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<section xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink"
xml:id="sec-language-qt">
<title>Qt</title>
<para>
This section describes the differences between Nix expressions for Qt
libraries and applications and Nix expressions for other C++ software. Some
knowledge of the latter is assumed. There are primarily two problems which
the Qt infrastructure is designed to address: ensuring consistent versioning
of all dependencies and finding dependencies at runtime.
</para>
<example xml:id='qt-default-nix'>
<title>Nix expression for a Qt package (<filename>default.nix</filename>)</title>
<programlisting>
{ mkDerivation, lib, qtbase }: <co xml:id='qt-default-nix-co-1' />
mkDerivation { <co xml:id='qt-default-nix-co-2' />
pname = "myapp";
version = "1.0";
buildInputs = [ qtbase ]; <co xml:id='qt-default-nix-co-3' />
}
</programlisting>
</example>
<calloutlist>
<callout arearefs='qt-default-nix-co-1'>
<para>
Import <literal>mkDerivation</literal> and Qt (such as
<literal>qtbase</literal> modules directly. <emphasis>Do not</emphasis>
import Qt package sets; the Qt versions of dependencies may not be
coherent, causing build and runtime failures.
</para>
</callout>
<callout arearefs='qt-default-nix-co-2'>
<para>
Use <literal>mkDerivation</literal> instead of
<literal>stdenv.mkDerivation</literal>. <literal>mkDerivation</literal>
is a wrapper around <literal>stdenv.mkDerivation</literal> which
applies some Qt-specific settings.
This deriver accepts the same arguments as
<literal>stdenv.mkDerivation</literal>; refer to
<xref linkend='chap-stdenv' /> for details.
</para>
<para>
To use another deriver instead of
<literal>stdenv.mkDerivation</literal>, use
<literal>mkDerivationWith</literal>:
<programlisting>
mkDerivationWith myDeriver {
# ...
}
</programlisting>
If you cannot use <literal>mkDerivationWith</literal>, please refer to
<xref linkend='qt-runtime-dependencies' />.
</para>
</callout>
<callout arearefs='qt-default-nix-co-3'>
<para>
<literal>mkDerivation</literal> accepts the same arguments as
<literal>stdenv.mkDerivation</literal>, such as
<literal>buildInputs</literal>.
</para>
</callout>
</calloutlist>
<formalpara xml:id='qt-runtime-dependencies'>
<title>Locating runtime dependencies</title>
<para>
Qt applications need to be wrapped to find runtime dependencies. If you
cannot use <literal>mkDerivation</literal> or
<literal>mkDerivationWith</literal> above, include
<literal>wrapQtAppsHook</literal> in <literal>nativeBuildInputs</literal>:
<programlisting>
stdenv.mkDerivation {
# ...
nativeBuildInputs = [ wrapQtAppsHook ];
}
</programlisting>
</para>
</formalpara>
<para>
Entries added to <literal>qtWrapperArgs</literal> are used to modify the
wrappers created by <literal>wrapQtAppsHook</literal>. The entries are
passed as arguments to <xref linkend='fun-wrapProgram' />.
<programlisting>
mkDerivation {
# ...
qtWrapperArgs = [ ''--prefix PATH : /path/to/bin'' ];
}
</programlisting>
</para>
<para>
Set <literal>dontWrapQtApps</literal> to stop applications from being
wrapped automatically. It is required to wrap applications manually with
<literal>wrapQtApp</literal>, using the syntax of
<xref linkend='fun-wrapProgram' />:
<programlisting>
mkDerivation {
# ...
dontWrapQtApps = true;
preFixup = ''
wrapQtApp "$out/bin/myapp" --prefix PATH : /path/to/bin
'';
}
</programlisting>
</para>
<para>
Libraries are built with every available version of Qt. Use the <literal>meta.broken</literal>
attribute to disable the package for unsupported Qt versions:
<programlisting>
mkDerivation {
# ...
# Disable this library with Qt < 5.9.0
meta.broken = builtins.compareVersions qtbase.version "5.9.0" < 0;
}
</programlisting>
</para>
<formalpara>
<title>Adding a library to Nixpkgs</title>
<para>
Add a Qt library to <filename>all-packages.nix</filename> by adding it to the
collection inside <literal>mkLibsForQt5</literal>. This ensures that the
library is built with every available version of Qt as needed.
<example xml:id='qt-library-all-packages-nix'>
<title>Adding a Qt library to <filename>all-packages.nix</filename></title>
<programlisting>
{
# ...
mkLibsForQt5 = self: with self; {
# ...
mylib = callPackage ../path/to/mylib {};
};
# ...
}
</programlisting>
</example>
</para>
</formalpara>
<formalpara>
<title>Adding an application to Nixpkgs</title>
<para>
Add a Qt application to <filename>all-packages.nix</filename> using
<literal>libsForQt5.callPackage</literal> instead of the usual
<literal>callPackage</literal>. The former ensures that all dependencies
are built with the same version of Qt.
<example xml:id='qt-application-all-packages-nix'>
<title>Adding a Qt application to <filename>all-packages.nix</filename></title>
<programlisting>
{
# ...
myapp = libsForQt5.callPackage ../path/to/myapp/ {};
# ...
}
</programlisting>
</example>
</para>
</formalpara>
</section>
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