<section xmlns="http://docbook.org/ns/docbook"
         xmlns:xlink="http://www.w3.org/1999/xlink"
         xml:id="sec-xorg">
 <title>X.org</title>

 <para>
  The Nix expressions for the X.org packages reside in <filename>pkgs/servers/x11/xorg/default.nix</filename>. This file is automatically generated from lists of tarballs in an X.org release. As such it should not be modified directly; rather, you should modify the lists, the generator script or the file <filename>pkgs/servers/x11/xorg/overrides.nix</filename>, in which you can override or add to the derivations produced by the generator.
 </para>

 <para>
  The generator is invoked as follows:
<screen>
<prompt>$ </prompt>cd pkgs/servers/x11/xorg
<prompt>$ </prompt>cat tarballs-7.5.list extra.list old.list \
  | perl ./generate-expr-from-tarballs.pl
</screen>
  For each of the tarballs in the <filename>.list</filename> files, the script downloads it, unpacks it, and searches its <filename>configure.ac</filename> and <filename>*.pc.in</filename> files for dependencies. This information is used to generate <filename>default.nix</filename>. The generator caches downloaded tarballs between runs. Pay close attention to the <literal>NOT FOUND: <replaceable>name</replaceable></literal> messages at the end of the run, since they may indicate missing dependencies. (Some might be optional dependencies, however.)
 </para>

 <para>
  A file like <filename>tarballs-7.5.list</filename> contains all tarballs in a X.org release. It can be generated like this:
<screen>
<prompt>$ </prompt>export i="mirror://xorg/X11R7.4/src/everything/"
<prompt>$ </prompt>cat $(PRINT_PATH=1 nix-prefetch-url $i | tail -n 1) \
  | perl -e 'while (&lt;>) { if (/(href|HREF)="([^"]*.bz2)"/) { print "$ENV{'i'}$2\n"; }; }' \
  | sort > tarballs-7.4.list
</screen>
  <filename>extra.list</filename> contains libraries that aren’t part of X.org proper, but are closely related to it, such as <literal>libxcb</literal>. <filename>old.list</filename> contains some packages that were removed from X.org, but are still needed by some people or by other packages (such as <varname>imake</varname>).
 </para>

 <para>
  If the expression for a package requires derivation attributes that the generator cannot figure out automatically (say, <varname>patches</varname> or a <varname>postInstall</varname> hook), you should modify <filename>pkgs/servers/x11/xorg/overrides.nix</filename>.
 </para>
</section>
