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