run qmlcachegen on registered QML modules

Fixes KDAB#242

crates/cxx-qt-build/src/lib.rs

@@ -373,7 +373,7 @@ where
     }
 
     /// Register a QML module at build time. The specified rust_files should contain cxx-qt bridge modules with QObject types annotated
-    /// with `#[qml_element]`.
+    /// with `#[qml_element]`. When using Qt 6, this will [run qmlcachegen](https://doc.qt.io/qt-6/qtqml-qtquick-compiler-tech.html) to compile the specified .qml files ahead-of-time.
     ///
     /// ```
     /// # use cxx_qt_build::CxxQtBuilder;
@@ -558,6 +558,9 @@ where
             self.cc_builder.file(qml_type_registration_files.plugin);
             cc_builder_whole_archive.file(qml_type_registration_files.plugin_init);
             cc_builder_whole_archive.file(qml_type_registration_files.qrc);
+            for qmlcachegen_file in qml_type_registration_files.qmlcachegen {
+                cc_builder_whole_archive.file(qmlcachegen_file);
+            }
             self.cc_builder.define("QT_STATICPLUGIN", None);
             cc_builder_whole_archive_files_added = true;
         }

crates/qt-build-utils/src/lib.rs

@@ -171,6 +171,8 @@ pub struct QmlModuleRegistrationFiles {
     pub plugin_init: PathBuf,
     /// File generated by rcc for the QML plugin. Must be linked with `+whole-archive`.
     pub qrc: PathBuf,
+    /// Files generated by qmlcachegen. Must be linked with `+whole-archive`.
+    pub qmlcachegen: Vec<PathBuf>,
 }
 
 /// Helper for build.rs scripts using Qt
@@ -186,6 +188,7 @@ pub struct QtBuild {
     qmake_executable: String,
     moc_executable: Option<String>,
     qmltyperegistrar_executable: Option<String>,
+    qmlcachegen_executable: Option<String>,
     rcc_executable: Option<String>,
     qt_modules: Vec<String>,
 }
@@ -286,6 +289,7 @@ impl QtBuild {
                         qmake_executable: executable_name.to_string(),
                         moc_executable: None,
                         qmltyperegistrar_executable: None,
+                        qmlcachegen_executable: None,
                         rcc_executable: None,
                         version,
                         qt_modules,
@@ -309,6 +313,7 @@ impl QtBuild {
                         qmake_executable: executable_name.to_string(),
                         moc_executable: None,
                         qmltyperegistrar_executable: None,
+                        qmlcachegen_executable: None,
                         rcc_executable: None,
                         version,
                         qt_modules,
@@ -618,6 +623,7 @@ impl QtBuild {
     }
 
     /// Generate C++ files to automatically register a QML module at build time using the JSON output from [moc](Self::moc).
+    /// When using Qt 6, this will [run qmlcachegen](https://doc.qt.io/qt-6/qtqml-qtquick-compiler-tech.html) to compile the specified .qml files ahead-of-time.
     pub fn register_qml_module<A, B>(
         &mut self,
         metatypes_json: &[impl AsRef<Path>],
@@ -634,6 +640,12 @@ impl QtBuild {
                     .expect("Could not find qmltyperegistrar"),
             );
         }
+        // qmlcachegen has a different CLI in Qt 5, so only support Qt >= 6
+        if self.qmlcachegen_executable.is_none() && self.version.major >= 6 {
+            if let Ok(qmlcachegen_executable) = self.get_qt_tool("qmlcachegen") {
+                self.qmlcachegen_executable = Some(qmlcachegen_executable);
+            }
+        }
 
         let uri = &qml_module.uri;
         let qml_uri_dirs = uri.replace('.', "/");
@@ -646,8 +658,8 @@ impl QtBuild {
         let typeinfo_path = format!("{qml_uri_cpp_symbol_safe}.qmltypes");
         let plugin_class_name = format!("{qml_uri_cpp_symbol_safe}_plugin");
 
