Initial import of the Qt C++ property binding system

This implements the core value based property binding system with
automatic dependency tracking. More features are to be added later, and
the documentation will need further improvements as well.

Change-Id: I77ec9163ba4dace6c4451f5933962ebe1b3b4b14
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 671 insertions, 0 deletions

diff --git a/src/corelib/kernel/qproperty.cpp b/src/corelib/kernel/qproperty.cpp
new file mode 100644
index 0000000000..75110fa031
--- /dev/null
+++ b/src/corelib/kernel/qproperty.cpp
@@ -0,0 +1,671 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qproperty.h"
+#include "qproperty_p.h"
+#include "qpropertybinding_p.h"
+
+#include <qscopedvaluerollback.h>
+
+QT_BEGIN_NAMESPACE
+
+using namespace QtPrivate;
+
+QPropertyBase::QPropertyBase(QPropertyBase &&other, void *propertyDataPtr)
+{
+    std::swap(d_ptr, other.d_ptr);
+    QPropertyBasePointer d{this};
+    d.firstObserverPtr().set(nullptr);
+    if (auto binding = d.bindingPtr())
+        binding->propertyDataPtr = propertyDataPtr;
+}
+
+void QPropertyBase::moveAssign(QPropertyBase &&other, void *propertyDataPtr)
+{
+    if (&other == this)
+        return;
+
+    QPropertyBasePointer d{this};
+    auto observer = d.firstObserver();
+    d.firstObserverPtr().set(nullptr);
+
+    if (auto binding = d.bindingPtr()) {
+        binding->unlinkAndDeref();
+        d_ptr &= FlagMask;
+    }
+
+    std::swap(d_ptr, other.d_ptr);
+
+    if (auto binding = d.bindingPtr())
+        binding->propertyDataPtr = propertyDataPtr;
+
+    d.firstObserverPtr().set(const_cast<QPropertyObserver*>(observer.ptr));
+
+    // The caller will have to notify observers.
+}
+
+QPropertyBase::~QPropertyBase()
+{
+    QPropertyBasePointer d{this};
+    if (auto observer = d.firstObserver())
+        observer.unlink();
+    if (auto binding = d.bindingPtr())
+        binding->unlinkAndDeref();
+}
+
+QUntypedPropertyBinding QPropertyBase::setBinding(const QUntypedPropertyBinding &binding, void *propertyDataPtr)
+{
+    QPropertyBindingPrivatePtr oldBinding;
+    QPropertyBindingPrivatePtr newBinding = binding.d;
+
+    QPropertyBasePointer d{this};
+
+    auto observer = d.firstObserver();
+    if (observer)
+        observer.unlink();
+
+    if (auto *existingBinding = d.bindingPtr()) {
+        if (existingBinding == newBinding.data())
+            return QUntypedPropertyBinding(oldBinding);
+        oldBinding = QPropertyBindingPrivatePtr(existingBinding);
+        oldBinding->unlinkAndDeref();
+        d_ptr &= FlagMask;
+    }
+    if (newBinding) {
+        newBinding.data()->ref.ref();
+        d_ptr = (d_ptr & FlagMask) | reinterpret_cast<quintptr>(newBinding.data());
+        d_ptr |= BindingBit;
+        newBinding->dirty = true;
+        newBinding->propertyDataPtr = propertyDataPtr;
+        if (observer)
+            observer.prependToBinding(newBinding.data());
+    } else {
+        d_ptr &= ~BindingBit;
+    }
+
+    return QUntypedPropertyBinding(oldBinding);
+}
+
+QPropertyBindingPrivatePtr QPropertyBase::binding()
+{
+    QPropertyBasePointer d{this};
+    if (auto binding = d.bindingPtr())
+        return QPropertyBindingPrivatePtr(binding);
+    return QPropertyBindingPrivatePtr();
+}
+
+QPropertyBindingPrivate *QPropertyBasePointer::bindingPtr() const
+{
+    if (ptr->d_ptr & QPropertyBase::BindingBit)
+        return reinterpret_cast<QPropertyBindingPrivate*>(ptr->d_ptr & ~QPropertyBase::FlagMask);
+    return nullptr;
+}
+
+QtPrivate::QPropertyTagPreservingPointerToPointer<QPropertyObserver> QPropertyBasePointer::firstObserverPtr() const
