666 lines
22 KiB
XML
666 lines
22 KiB
XML
<chapter xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xml:id="chap-conventions">
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<title>Coding conventions</title>
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<section xml:id="sec-syntax"><title>Syntax</title>
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<itemizedlist>
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<listitem><para>Use 2 spaces of indentation per indentation level in
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Nix expressions, 4 spaces in shell scripts.</para></listitem>
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<listitem><para>Do not use tab characters, i.e. configure your
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editor to use soft tabs. For instance, use <literal>(setq-default
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indent-tabs-mode nil)</literal> in Emacs. Everybody has different
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tab settings so it’s asking for trouble.</para></listitem>
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<listitem><para>Use <literal>lowerCamelCase</literal> for variable
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names, not <literal>UpperCamelCase</literal>. TODO: naming of
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attributes in
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<filename>all-packages.nix</filename>?</para></listitem>
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<listitem><para>Function calls with attribute set arguments are
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written as
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<programlisting>
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foo {
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arg = ...;
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}
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</programlisting>
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not
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<programlisting>
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foo
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{
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arg = ...;
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}
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</programlisting>
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Also fine is
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<programlisting>
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foo { arg = ...; }
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</programlisting>
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if it's a short call.</para></listitem>
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<listitem><para>In attribute sets or lists that span multiple lines,
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the attribute names or list elements should be aligned:
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<programlisting>
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# A long list.
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list =
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[ elem1
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elem2
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elem3
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];
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# A long attribute set.
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attrs =
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{ attr1 = short_expr;
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attr2 =
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if true then big_expr else big_expr;
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};
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# Alternatively:
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attrs = {
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attr1 = short_expr;
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attr2 =
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if true then big_expr else big_expr;
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};
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</programlisting>
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</para></listitem>
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<listitem><para>Short lists or attribute sets can be written on one
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line:
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<programlisting>
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# A short list.
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list = [ elem1 elem2 elem3 ];
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# A short set.
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attrs = { x = 1280; y = 1024; };
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</programlisting>
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</para></listitem>
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<listitem><para>Breaking in the middle of a function argument can
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give hard-to-read code, like
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<programlisting>
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someFunction { x = 1280;
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y = 1024; } otherArg
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yetAnotherArg
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</programlisting>
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(especially if the argument is very large, spanning multiple
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lines).</para>
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<para>Better:
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<programlisting>
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someFunction
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{ x = 1280; y = 1024; }
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otherArg
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yetAnotherArg
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</programlisting>
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or
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<programlisting>
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let res = { x = 1280; y = 1024; };
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in someFunction res otherArg yetAnotherArg
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</programlisting>
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</para></listitem>
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<listitem><para>The bodies of functions, asserts, and withs are not
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indented to prevent a lot of superfluous indentation levels, i.e.
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<programlisting>
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{ arg1, arg2 }:
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assert system == "i686-linux";
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stdenv.mkDerivation { ...
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</programlisting>
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not
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<programlisting>
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{ arg1, arg2 }:
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assert system == "i686-linux";
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stdenv.mkDerivation { ...
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</programlisting>
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</para></listitem>
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<listitem><para>Function formal arguments are written as:
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<programlisting>
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{ arg1, arg2, arg3 }:
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</programlisting>
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but if they don't fit on one line they're written as:
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<programlisting>
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{ arg1, arg2, arg3
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, arg4, ...
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, # Some comment...
