core/scriptmodel: add expression model for unique lists

src/core/scriptmodel.hpp

@@ -0,0 +1,74 @@
+#pragma once
+
+#include <qabstractitemmodel.h>
+#include <qcontainerfwd.h>
+#include <qproperty.h>
+#include <qqmlintegration.h>
+#include <qtmetamacros.h>
+
+///! QML model reflecting a javascript expression
+/// ScriptModel is a QML [Data Model] that generates model operations based on changes
+/// to a javascript expression attached to @@values.
+///
+/// ### When should I use this
+/// ScriptModel should be used when you would otherwise use a javascript expression as a model,
+/// [QAbstractItemModel] is accepted, and the data is likely to change over the lifetime of the program.
+///
+/// When directly using a javascript expression as a model, types like @@QtQuick.Repeater or @@QtQuick.ListView
+/// will destroy all created delegates, and re-create the entire list. In the case of @@QtQuick.ListView this
+/// will also prevent animations from working. If you wrap your expression with ScriptModel, only new items
+/// will be created, and ListView animations will work as expected.
+///
+/// ### Example
+/// ```qml
+/// // Will cause all delegates to be re-created every time filterText changes.
+/// @@QtQuick.Repeater {
+///   model: myList.filter(entry => entry.name.startsWith(filterText))
+///   delegate: // ...
+/// }
+///
+/// // Will add and remove delegates only when required.
+/// @@QtQuick.Repeater {
+///   model: ScriptModel {
+///     values: myList.filter(entry => entry.name.startsWith(filterText))
+///   }
+///
+///   delegate: // ...
+/// }
+/// ```
+class ScriptModel: public QAbstractListModel {
+	Q_OBJECT;
+	/// The list of values to reflect in the model.
+	/// > [!WARNING] ScriptModel currently only works with lists of *unique* values.
+	/// > There must not be any duplicates in the given list, or behavior of the model is undefined.
+	///
+	/// > [!TIP] @@ObjectModel$s supplied by Quickshell types will only contain unique values,
+	/// > and can be used like so:
+	/// >
+	/// > ```qml
+	/// > ScriptModel {
+	/// >   values: DesktopEntries.applications.values.filter(...)
+	/// > }
+	/// > ```
+	/// >
+	/// > Note that we are using @@DesktopEntries.values because it will cause @@ScriptModel.values
+	/// > to receive an update on change.
+	Q_PROPERTY(QVariantList values READ values WRITE setValues NOTIFY valuesChanged);
+	QML_ELEMENT;
+
+public:
+	[[nodiscard]] const QVariantList& values() const { return this->mValues; }
+	void setValues(const QVariantList& newValues);
+
+	[[nodiscard]] qint32 rowCount(const QModelIndex& parent) const override;
+	[[nodiscard]] QVariant data(const QModelIndex& index, qint32 role) const override;
+	[[nodiscard]] QHash<int, QByteArray> roleNames() const override;
+
+signals:
+	void valuesChanged();
+
+private:
+	QVariantList mValues;
+
+	void updateValuesUnique(const QVariantList& newValues);
+};