79 lines
2.4 KiB
Markdown
79 lines
2.4 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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The major caveat with Qt applications is that Qt uses a plugin system to load additional modules at runtime,
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from a list of well-known locations. In Nixpkgs, we patch QtCore to instead use an environment variable,
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and wrap Qt applications to set it to the right paths. This effectively makes the runtime dependencies
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pure and explicit at build-time, at the cost of introducing 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, lib, qtbase, wrapQtAppsHook }:
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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 ];
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}
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```
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It is important to import Qt modules directly, that is: `qtbase`, `qtdeclarative`, etc. *Do not* import Qt package sets such as `qt5` because the Qt versions of dependencies may not be coherent, causing build and runtime failures.
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Additionally all Qt packages must include `wrapQtAppsHook` in `nativeBuildInputs`, or you must explicitly set `dontWrapQtApps`.
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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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