+{
+    if (auto *binding = bindingPtr())
+        return const_cast<QPropertyObserver**>(&binding->firstObserver.ptr);
+    return &ptr->d_ptr;
+}
+
+QPropertyObserverPointer QPropertyBasePointer::firstObserver() const
+{
+    if (auto *binding = bindingPtr())
+        return binding->firstObserver;
+    return {reinterpret_cast<QPropertyObserver*>(ptr->d_ptr & ~QPropertyBase::FlagMask)};
+}
+
+static thread_local BindingEvaluationState *currentBindingEvaluationState = nullptr;
+
+BindingEvaluationState::BindingEvaluationState(QPropertyBindingPrivate *binding)
+    : binding(binding)
+    , dependencyObservers(&binding->dependencyObservers)
+{
+    previousState = currentBindingEvaluationState;
+    currentBindingEvaluationState = this;
+    dependencyObservers->clear();
+}
+
+BindingEvaluationState::~BindingEvaluationState()
+{
+    currentBindingEvaluationState = previousState;
+}
+
+void QPropertyBase::evaluateIfDirty()
+{
+    QPropertyBasePointer d{this};
+    QPropertyBindingPrivate *binding = d.bindingPtr();
+    if (!binding)
+        return;
+    binding->evaluateIfDirtyAndReturnTrueIfValueChanged();
+}
+
+void QPropertyBase::removeBinding()
+{
+    QPropertyBasePointer d{this};
+
+    auto observer = d.firstObserver();
+    if (observer)
+        observer.unlink();
+
+    if (auto *existingBinding = d.bindingPtr()) {
+        existingBinding->unlinkAndDeref();
+        d_ptr &= FlagMask;
+    }
+    d_ptr &= ~BindingBit;
+
+    if (observer)
+        observer.observeProperty(d);
+}
+
+void QPropertyBase::registerWithCurrentlyEvaluatingBinding() const
+{
+    auto currentState = currentBindingEvaluationState;
+    if (!currentState)
+        return;
+
+    QPropertyBasePointer d{this};
+
+    currentState->dependencyObservers->append(QPropertyObserver());
+    QPropertyObserverPointer dependencyObserver{&(*currentState->dependencyObservers)[currentState->dependencyObservers->size() - 1]};
+    dependencyObserver.setBindingToMarkDirty(currentState->binding);
+    dependencyObserver.observeProperty(d);
+}
+
+void QPropertyBase::notifyObservers()
+{
+    QPropertyBasePointer d{this};
+    if (QPropertyObserverPointer observer = d.firstObserver())
+        observer.notify(d.bindingPtr());
+}
+
+int QPropertyBasePointer::observerCount() const
+{
+    int count = 0;
+    for (auto observer = firstObserver(); observer; observer = observer.nextObserver())
+        ++count;
+    return count;
+}
+
+QPropertyObserver::QPropertyObserver(void (*callback)(QPropertyObserver*))
+{
+    QPropertyObserverPointer d{this};
+    d.setChangeHandler(callback);
+}
+
+void QPropertyObserver::setSource(QPropertyBase &property)
+{
+    QPropertyObserverPointer d{this};
+    QPropertyBasePointer propPrivate{&property};
+    d.observeProperty(propPrivate);
+}
+
+
+QPropertyObserver::~QPropertyObserver()
+{
+    QPropertyObserverPointer d{this};
+    d.unlink();
+}
+
+QPropertyObserver::QPropertyObserver(QPropertyObserver &&other)
+{
+    std::swap(bindingToMarkDirty, other.bindingToMarkDirty);
+    std::swap(next, other.next);
+    std::swap(prev, other.prev);
+    if (next)
+        next->prev = reinterpret_cast<quintptr*>(&next);
+    if (prev)
+        prev.set(this);
+}
+
+QPropertyObserver &QPropertyObserver::operator=(QPropertyObserver &&other)
+{
+    if (this == &other)
+        return *this;
+
+    QPropertyObserverPointer d{this};
+    d.unlink();
+    bindingToMarkDirty = nullptr;
+
+    std::swap(bindingToMarkDirty, other.bindingToMarkDirty);
+    std::swap(next, other.next);
+    std::swap(prev, other.prev);
+    if (next)
