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Add support for C++ QML Elements in CxxQtBuilder #1146

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4d12f16
Add support for C++ QML QObjects in CxxQtBuilder
Dec 19, 2024
070fc5f
fix moc call
Aug 8, 2025
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34 changes: 34 additions & 0 deletions crates/cxx-qt-build/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -377,6 +377,7 @@ pub struct CxxQtBuilder {
include_prefix: String,
crate_include_root: Option<String>,
additional_include_dirs: Vec<PathBuf>,
qml_qobjects: Vec<(PathBuf, PathBuf)>,
}

impl CxxQtBuilder {
Expand Down Expand Up @@ -418,6 +419,7 @@ impl CxxQtBuilder {
include_prefix: crate_name(),
crate_include_root: Some(String::new()),
additional_include_dirs: vec![],
qml_qobjects: vec![],
}
}

Expand Down Expand Up @@ -588,6 +590,22 @@ impl CxxQtBuilder {
self
}

/// Specify a C++ header and source file containing a Q_OBJECT macro to run [moc](https://doc.qt.io/qt-6/moc.html) on.
/// Unlike [CxxQtBuilder::qobject_header], it includes the generated metatypes.json, so that C++ classes can be included
/// in QML modules.
Comment on lines +594 to +595
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Copilot AI Aug 8, 2025

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The documentation should clarify the difference between this method and qobject_header more explicitly. Currently it only mentions that it 'includes the generated metatypes.json' but doesn't explain when to use each method.

Suggested change
/// Unlike [CxxQtBuilder::qobject_header], it includes the generated metatypes.json, so that C++ classes can be included
/// in QML modules.
///
/// This method is intended for integrating C++ QObject subclasses into QML modules. In addition to running `moc` on the provided files,
/// it generates and includes the `metatypes.json` file required for QML registration, allowing the C++ classes to be used directly in QML.
///
/// In contrast, [`CxxQtBuilder::qobject_header`] only runs `moc` on a header file and does **not** generate or include `metatypes.json`.
/// Use `qobject_header` when you only need to integrate a C++ QObject subclass with Qt (for example, for signal/slot support in C++),
/// but do **not** need to expose the class to QML.
///
/// **Use this method (`qml_qobject`) when you want your C++ QObject to be available in QML.**

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pub fn qml_qobject(
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cpp_qobject ? I guess this could have other applications outside of QML

mut self,
qobject_header: impl AsRef<Path>,
qobject_source: impl AsRef<Path>,
) -> Self {
let qobject_header = qobject_header.as_ref().to_path_buf();
let qobject_source = qobject_source.as_ref().to_path_buf();
println!("cargo::rerun-if-changed={}", qobject_header.display());
println!("cargo::rerun-if-changed={}", qobject_source.display());
self.qml_qobjects.push((qobject_header, qobject_source));
self
}

/// Use a closure to run additional customization on [CxxQtBuilder]'s internal [cc::Build]
/// before calling [CxxQtBuilder::build]. This allows to add extra include paths, compiler flags,
/// or anything else available via [cc::Build]'s API. For example, to add an include path for
Expand Down Expand Up @@ -869,6 +887,22 @@ impl CxxQtBuilder {
}
}

for (qobject_header, qobject_source) in &self.qml_qobjects {
cc_builder.file(qobject_source);
if let Some(dir) = qobject_header.parent() {
moc_include_paths.insert(dir.to_path_buf());
}
let moc_products = qtbuild.moc().compile(
qobject_header,
MocArguments::default().uri(qml_module.uri.clone()),
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The qml_module.uri is being cloned inside a loop. Consider cloning it once before the loop and reusing the cloned value to avoid repeated allocations.

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MocArguments::default().uri(qml_module.uri.clone()),
MocArguments::default().uri(qml_module_uri.clone()),

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);
if let Some(dir) = moc_products.cpp.parent() {
moc_include_paths.insert(dir.to_path_buf());
}
cc_builder.file(moc_products.cpp);
qml_metatypes_json.push(moc_products.metatypes_json);
}

let qml_module_registration_files = qtbuild.register_qml_module(
&qml_metatypes_json,
&qml_module.uri,
Expand Down
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