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argN
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}:
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</programlisting>
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</para></listitem>
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<listitem><para>Functions should list their expected arguments as
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precisely as possible. That is, write
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<programlisting>
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{ stdenv, fetchurl, perl }: <replaceable>...</replaceable>
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</programlisting>
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instead of
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<programlisting>
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args: with args; <replaceable>...</replaceable>
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</programlisting>
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or
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<programlisting>
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{ stdenv, fetchurl, perl, ... }: <replaceable>...</replaceable>
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</programlisting>
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</para>
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<para>For functions that are truly generic in the number of
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arguments (such as wrappers around <varname>mkDerivation</varname>)
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that have some required arguments, you should write them using an
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<literal>@</literal>-pattern:
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<programlisting>
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{ stdenv, doCoverageAnalysis ? false, ... } @ args:
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stdenv.mkDerivation (args // {
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<replaceable>...</replaceable> if doCoverageAnalysis then "bla" else "" <replaceable>...</replaceable>
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})
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</programlisting>
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instead of
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<programlisting>
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args:
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args.stdenv.mkDerivation (args // {
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<replaceable>...</replaceable> if args ? doCoverageAnalysis && args.doCoverageAnalysis then "bla" else "" <replaceable>...</replaceable>
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})
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</programlisting>
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</para></listitem>
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</itemizedlist>
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</section>
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<section xml:id="sec-package-naming"><title>Package naming</title>
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<para>In Nixpkgs, there are generally three different names associated with a package:
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<itemizedlist>
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<listitem><para>The <varname>name</varname> attribute of the
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derivation (excluding the version part). This is what most users
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see, in particular when using
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<command>nix-env</command>.</para></listitem>
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<listitem><para>The variable name used for the instantiated package
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in <filename>all-packages.nix</filename>, and when passing it as a
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dependency to other functions. This is what Nix expression authors
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see. It can also be used when installing using <command>nix-env
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-iA</command>.</para></listitem>
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<listitem><para>The filename for (the directory containing) the Nix
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expression.</para></listitem>
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</itemizedlist>
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Most of the time, these are the same. For instance, the package
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<literal>e2fsprogs</literal> has a <varname>name</varname> attribute
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<literal>"e2fsprogs-<replaceable>version</replaceable>"</literal>, is
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bound to the variable name <varname>e2fsprogs</varname> in
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<filename>all-packages.nix</filename>, and the Nix expression is in
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<filename>pkgs/os-specific/linux/e2fsprogs/default.nix</filename>.
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</para>
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<para>There are a few naming guidelines:
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<itemizedlist>
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<listitem><para>Generally, try to stick to the upstream package
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name.</para></listitem>
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<listitem><para>Don’t use uppercase letters in the
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<literal>name</literal> attribute — e.g.,
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<literal>"mplayer-1.0rc2"</literal> instead of
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<literal>"MPlayer-1.0rc2"</literal>.</para></listitem>
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<listitem><para>The version part of the <literal>name</literal>
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attribute <emphasis>must</emphasis> start with a digit (following a
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dash) — e.g., <literal>"hello-0.3-pre-r3910"</literal> instead of
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<literal>"hello-svn-r3910"</literal>, as the latter would be seen as
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a package named <literal>hello-svn</literal> by
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<command>nix-env</command>.</para></listitem>
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<listitem><para>If package is fetched from git's commit then
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the version part of the name <emphasis>must</emphasis> be the date of that
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(fetched) commit. The date must be in <literal>"YYYY-MM-DD"</literal> format.
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Also add <literal>"git"</literal> to the name - e.g.,
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<literal>"pkgname-git-2014-09-23"</literal>.</para></listitem>
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<listitem><para>Dashes in the package name should be preserved
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in new variable names, rather than converted to underscores
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(which was convention up to around 2013 and most names
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still have underscores instead of dashes) — e.g.,
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<varname>http-parser</varname> instead of
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<varname>http_parser</varname>.</para></listitem>
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<listitem><para>If there are multiple versions of a package, this
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should be reflected in the variable names in
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<filename>all-packages.nix</filename>,
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e.g. <varname>json-c-0-9</varname> and <varname>json-c-0-11</varname>.
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If there is an obvious “default” version, make an attribute like
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<literal>json-c = json-c-0-9;</literal>.
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See also <xref linkend="sec-versioning" /></para></listitem>
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</itemizedlist>
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</para>
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</section>
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<section xml:id="sec-organisation"><title>File naming and organisation</title>
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<para>Names of files and directories should be in lowercase, with
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dashes between words — not in camel case. For instance, it should be
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<filename>all-packages.nix</filename>, not
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<filename>allPackages.nix</filename> or
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<filename>AllPackages.nix</filename>.</para>
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<section xml:id="sec-hierarchy"><title>Hierarchy</title>
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<para>Each package should be stored in its own directory somewhere in
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the <filename>pkgs/</filename> tree, i.e. in
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<filename>pkgs/<replaceable>category</replaceable>/<replaceable>subcategory</replaceable>/<replaceable>...</replaceable>/<replaceable>pkgname</replaceable></filename>.