-        let mut qmldir =
-            File::create(format!("{qml_module_dir}/qmldir")).expect("Could not create qmldir file");
+        let qmldir_file_path = format!("{qml_module_dir}/qmldir");
+        let mut qmldir = File::create(&qmldir_file_path).expect("Could not create qmldir file");
         write!(
             qmldir,
             "module {uri}
@@ -770,11 +782,94 @@ Q_IMPORT_PLUGIN({plugin_class_name});
         )
         .unwrap();
 
+        let mut qmlcachegen_file_paths = Vec::new();
+        // qmlcachegen needs to be run once for each .qml file with --resource-path,
+        // then once for the module with --resource-name.
+        if let Some(qmlcachegen_executable) = &self.qmlcachegen_executable {
+            let qmlcachegen_dir = format!("{out_dir}/qmlcachegen/{qml_uri_dirs}");
+            std::fs::create_dir_all(&qmlcachegen_dir)
+                .expect("Could not create qmlcachegen directory for QML module");
+
+            let common_args = vec![
+                "-i".to_string(),
+                qmldir_file_path.to_string(),
+                "--resource".to_string(),
+                qrc_path.clone(),
+            ];
+
+            let mut qml_file_qrc_paths = Vec::new();
+            for file in qml_module.qml_files {
+                let qrc_resource_path =
+                    format!("/qt/qml/{qml_uri_dirs}/{}", file.as_ref().display());
+
+                let qml_compiled_file = format!(
+                    "{qmlcachegen_dir}/{}.cpp",
+                    file.as_ref().file_name().unwrap().to_string_lossy()
+                );
+                qmlcachegen_file_paths.push(PathBuf::from(&qml_compiled_file));
+
+                let specific_args = vec![
+                    "--resource-path".to_string(),
+                    qrc_resource_path.clone(),
+                    "-o".to_string(),
+                    qml_compiled_file,
+                    std::fs::canonicalize(file)
+                        .unwrap()
+                        .to_string_lossy()
+                        .to_string(),
+                ];
+
+                let cmd = Command::new(qmlcachegen_executable)
+                    .args(common_args.iter().chain(&specific_args))
+                    .output()
+                    .unwrap_or_else(|_| {
+                        panic!(
+                            "qmlcachegen failed for {} in QML module {uri}",
+                            file.as_ref().display()
+                        )
+                    });
+                if !cmd.status.success() {
+                    panic!(
+                        "qmlcachegen failed for {} in QML module {uri}:\n{}",
+                        file.as_ref().display(),
+                        String::from_utf8_lossy(&cmd.stderr)
+                    );
+                }
+                qml_file_qrc_paths.push(qrc_resource_path);
+            }
+
+            let qmlcachegen_loader = format!("{qmlcachegen_dir}/qmlcache_loader.cpp");
+            let specific_args = vec![
+                "--resource-name".to_string(),
+                format!("qmlcache_{qml_uri_cpp_symbol_safe}"),
+                "-o".to_string(),
+                qmlcachegen_loader.clone(),
+            ];
+
+            let cmd = Command::new(qmlcachegen_executable)
+                .args(
+                    common_args
+                        .iter()
+                        .chain(&specific_args)
+                        .chain(&qml_file_qrc_paths),
+                )
+                .output()
+                .unwrap_or_else(|_| panic!("qmlcachegen failed for QML module {uri}"));
+            if !cmd.status.success() {
+                panic!(
+                    "qmlcachegen failed for QML module {uri}:\n{}",
+                    String::from_utf8_lossy(&cmd.stderr)
+                );
+            }
+            qmlcachegen_file_paths.push(PathBuf::from(&qmlcachegen_loader));
+        }
+
         QmlModuleRegistrationFiles {
             qmltyperegistrar: output_path,
             plugin: qml_plugin_cpp_path,
             plugin_init: qml_plugin_init_path,
             qrc: qrc_output,
+            qmlcachegen: qmlcachegen_file_paths,
         }
     }