82 lines
3 KiB
Markdown
82 lines
3 KiB
Markdown
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# 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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The major caveat with Qt applications is that Qt uses a plugin system to load additional modules at runtime.
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In Nixpkgs, we wrap Qt applications to inject environment variables telling Qt where to discover the required plugins and QML modules.
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This effectively makes the runtime dependencies pure and explicit at build-time, at the cost of introducing
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an extra indirection.
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## Nix expression for a Qt package (default.nix) {#qt-default-nix}
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```nix
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{ stdenv, qt6 }:
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stdenv.mkDerivation {
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pname = "myapp";
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version = "1.0";
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buildInputs = [ qt6.qtbase ];
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nativeBuildInputs = [ qt6.wrapQtAppsHook ];
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}
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```
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The same goes for Qt 5 where libraries and tools are under `libsForQt5`.
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Any Qt package should include `wrapQtAppsHook` in `nativeBuildInputs`, or explicitly set `dontWrapQtApps` to bypass generating the wrappers.
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::: {.note}
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Qt 6 graphical applications should also include `qtwayland` in `buildInputs` on Linux (but not on platforms e.g. Darwin, where `qtwayland` is not available), to ensure the Wayland platform plugin is available.
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This may become default in the future, see [NixOS/nixpkgs#269674](https://github.com/NixOS/nixpkgs/pull/269674).
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:::
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## Packages supporting multiple Qt versions {#qt-versions}
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If your package is a library that can be built with multiple Qt versions, you may want to take Qt modules as separate arguments (`qtbase`, `qtdeclarative` etc.), and invoke the package from `pkgs/top-level/qt5-packages.nix` or `pkgs/top-level/qt6-packages.nix` using the respective `callPackage` functions.
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Applications should generally be built with upstream's preferred Qt version.
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## Locating additional runtime dependencies {#qt-runtime-dependencies}
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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, qt6 }:
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stdenv.mkDerivation {
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# ...
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nativeBuildInputs = [ qt6.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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If you need more control over the wrapping process, set `dontWrapQtApps` to disable automatic wrapper generation,
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and then create wrappers manually in `fixupPhase`, using `wrapQtApp`, which itself is a small wrapper over [wrapProgram](#fun-wrapProgram):
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The `makeWrapper` arguments required for Qt are also exposed in the environment as `$qtWrapperArgs`.
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```nix
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{ stdenv, lib, wrapQtAppsHook }:
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stdenv.mkDerivation {
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# ...
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nativeBuildInputs = [ wrapQtAppsHook ];
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dontWrapQtApps = true;
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preFixup = ''
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wrapQtApp "$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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