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Below are some rules for picking the right category for a package.
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Many packages fall under several categories; what matters is the
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<emphasis>primary</emphasis> purpose of a package. For example, the
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<literal>libxml2</literal> package builds both a library and some
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tools; but it’s a library foremost, so it goes under
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<filename>pkgs/development/libraries</filename>.</para>
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<para>When in doubt, consider refactoring the
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<filename>pkgs/</filename> tree, e.g. creating new categories or
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splitting up an existing category.</para>
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<variablelist>
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<varlistentry>
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<term>If it’s used to support <emphasis>software development</emphasis>:</term>
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<listitem>
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<variablelist>
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<varlistentry>
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<term>If it’s a <emphasis>library</emphasis> used by other packages:</term>
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<listitem>
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<para><filename>development/libraries</filename> (e.g. <filename>libxml2</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s a <emphasis>compiler</emphasis>:</term>
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<listitem>
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<para><filename>development/compilers</filename> (e.g. <filename>gcc</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s an <emphasis>interpreter</emphasis>:</term>
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<listitem>
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<para><filename>development/interpreters</filename> (e.g. <filename>guile</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s a (set of) development <emphasis>tool(s)</emphasis>:</term>
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<listitem>
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<variablelist>
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<varlistentry>
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<term>If it’s a <emphasis>parser generator</emphasis> (including lexers):</term>
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<listitem>
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<para><filename>development/tools/parsing</filename> (e.g. <filename>bison</filename>, <filename>flex</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s a <emphasis>build manager</emphasis>:</term>
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<listitem>
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<para><filename>development/tools/build-managers</filename> (e.g. <filename>gnumake</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Else:</term>
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<listitem>
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<para><filename>development/tools/misc</filename> (e.g. <filename>binutils</filename>)</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Else:</term>
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<listitem>
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<para><filename>development/misc</filename></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s a (set of) <emphasis>tool(s)</emphasis>:</term>
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<listitem>
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<para>(A tool is a relatively small program, especially one intented
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to be used non-interactively.)</para>
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<variablelist>
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<varlistentry>
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<term>If it’s for <emphasis>networking</emphasis>:</term>
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<listitem>
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<para><filename>tools/networking</filename> (e.g. <filename>wget</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s for <emphasis>text processing</emphasis>:</term>
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<listitem>
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<para><filename>tools/text</filename> (e.g. <filename>diffutils</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s a <emphasis>system utility</emphasis>, i.e.,
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something related or essential to the operation of a
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system:</term>
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<listitem>
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<para><filename>tools/system</filename> (e.g. <filename>cron</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s an <emphasis>archiver</emphasis> (which may
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include a compression function):</term>
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<listitem>
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<para><filename>tools/archivers</filename> (e.g. <filename>zip</filename>, <filename>tar</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s a <emphasis>compression</emphasis> program:</term>
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<listitem>
