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diff --git a/doc/contributing.texi b/doc/contributing.texi index f24886233d..ecc20dabc5 100644 --- a/doc/contributing.texi +++ b/doc/contributing.texi @@ -23,6 +23,7 @@ choice. * Building from Git:: The latest and greatest. * Running Guix Before It Is Installed:: Hacker tricks. * The Perfect Setup:: The right tools. +* Packaging Guidelines:: Growing the distribution. * Coding Style:: Hygiene of the contributor. * Submitting Patches:: Share your work. @end menu @@ -223,6 +224,455 @@ trigger string @code{origin...}, which can be expanded further. The @code{...}, which also can be expanded further. +@node Packaging Guidelines +@section Packaging Guidelines + +@cindex packages, creating +The GNU distribution is nascent and may well lack some of your favorite +packages. This section describes how you can help make the distribution +grow. + +Free software packages are usually distributed in the form of +@dfn{source code tarballs}---typically @file{tar.gz} files that contain +all the source files. Adding a package to the distribution means +essentially two things: adding a @dfn{recipe} that describes how to +build the package, including a list of other packages required to build +it, and adding @dfn{package metadata} along with that recipe, such as a +description and licensing information. + +In Guix all this information is embodied in @dfn{package definitions}. +Package definitions provide a high-level view of the package. They are +written using the syntax of the Scheme programming language; in fact, +for each package we define a variable bound to the package definition, +and export that variable from a module (@pxref{Package Modules}). +However, in-depth Scheme knowledge is @emph{not} a prerequisite for +creating packages. For more information on package definitions, +@pxref{Defining Packages}. + +Once a package definition is in place, stored in a file in the Guix +source tree, it can be tested using the @command{guix build} command +(@pxref{Invoking guix build}). For example, assuming the new package is +called @code{gnew}, you may run this command from the Guix build tree +(@pxref{Running Guix Before It Is Installed}): + +@example +./pre-inst-env guix build gnew --keep-failed +@end example + +Using @code{--keep-failed} makes it easier to debug build failures since +it provides access to the failed build tree. Another useful +command-line option when debugging is @code{--log-file}, to access the +build log. + +If the package is unknown to the @command{guix} command, it may be that +the source file contains a syntax error, or lacks a @code{define-public} +clause to export the package variable. To figure it out, you may load +the module from Guile to get more information about the actual error: + +@example +./pre-inst-env guile -c '(use-modules (gnu packages gnew))' +@end example + +Once your package builds correctly, please send us a patch +(@pxref{Submitting Patches}). Well, if you need help, we will be happy to +help you too. Once the patch is committed in the Guix repository, the +new package automatically gets built on the supported platforms by +@url{http://hydra.gnu.org/jobset/gnu/master, our continuous integration +system}. + +@cindex substituter +Users can obtain the new package definition simply by running +@command{guix pull} (@pxref{Invoking guix pull}). When +@code{@value{SUBSTITUTE-SERVER}} is done building the package, installing the +package automatically downloads binaries from there +(@pxref{Substitutes}). The only place where human intervention is +needed is to review and apply the patch. + + +@menu +* Software Freedom:: What may go into the distribution. +* Package Naming:: What's in a name? +* Version Numbers:: When the name is not enough. +* Synopses and Descriptions:: Helping users find the right package. +* Python Modules:: A touch of British comedy. +* Perl Modules:: Little pearls. +* Java Packages:: Coffee break. +* Fonts:: Fond of fonts. +@end menu + +@node Software Freedom +@subsection Software Freedom + +@c Adapted from http://www.gnu.org/philosophy/philosophy.html. +@cindex free software +The GNU operating system has been developed so that users can have +freedom in their computing. GNU is @dfn{free software}, meaning that +users have the @url{http://www.gnu.org/philosophy/free-sw.html,four +essential freedoms}: to run the program, to study and change the program +in source code form, to redistribute exact copies, and to distribute +modified versions. Packages found in the GNU distribution provide only +software that conveys these four freedoms. + +In addition, the GNU distribution follow the +@url{http://www.gnu.org/distros/free-system-distribution-guidelines.html,free +software distribution guidelines}. Among other things, these guidelines +reject non-free firmware, recommendations of non-free software, and +discuss ways to deal with trademarks and patents. + +Some