+        next->prev = reinterpret_cast<quintptr*>(&next);
+    if (prev)
+        prev.set(this);
+
+    return *this;
+}
+
+void QPropertyObserverPointer::unlink()
+{
+    if (ptr->next)
+        ptr->next->prev = ptr->prev;
+    if (ptr->prev)
+        ptr->prev.set(ptr->next.data());
+    ptr->next = nullptr;
+    ptr->prev.clear();
+}
+
+void QPropertyObserverPointer::setChangeHandler(void (*changeHandler)(QPropertyObserver *))
+{
+    ptr->changeHandler = changeHandler;
+    ptr->next.setFlag(true);
+}
+
+void QPropertyObserverPointer::setBindingToMarkDirty(QPropertyBindingPrivate *binding)
+{
+    ptr->bindingToMarkDirty = binding;
+    ptr->next.setFlag(false);
+}
+
+void QPropertyObserverPointer::notify(QPropertyBindingPrivate *triggeringBinding)
+{
+    bool knownIfPropertyChanged = false;
+    bool propertyChanged =true;
+
+    auto observer = const_cast<QPropertyObserver*>(ptr);
+    while (observer) {
+        auto * const next = observer->next.data();
+        if (observer->next.flag()) {
+            if (!knownIfPropertyChanged && triggeringBinding) {
+                knownIfPropertyChanged = true;
+
+                propertyChanged = triggeringBinding->evaluateIfDirtyAndReturnTrueIfValueChanged();
+            }
+            if (!propertyChanged)
+                return;
+
+            if (auto handlerToCall = std::exchange(observer->changeHandler, nullptr)) {
+                handlerToCall(observer);
+                observer->changeHandler = handlerToCall;
+            }
+        } else {
+            if (observer->bindingToMarkDirty)
+                observer->bindingToMarkDirty->markDirtyAndNotifyObservers();
+        }
+        observer = next;
+    }
+}
+
+void QPropertyObserverPointer::observeProperty(QPropertyBasePointer property)
+{
+    unlink();
+    auto firstObserverPtr = property.firstObserverPtr();
+    ptr->prev = firstObserverPtr;
+    ptr->next = firstObserverPtr.get();
+    if (ptr->next)
+        ptr->next->prev = &ptr->next;
+    firstObserverPtr.set(ptr);
+}
+
+void QPropertyObserverPointer::prependToBinding(QPropertyBindingPrivate *binding)
+{
+    ptr->prev = const_cast<QPropertyObserver **>(&binding->firstObserver.ptr);
+    binding->firstObserver = *this;
+}
+
+QPropertyBindingError::QPropertyBindingError(Type type)
+{
+    if (type != NoError) {
+        d = new QPropertyBindingErrorPrivate;
+        d->type = type;
+    }
+}
+
+QPropertyBindingError::QPropertyBindingError(const QPropertyBindingError &other)
+    : d(other.d)
+{
+}
+
+QPropertyBindingError &QPropertyBindingError::operator=(const QPropertyBindingError &other)
+{
+    d = other.d;
+    return *this;
+}
+
+QPropertyBindingError::QPropertyBindingError(QPropertyBindingError &&other)
+    : d(std::move(other.d))
+{
+}
+
+QPropertyBindingError &QPropertyBindingError::operator=(QPropertyBindingError &&other)
+{
+    d = std::move(other.d);
+    return *this;
+}
+
+QPropertyBindingError::~QPropertyBindingError()
+{
+}
+
+QPropertyBindingError::Type QPropertyBindingError::type() const
+{
+    if (!d)
+        return QPropertyBindingError::NoError;
+    return d->type;
+}
+
+void QPropertyBindingError::setDescription(const QString &description)
+{
+    if (!d)
+        d = new QPropertyBindingErrorPrivate;
+    d->description = description;
+}
+
+QString QPropertyBindingError::description() const
+{
+    if (!d)
+        return QString();
+    return d->description;
+}
+
+QPropertyBindingSourceLocation QPropertyBindingError::location() const
+{
+    if (!d)
+        return QPropertyBindingSourceLocation();
+    return d->location;
+}
+
+/*!