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<para><filename>tools/compression</filename> (e.g. <filename>gzip</filename>, <filename>bzip2</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s a <emphasis>security</emphasis>-related program:</term>
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<listitem>
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<para><filename>tools/security</filename> (e.g. <filename>nmap</filename>, <filename>gnupg</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Else:</term>
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<listitem>
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<para><filename>tools/misc</filename></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s a <emphasis>shell</emphasis>:</term>
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<listitem>
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<para><filename>shells</filename> (e.g. <filename>bash</filename>)</para>
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||
</listitem>
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||
</varlistentry>
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||
<varlistentry>
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||
<term>If it’s a <emphasis>server</emphasis>:</term>
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||
<listitem>
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||
<variablelist>
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||
<varlistentry>
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||
<term>If it’s a web server:</term>
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||
<listitem>
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||
<para><filename>servers/http</filename> (e.g. <filename>apache-httpd</filename>)</para>
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||
</listitem>
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||
</varlistentry>
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||
<varlistentry>
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||
<term>If it’s an implementation of the X Windowing System:</term>
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||
<listitem>
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||
<para><filename>servers/x11</filename> (e.g. <filename>xorg</filename> — this includes the client libraries and programs)</para>
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||
</listitem>
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||
</varlistentry>
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||
<varlistentry>
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||
<term>Else:</term>
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||
<listitem>
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||
<para><filename>servers/misc</filename></para>
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||
</listitem>
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||
</varlistentry>
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||
</variablelist>
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||
</listitem>
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||
</varlistentry>
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||
<varlistentry>
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||
<term>If it’s a <emphasis>desktop environment</emphasis>:</term>
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||
<listitem>
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||
<para><filename>desktops</filename> (e.g. <filename>kde</filename>, <filename>gnome</filename>, <filename>enlightenment</filename>)</para>
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||
</listitem>
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||
</varlistentry>
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||
<varlistentry>
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||
<term>If it’s a <emphasis>window manager</emphasis>:</term>
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||
<listitem>
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||
<para><filename>applications/window-managers</filename> (e.g. <filename>awesome</filename>, <filename>compiz</filename>, <filename>stumpwm</filename>)</para>
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||
</listitem>
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||
</varlistentry>
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||
<varlistentry>
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||
<term>If it’s an <emphasis>application</emphasis>:</term>
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||
<listitem>
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||
<para>A (typically large) program with a distinct user
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||
interface, primarily used interactively.</para>
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||
<variablelist>
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||
<varlistentry>
|
||
<term>If it’s a <emphasis>version management system</emphasis>:</term>
|
||
<listitem>
|
||
<para><filename>applications/version-management</filename> (e.g. <filename>subversion</filename>)</para>
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||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>If it’s for <emphasis>video playback / editing</emphasis>:</term>
|
||
<listitem>
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||
<para><filename>applications/video</filename> (e.g. <filename>vlc</filename>)</para>
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||
</listitem>
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||
</varlistentry>
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||
<varlistentry>
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||
<term>If it’s for <emphasis>graphics viewing / editing</emphasis>:</term>
|
||
<listitem>
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||
<para><filename>applications/graphics</filename> (e.g. <filename>gimp</filename>)</para>
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||
</listitem>
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||
