74 lines
3.4 KiB
XML
74 lines
3.4 KiB
XML
<section xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xml:id="sec-language-qt">
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<title>Qt</title>
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<para>
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Qt is a comprehensive desktop and mobile application development toolkit for
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C++. Legacy support is available for Qt 3 and Qt 4, but all current
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development uses Qt 5. The Qt 5 packages in Nixpkgs are updated frequently to
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take advantage of new features, but older versions are typically retained
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until their support window ends. The most important consideration in
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packaging Qt-based software is ensuring that each package and all its
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dependencies use the same version of Qt 5; this consideration motivates most
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of the tools described below.
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</para>
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<section xml:id="ssec-qt-libraries">
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<title>Packaging Libraries for Nixpkgs</title>
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<para>
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Whenever possible, libraries that use Qt 5 should be built with each
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available version. Packages providing libraries should be added to the
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top-level function <varname>mkLibsForQt5</varname>, which is used to build a
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set of libraries for every Qt 5 version. A special
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<varname>callPackage</varname> function is used in this scope to ensure that
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the entire dependency tree uses the same Qt 5 version. Import dependencies
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unqualified, i.e., <literal>qtbase</literal> not
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<literal>qt5.qtbase</literal>. <emphasis>Do not</emphasis> import a package
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set such as <literal>qt5</literal> or <literal>libsForQt5</literal>.
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</para>
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<para>
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If a library does not support a particular version of Qt 5, it is best to
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mark it as broken by setting its <literal>meta.broken</literal> attribute. A
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package may be marked broken for certain versions by testing the
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<literal>qtbase.version</literal> attribute, which will always give the
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current Qt 5 version.
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</para>
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</section>
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<section xml:id="ssec-qt-applications">
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<title>Packaging Applications for Nixpkgs</title>
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<para>
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Call your application expression using
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<literal>libsForQt5.callPackage</literal> instead of
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<literal>callPackage</literal>. Import dependencies unqualified, i.e.,
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<literal>qtbase</literal> not <literal>qt5.qtbase</literal>. <emphasis>Do
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not</emphasis> import a package set such as <literal>qt5</literal> or
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<literal>libsForQt5</literal>.
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</para>
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<para>
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Qt 5 maintains strict backward compatibility, so it is generally best to
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build an application package against the latest version using the
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<varname>libsForQt5</varname> library set. In case a package does not build
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with the latest Qt version, it is possible to pick a set pinned to a
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particular version, e.g. <varname>libsForQt55</varname> for Qt 5.5, if that
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is the latest version the package supports. If a package must be pinned to
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an older Qt version, be sure to file a bug upstream; because Qt is strictly
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backwards-compatible, any incompatibility is by definition a bug in the
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application.
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</para>
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<para>
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When testing applications in Nixpkgs, it is a common practice to build the
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package with <literal>nix-build</literal> and run it using the created
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symbolic link. This will not work with Qt applications, however, because
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they have many hard runtime requirements that can only be guaranteed if the
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package is actually installed. To test a Qt application, install it with
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<literal>nix-env</literal> or run it inside <literal>nix-shell</literal>.
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</para>
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</section>
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</section>
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