otherwise free upstream package sources contain a small and optional +subset that violates the above guidelines, for instance because this subset +is itself non-free code. When that happens, the offending items are removed +with appropriate patches or code snippets in the @code{origin} form of the +package (@pxref{Defining Packages}). This way, @code{guix +build --source} returns the ``freed'' source rather than the unmodified +upstream source. + + +@node Package Naming +@subsection Package Naming + +@cindex package name +A package has actually two names associated with it: +First, there is the name of the @emph{Scheme variable}, the one following +@code{define-public}. By this name, the package can be made known in the +Scheme code, for instance as input to another package. Second, there is +the string in the @code{name} field of a package definition. This name +is used by package management commands such as +@command{guix package} and @command{guix build}. + +Both are usually the same and correspond to the lowercase conversion of +the project name chosen upstream, with underscores replaced with +hyphens. For instance, GNUnet is available as @code{gnunet}, and +SDL_net as @code{sdl-net}. + +We do not add @code{lib} prefixes for library packages, unless these are +already part of the official project name. But @pxref{Python +Modules} and @ref{Perl Modules} for special rules concerning modules for +the Python and Perl languages. + +Font package names are handled differently, @pxref{Fonts}. + + +@node Version Numbers +@subsection Version Numbers + +@cindex package version +We usually package only the latest version of a given free software +project. But sometimes, for instance for incompatible library versions, +two (or more) versions of the same package are needed. These require +different Scheme variable names. We use the name as defined +in @ref{Package Naming} +for the most recent version; previous versions use the same name, suffixed +by @code{-} and the smallest prefix of the version number that may +distinguish the two versions. + +The name inside the package definition is the same for all versions of a +package and does not contain any version number. + +For instance, the versions 2.24.20 and 3.9.12 of GTK+ may be packaged as follows: + +@example +(define-public gtk+ + (package + (name "gtk+") + (version "3.9.12") + ...)) +(define-public gtk+-2 + (package + (name "gtk+") + (version "2.24.20") + ...)) +@end example +If we also wanted GTK+ 3.8.2, this would be packaged as +@example +(define-public gtk+-3.8 + (package + (name "gtk+") + (version "3.8.2") + ...)) +@end example + +@c See <https://lists.gnu.org/archive/html/guix-devel/2016-01/msg00425.html>, +@c for a discussion of what follows. +@cindex version number, for VCS snapshots +Occasionally, we package snapshots of upstream's version control system +(VCS) instead of formal releases. This should remain exceptional, +because it is up to upstream developers to clarify what the stable +release is. Yet, it is sometimes necessary. So, what should we put in +the @code{version} field? + +Clearly, we need to make the commit identifier of the VCS snapshot +visible in the version string, but we also need to make sure that the +version string is monotonically increasing so that @command{guix package +--upgrade} can determine which version is newer. Since commit +identifiers, notably with Git, are not monotonically increasing, we add +a revision number that we increase each time we upgrade to a newer +snapshot. The resulting version string looks like this: + +@example +2.0.11-3.cabba9e + ^ ^ ^ + | | `-- upstream commit ID + | | + | `--- Guix package revision + | +latest upstream version +@end example + +It is a good idea to strip commit identifiers in the @code{version} +field to, say, 7 digits. It avoids an aesthetic annoyance (assuming +aesthetics have a role to play here) as well as problems related to OS +limits such as the maximum shebang length (127 bytes for the Linux +kernel.) It is best to use the full commit identifiers in +@code{origin}s, though, to avoid ambiguities. A typical package +definition may look like this: + +@example +(define my-package + (let ((commit "c3f29bc928d5900971f65965feaae59e1272a3f7") + (revision "1")) ;Guix package revision + (package + (version (git-version "0.9" revision commit)) + (source (origin + (method git-fetch) + (uri (git-reference + (url "git://example.org/my-package.git") + (commit commit))) + (sha256 (base32 "1mbikn@dots{}")) + (file-name (git-file-name name version)))) + ;; @dots{} + ))) +@end example + +@node Synopses and Descriptions +@subsection Synopses and Descriptions + +@cindex package description +@cindex package synopsis +As we have seen before, each package in GNU@tie{}Guix includes a +synopsis and a description (@pxref{Defining Packages}). Synopses and +descriptions are important: They are what @command{guix package +--search} searches, and a crucial piece of information to help users +determine whether a given package suits their needs. Consequently, +packagers should pay attention to what goes into them. + +Synopses must start with a capital letter and must not end with a +period. They must not start with ``a'' or ``the'', which usually does +not bring anything; for instance, prefer ``File-frobbing tool'' over ``A +tool that frobs files''. The synopsis should say what the package +is---e.g., ``Core GNU utilities (file, text, shell)''---or what it is +used for---e.g., the synopsis for GNU@tie{}grep is ``Print lines +matching a pattern''. + +Keep in mind that the synopsis must be meaningful for a very wide +audience. For example, ``Manipulate alignments in the SAM format'' +might make sense for a seasoned bioinformatics researcher, but might be +fairly unhelpful or even misleading to a non-specialized audience. It +is a good idea to come up with a synopsis that gives an idea of the +application domain of the package. In this example, this might give +something like ``Manipulate nucleotide sequence alignments'', which +hopefully gives the user a better idea of whether this is what they are +looking for. + +Descriptions should take between five and ten lines. Use full +sentences, and avoid using acronyms without first introducing them. +Please avoid marketing phrases such as ``world-leading'', +``industrial-strength'', and ``next-generation'', and avoid superlatives +like ``the most advanced''---they are not helpful to users looking for a +package and may even sound suspicious. Instead, try to be factual, +mentioning use cases and features. + +@cindex Texinfo markup, in package descriptions +Descriptions can include Texinfo markup, which is useful to introduce +ornaments such as @code{@@code} or @code{@@dfn}, bullet lists, or +hyperlinks (@pxref{Overview,,, texinfo, GNU Texinfo}). However you +should be careful when using some characters for example @samp{@@} and +curly braces which are the basic special characters in Texinfo +(@pxref{Special Characters,,, texinfo, GNU Texinfo}). User interfaces +such as @command{guix package --show} take care of rendering it +appropriately. + +Synopses and descriptions are translated by volunteers +@uref{http://translationproject.org/domain/guix-packages.html, at the +Translation Project} so that as many users as possible can read them in +their native language. User interfaces search them and display them in +the language specified by the current locale. + +To allow @command{xgettext} to extract them as translatable strings, +synopses and descriptions @emph{must be literal strings}. This means +that you cannot use @code{string-append} or @code{format} to construct +these strings: + +@lisp +(package + ;; @dots{} + (synopsis "This is translatable") + (description (string-append "This is " "*not*" " translatable."))) +@end lisp + +Translation is a lot of work so, as a packager, please pay even more +attention to your synopses and descriptions as every change may entail +additional work for translators. In order to help them, it is possible +to make recommendations or instructions visible to them by inserting +special comments like this (@pxref{xgettext Invocation,,, gettext, GNU +Gettext}): + +@example +;; TRANSLATORS: "X11 resize-and-rotate" should not be translated. +(description "ARandR is designed to provide a simple visual front end +for the X11 resize-and-rotate (RandR) extension. @dots{}") +@end example + + +@node Python Modules +@subsection Python Modules + +@cindex python +We currently package Python 2 and Python 3, under the Scheme variable names +@code{python-2} and @code{python} as explained in @ref{Version Numbers}. +To avoid confusion and naming clashes with other programming languages, it +seems desirable that the name of a package for a Python module contains +the word @code{python}. + +Some modules are compatible with only one version of Python, others with both. +If the package Foo compiles only with Python 3, we name it +@code{python-foo}; if it compiles only with Python 2, we name it +@code{python2-foo}. If it is compatible with both versions, we create two +packages with the corresponding names. + +If a project already contains the word @code{python}, we drop this; +for instance, the module python-dateutil is packaged under the names +@code{python-dateutil} and @code{python2-dateutil}. If the project name +starts with @code{py} (e.g.