixpkgs>' nix-prefetch-github -c nix-prefetch-github --rev 1f795f9f44607cc5bec70d1300150bfefcef2aae NixOS nix` or `nix-prefetch-url --unpack https://github.com/NixOS/nix/archive/1f795f9f44607cc5bec70d1300150bfefcef2aae.tar.gz`.
441
442## Obtaining source hash {#sec-source-hashes}
443
444Preferred source hash type is sha256. There are several ways to get it.
445
4461. Prefetch URL (with `nix-prefetch-XXX URL`, where `XXX` is one of `url`, `git`, `hg`, `cvs`, `bzr`, `svn`). Hash is printed to stdout.
447
4482. Prefetch by package source (with `nix-prefetch-url '<nixpkgs>' -A PACKAGE.src`, where `PACKAGE` is package attribute name). Hash is printed to stdout.
449
450 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).
451
4523. Upstream provided hash: use it when upstream provides `sha256` or `sha512` (when upstream provides `md5`, don't use it, compute `sha256` instead).
453
454 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.
455
456 You can convert between formats with nix-hash, for example:
457
458 ```ShellSession
459 $ nix-hash --type sha256 --to-base32 HASH
460 ```
461
4624. Extracting hash from local source tarball can be done with `sha256sum`. Use `nix-prefetch-url file:///path/to/tarball` if you want base32 hash.
463
4645. Fake hash: set fake hash in package expression, perform build and extract correct hash from error Nix prints.
465
466 For package updates it is enough to change one symbol to make hash fake. For new packages, you can use `lib.fakeSha256`, `lib.fakeSha512` or any other fake hash.
467
468 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.
469
470::: warning
471This method has security problems. Check below for details.
472:::
473
474### Obtaining hashes securely {#sec-source-hashes-security}
475
476Let'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:
477
478- `http://` URLs are not secure to prefetch hash from;
479
480- hashes from upstream (in method 3) should be obtained via secure protocol;
481
482- `https://` URLs are secure in methods 1, 2, 3;
483
484- `https://` URLs are not secure in method 5. When obtaining hashes with fake hash method, TLS checks are disabled. So refetch source hash from several different networks to exclude MITM scenario. Alternatively, use fake hash method to make Nix error, but instead of extracting hash from error, extract `https://` URL and prefetch it with method 1.
485
486## Patches {#sec-patches}
487
488Patches available online should be retrieved using `fetchpatch`.
489
490```nix
491patches = [
492 (fetchpatch {
493 name = "fix-check-for-using-shared-freetype-lib.patch";
494 url = "http://git.ghostscript.com/?p=ghostpdl.git;a=patch;h=8f5d285";
495 sha256 = "1f0k043rng7f0rfl9hhb89qzvvksqmkrikmm38p61yfx51l325xr";
496 })
497];
498```
499
500Otherwise, 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.
501
502```nix
503patches = [ ./0001-changes.patch ];
504```
505
506If you do need to do create this sort of patch file, one way to do so is with git:
507
5081. Move to the root directory of the source code you're patching.
509
510 ```ShellSession
511 $ cd the/program/source
512 ```
513
5142. If a git repository is not already present, create one and stage all of the source files.
515
516 ```ShellSession
517 $ git init
518 $ git add .
519 ```
520
5213. Edit some files to make whatever changes need to be included in the patch.
522
5234. Use git to create a diff, and pipe the output to a patch file:
524
525 ```ShellSession
526 $ git diff > nixpkgs/pkgs/the/package/0001-changes.patch
527 ```
528
529## Package tests {#sec-package-tests}
530
531Tests are important to ensure quality and make reviews and automatic updates easy.
532
533Nix package tests are a lightweight alternative to [NixOS module tests](https://nixos.org/manual/nixos/stable/#sec-nixos-tests). They can be used to create simple integration tests for packages while the module tests are used to test services or programs with a graphical user interface on a NixOS VM. Unittests that are included in the source code of a package should be executed in the `checkPhase`.
534
535### Writing package tests {#ssec-package-tests-writing}
536
537This is an example using the `phoronix-test-suite` package with the current best practices.
538
539Add the tests in `passthru.tests` to the package definition like this:
540
541```nix
542{ stdenv, lib, fetchurl, callPackage }:
543
544stdenv.mkDerivation {
545 …
546
547 passthru.tests = {
548 simple-execution = callPackage ./tests.nix { };
549 };
550
551 meta = { … };
552}
553```
554
555Create `tests.nix` in the package directory:
556
557```nix
558{ runCommand, phoronix-test-suite }:
559
560let
561 inherit (phoronix-test-suite) pname version;
562in
563
564runCommand "${pname}-tests" { meta.timeout = 3; }
565 ''
566 # automatic initial setup to prevent interactive questions
567 ${phoronix-test-suite}/bin/phoronix-test-suite enterprise-setup >/dev/null
568 # get version of installed program and compare with package version
569 if [[ `${phoronix-test-suite}/bin/phoronix-test-suite version` != *"${version}"* ]]; then
570 echo "Error: program version does not match package version"
571 exit 1
572 fi
573 # run dummy command
574 ${phoronix-test-suite}/bin/phoronix-test-suite dummy_module.dummy-command >/dev/null
575 # needed for Nix to register the command as successful
576 touch $out
577 ''
578```
579
580### Running package tests {#ssec-package-tests-running}
581
582You can run these tests with:
583
584```ShellSession
585$ cd path/to/nixpkgs
586$ nix-build -A phoronix-test-suite.tests
587```
588
589### Examples of package tests {#ssec-package-tests-examples}
590
591Here are examples of package tests:
592
593- [Jasmin compile test](https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/compilers/jasmin/test-assemble-hello-world/default.nix)
594- [Lobster compile test](https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/compilers/lobster/test-can-run-hello-world.nix)
595- [Spacy annotation test](https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/python-modules/spacy/annotation-test/default.nix)
596- [Libtorch test](https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/libraries/science/math/libtorch/test/default.nix)
597- [Multiple tests for nanopb](https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/libraries/nanopb/default.nix)