</varlistentry>
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||
<varlistentry>
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||
<term>If it’s for <emphasis>networking</emphasis>:</term>
|
||
<listitem>
|
||
<variablelist>
|
||
<varlistentry>
|
||
<term>If it’s a <emphasis>mailreader</emphasis>:</term>
|
||
<listitem>
|
||
<para><filename>applications/networking/mailreaders</filename> (e.g. <filename>thunderbird</filename>)</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>If it’s a <emphasis>newsreader</emphasis>:</term>
|
||
<listitem>
|
||
<para><filename>applications/networking/newsreaders</filename> (e.g. <filename>pan</filename>)</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>If it’s a <emphasis>web browser</emphasis>:</term>
|
||
<listitem>
|
||
<para><filename>applications/networking/browsers</filename> (e.g. <filename>firefox</filename>)</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>Else:</term>
|
||
<listitem>
|
||
<para><filename>applications/networking/misc</filename></para>
|
||
</listitem>
|
||
</varlistentry>
|
||
</variablelist>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>Else:</term>
|
||
<listitem>
|
||
<para><filename>applications/misc</filename></para>
|
||
</listitem>
|
||
</varlistentry>
|
||
</variablelist>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>If it’s <emphasis>data</emphasis> (i.e., does not have a
|
||
straight-forward executable semantics):</term>
|
||
<listitem>
|
||
<variablelist>
|
||
<varlistentry>
|
||
<term>If it’s a <emphasis>font</emphasis>:</term>
|
||
<listitem>
|
||
<para><filename>data/fonts</filename></para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>If it’s related to <emphasis>SGML/XML processing</emphasis>:</term>
|
||
<listitem>
|
||
<variablelist>
|
||
<varlistentry>
|
||
<term>If it’s an <emphasis>XML DTD</emphasis>:</term>
|
||
<listitem>
|
||
<para><filename>data/sgml+xml/schemas/xml-dtd</filename> (e.g. <filename>docbook</filename>)</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>If it’s an <emphasis>XSLT stylesheet</emphasis>:</term>
|
||
<listitem>
|
||
<para>(Okay, these are executable...)</para>
|
||
<para><filename>data/sgml+xml/stylesheets/xslt</filename> (e.g. <filename>docbook-xsl</filename>)</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
</variablelist>
|
||
</listitem>
|
||
</varlistentry>
|
||
</variablelist>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>If it’s a <emphasis>game</emphasis>:</term>
|
||
<listitem>
|
||
<para><filename>games</filename></para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>Else:</term>
|
||
<listitem>
|
||
<para><filename>misc</filename></para>
|
||
</listitem>
|
||
</varlistentry>
|
||
</variablelist>
|
||
|
||
</section>
|
||
|
||
<section xml:id="sec-versioning"><title>Versioning</title>
|
||
|
||
<para>Because 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.</para>
|
||
|
||
<para>If there is only one version of a package, its Nix expression
|
||
should be named <filename>e2fsprogs/default.nix</filename>. If there
|
||
are multiple versions, this should be reflected in the filename,
|
||
e.g. <filename>e2fsprogs/1.41.8.nix</filename> and
|
||
<filename>e2fsprogs/1.41.9.nix</filename>. 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 <filename>firefox/2.0.nix</filename> and
|
||
<filename>firefox/3.5.nix</filename>, respectively (which, at a given
|
||
point, might contain versions <literal>2.0.0.20</literal> and
|
||
<literal>3.5.4</literal>). If a version requires many auxiliary
|
||
files, you can use a subdirectory for each version,
|
||
e.g. <filename>firefox/2.0/default.nix</filename> and
|
||
<filename>firefox/3.5/default.nix</filename>.</para>
|
||
|
||
<para>All versions of a package <emphasis>must</emphasis> be included
|
||
in <filename>all-packages.nix</filename> to make sure that they
|
||
evaluate correctly.</para>
|
||
|
||
</section>
|
||
|
||
</section>
|
||
<section xml:id="sec-sources"><title>Fetching Sources</title>
|
||
<para>There are multiple ways to fetch a package source in nixpkgs. The
|
||
general guidline is that you should package sources with a high degree of
|
||
availability. Right now there is only one fetcher which has mirroring
|
||
support and that is <literal>fetchurl</literal>. Note that you should also
|
||
prefer protocols which have a corresponding proxy environment variable.
|
||
</para>
|
||
<para>You can find many source fetch helpers in <literal>pkgs/build-support/fetch*</literal>.
|
||
</para>
|
||
<para>In the file <literal>pkgs/top-level/all-packages.nix</literal> you can
|
||
find fetch helpers, these have names on the form
|
||
<literal>fetchFrom*</literal>. The intention of these are to provide
|
||
snapshot fetches but using the same api as some of the version controlled
|
||
fetchers from <literal>pkgs/build-support/</literal>. As an example going
|
||
from bad to good:
|
||
<itemizedlist>
|
||
<listitem>
|
||
<para>Uses <literal>git://</literal> which won't be proxied.
|
||
<programlisting>
|
||
src = fetchgit {
|
||
url = "git://github.com/NixOS/nix.git";
|
||
rev = "1f795f9f44607cc5bec70d1300150bfefcef2aae";
|
||
sha256 = "1cw5fszffl5pkpa6s6wjnkiv6lm5k618s32sp60kvmvpy7a2v9kg";
|
||
}
|
||
</programlisting>
|
||
</para>
|
||
</listitem>
|
||
<listitem>
|
||
<para>This is ok, but an archive fetch will still be faster.
|
||
<programlisting>
|
||
src = fetchgit {
|
||
url = "https://github.com/NixOS/nix.git";
|
||
rev = "1f795f9f44607cc5bec70d1300150bfefcef2aae";
|
||
sha256 = "1cw5fszffl5pkpa6s6wjnkiv6lm5k618s32sp60kvmvpy7a2v9kg";
|
||
}
|
||
</programlisting>
|
||
</para>
|
||
</listitem>
|
||
<listitem>
|
||
<para>Fetches a snapshot archive and you get the rev you want.
|
||
<programlisting>
|
||
src = fetchFromGitHub {
|
||
owner = "NixOS";
|
||
repo = "nix";
|
||
rev = "1f795f9f44607cc5bec70d1300150bfefcef2aae";
|
||
sha256 = "04yri911rj9j19qqqn6m82266fl05pz98inasni0vxr1cf1gdgv9";
|
||
}
|
||
</programlisting>
|
||
</para>
|
||
</listitem>
|
||
</itemizedlist>
|
||
</para>
|
||
</section>
|
||
</chapter>
|