160 lines
4.1 KiB
Markdown
160 lines
4.1 KiB
Markdown
# Qt {#sec-language-qt}
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Writing Nix expressions for Qt libraries and applications is largely similar as for other C++ software.
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This section assumes some knowledge of the latter.
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There are two problems that the Nixpkgs Qt infrastructure addresses,
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which are not shared by other C++ software:
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1. There are usually multiple supported versions of Qt in Nixpkgs.
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All of a package's dependencies must be built with the same version of Qt.
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This is similar to the version constraints imposed on interpreted languages like Python.
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2. Qt makes extensive use of runtime dependency detection.
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Runtime dependencies are made into build dependencies through wrappers.
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## Nix expression for a Qt package (default.nix) {#qt-default-nix}
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```{=docbook}
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<programlisting>
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{ stdenv, lib, qtbase, wrapQtAppsHook }: <co xml:id='qt-default-nix-co-1' />
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stdenv.mkDerivation {
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pname = "myapp";
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version = "1.0";
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buildInputs = [ qtbase ];
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nativeBuildInputs = [ wrapQtAppsHook ]; <co xml:id='qt-default-nix-co-2' />
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}
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</programlisting>
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<calloutlist>
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<callout arearefs='qt-default-nix-co-1'>
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<para>
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Import Qt modules directly, that is: <literal>qtbase</literal>, <literal>qtdeclarative</literal>, etc.
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<emphasis>Do not</emphasis> import Qt package sets such as <literal>qt5</literal>
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because the Qt versions of dependencies may not be coherent, causing build and runtime failures.
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</para>
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</callout>
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<callout arearefs='qt-default-nix-co-2'>
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<para>
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All Qt packages must include <literal>wrapQtAppsHook</literal> in
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<literal>nativeBuildInputs</literal>, or you must explicitly set
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<literal>dontWrapQtApps</literal>.
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</para>
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</callout>
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</calloutlist>
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```
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## Locating runtime dependencies {#qt-runtime-dependencies}
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Qt applications must be wrapped to find runtime dependencies.
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Include `wrapQtAppsHook` in `nativeBuildInputs`:
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```nix
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{ stdenv, wrapQtAppsHook }:
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stdenv.mkDerivation {
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# ...
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nativeBuildInputs = [ wrapQtAppsHook ];
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}
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```
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Add entries to `qtWrapperArgs` are to modify the wrappers created by
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`wrapQtAppsHook`:
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```nix
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{ stdenv, wrapQtAppsHook }:
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stdenv.mkDerivation {
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# ...
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nativeBuildInputs = [ wrapQtAppsHook ];
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qtWrapperArgs = [ ''--prefix PATH : /path/to/bin'' ];
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}
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```
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The entries are passed as arguments to [wrapProgram](#fun-wrapProgram).
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Set `dontWrapQtApps` to stop applications from being wrapped automatically.
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Wrap programs manually with `wrapQtApp`, using the syntax of
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[wrapProgram](#fun-wrapProgram):
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```nix
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{ stdenv, lib, wrapQtAppsHook }:
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stdenv.mkDerivation {
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# ...
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nativeBuildInputs = [ wrapQtAppsHook ];
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dontWrapQtApps = true;
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preFixup = ''
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wrapQtApp "$out/bin/myapp" --prefix PATH : /path/to/bin
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'';
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}
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```
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::: {.note}
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`wrapQtAppsHook` ignores files that are non-ELF executables.
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This means that scripts won't be automatically wrapped so you'll need to manually wrap them as previously mentioned.
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An example of when you'd always need to do this is with Python applications that use PyQt.
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:::
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## Adding a library to Nixpkgs {#adding-a-library-to-nixpkgs}
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Add Qt libraries to `qt5-packages.nix` to make them available for every
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supported Qt version.
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### Example adding a Qt library {#qt-library-all-packages-nix}
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The following represents the contents of `qt5-packages.nix`.
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```nix
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{
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# ...
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mylib = callPackage ../path/to/mylib {};
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# ...
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}
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```
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Libraries are built with every available version of Qt.
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Use the `meta.broken` attribute to disable the package for unsupported Qt versions:
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```nix
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{ stdenv, lib, qtbase }:
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stdenv.mkDerivation {
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# ...
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# Disable this library with Qt < 5.9.0
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meta.broken = lib.versionOlder qtbase.version "5.9.0";
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}
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```
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## Adding an application to Nixpkgs {#adding-an-application-to-nixpkgs}
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Add Qt applications to `qt5-packages.nix`. Add an alias to `all-packages.nix`
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to select the Qt 5 version used for the application.
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### Example adding a Qt application {#qt-application-all-packages-nix}
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The following represents the contents of `qt5-packages.nix`.
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```nix
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{
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# ...
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myapp = callPackage ../path/to/myapp {};
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# ...
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}
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```
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The following represents the contents of `all-packages.nix`.
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```nix
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{
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# ...
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myapp = libsForQt5.myapp;
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# ...
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}
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```
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