@: @code{pytz}), we keep it and prefix it as +described above. + +@subsubsection Specifying Dependencies +@cindex inputs, for Python packages + +Dependency information for Python packages is usually available in the +package source tree, with varying degrees of accuracy: in the +@file{setup.py} file, in @file{requirements.txt}, or in @file{tox.ini}. + +Your mission, when writing a recipe for a Python package, is to map +these dependencies to the appropriate type of ``input'' (@pxref{package +Reference, inputs}). Although the @code{pypi} importer normally does a +good job (@pxref{Invoking guix import}), you may want to check the +following check list to determine which dependency goes where. + +@itemize + +@item +We currently package Python 2 with @code{setuptools} and @code{pip} +installed like Python 3.4 has per default. Thus you don't need to +specify either of these as an input. @command{guix lint} will warn you +if you do. + +@item +Python dependencies required at run time go into +@code{propagated-inputs}. They are typically defined with the +@code{install_requires} keyword in @file{setup.py}, or in the +@file{requirements.txt} file. + +@item +Python packages required only at build time---e.g., those listed with +the @code{setup_requires} keyword in @file{setup.py}---or only for +testing---e.g., those in @code{tests_require}---go into +@code{native-inputs}. The rationale is that (1) they do not need to be +propagated because they are not needed at run time, and (2) in a +cross-compilation context, it's the ``native'' input that we'd want. + +Examples are the @code{pytest}, @code{mock}, and @code{nose} test +frameworks. Of course if any of these packages is also required at +run-time, it needs to go to @code{propagated-inputs}. + +@item +Anything that does not fall in the previous categories goes to +@code{inputs}, for example programs or C libraries required for building +Python packages containing C extensions. + +@item +If a Python package has optional dependencies (@code{extras_require}), +it is up to you to decide whether to add them or not, based on their +usefulness/overhead ratio (@pxref{Submitting Patches, @command{guix +size}}). + +@end itemize + + +@node Perl Modules +@subsection Perl Modules + +@cindex perl +Perl programs standing for themselves are named as any other package, +using the lowercase upstream name. +For Perl packages containing a single class, we use the lowercase class name, +replace all occurrences of @code{::} by dashes and prepend the prefix +@code{perl-}. +So the class @code{XML::Parser} becomes @code{perl-xml-parser}. +Modules containing several classes keep their lowercase upstream name and +are also prepended by @code{perl-}. Such modules tend to have the word +@code{perl} somewhere in their name, which gets dropped in favor of the +prefix. For instance, @code{libwww-perl} becomes @code{perl-libwww}. + + +@node Java Packages +@subsection Java Packages + +@cindex java +Java programs standing for themselves are named as any other package, +using the lowercase upstream name. + +To avoid confusion and naming clashes with other programming languages, +it is desirable that the name of a package for a Java package is +prefixed with @code{java-}. If a project already contains the word +@code{java}, we drop this; for instance, the package @code{ngsjava} is +packaged under the name @code{java-ngs}. + +For Java packages containing a single class or a small class hierarchy, +we use the lowercase class name, replace all occurrences of @code{.} by +dashes and prepend the prefix @code{java-}. So the class +@code{apache.commons.cli} becomes package +@code{java-apache-commons-cli}. + + +@node Fonts +@subsection Fonts + +@cindex fonts +For fonts that are in general not installed by a user for typesetting +purposes, or that are distributed as part of a larger software package, +we rely on the general packaging rules for software; for instance, this +applies to the fonts delivered as part of the X.Org system or fonts that +are part of TeX Live. + +To make it easier for a user to search for fonts, names for other packages +containing only fonts are constructed as follows, independently of the +upstream package name. + +The name of a package containing only one font family starts with +@code{font-}; it is followed by the foundry name and a dash @code{-} +if the foundry is known, and the font family name, in which spaces are +replaced by dashes (and as usual, all upper case letters are transformed +to lower case). +For example, the Gentium font family by SIL is packaged under the name +@code{font-sil-gentium}. + +For a package containing several font families, the name of the collection +is used in the place of the font family name. +For instance, the Liberation fonts consist of three families, +Liberation Sans, Liberation Serif and Liberation Mono. +These could be packaged separately under the names +@code{font-liberation-sans} and so on; but as they are distributed together +under a common name, we prefer to package them together as +@code{font-liberation}. + +In the case where several formats of the same font family or font collection +are packaged separately, a short form of the format, prepended by a dash, +is added to the package name. We use @code{-ttf} for TrueType fonts, +@code{-otf} for OpenType fonts and @code{-type1} for PostScript Type 1 +fonts. + + @node Coding Style @section Coding Style |