+  \class QProperty
+  \inmodule QtCore
+  \brief The QProperty class is a template class that enables automatic property bindings.
+
+  \ingroup tools
+
+  QProperty\<T\> is a generic container that holds an instance of T. You can assign
+  a value to it and you can read it via the value() function or the T conversion
+  operator. You can also tie the property to an expression that computes the value
+  dynamically, the binding expression. It is represented as a C++ lambda and
+  can be used to express relationships between different properties in your
+  application.
+
+  The binding expression computes the value by reading other QProperty values.
+  Behind the scenes this dependency is tracked. Whenever a change in any property's
+  dependency is detected, the binding expression is re-evaluated and the new
+  result is applied to the property. This happens lazily, by marking the binding
+  as dirty and evaluating it only when the property's value is requested. For example:
+
+  \code
+    QProperty<QString> firstname("John");
+    QProperty<QString> lastname("Smith");
+    QProperty<int> age(41);
+
+    QProperty<QString> fullname;
+    fullname.setBinding([&]() { return firstname.value() + " " + lastname.value() + " age:" + QString::number(age.value()); });
+
+    qDebug() << fullname.value(); // Prints "John Smith age: 41"
+
+    firstname = "Emma"; // Marks binding expression as dirty
+
+    qDebug() << fullname.value(); // Re-evaluates the binding expression and prints "Emma Smith age: 41"
+
+    // Birthday is coming up
+    age.setValue(age.value() + 1);
+
+    qDebug() << fullname.value(); // Re-evaluates the binding expression and prints "Emma Smith age: 42"
+  \endcode
+
+  When a new value is assigned to the \c firstname property, the binding
+  expression for \c fullname is marked as dirty. So when the last \c qDebug() statement
+  tries to read the name value of the \c fullname property, the expression is
+  evaluated again, \c firstname() will be called again and return the new value.
+
+  Since bindings are C++ lambda expressions, they may do anything that's possible
+  in C++. This includes calling other functions. If those functions access values
+  held by QProperty, they automatically become dependencies to the binding.
+
+  Binding expressions may use properties of any type, so in the above example the age
+  is an integer and folded into the string value using conversion to integer, but
+  the dependency is fully tracked.
+
+  \section1 Tracking properties
+
+  Sometimes the relationships between properties cannot be expressed using
+  bindings. Instead you may need to run custom code whenever the value of a property
+  changes and instead of assigning the value to another property, pass it to
+  other parts of your application. For example writing data into a network socket
+  or printing debug output. QProperty provides two mechanisms for tracking.
+
+  You can register for a callback function to be called whenever the value of
+  a property changes, by using onValueChanged(). If you want the callback to also
+  be called for the current value of the property, register your callback using
+  subscribe() instead.
+*/
+
+/*!
+  \fn template <typename T> QProperty<T>::QProperty()
+
+  Constructs a property with a default constructed instance of T.
+*/
+
+/*!
+  \fn template <typename T> explicit QProperty<T>::QProperty(const T &initialValue)
+
+  Constructs a property with the provided \a initialValue.
+*/
+
+/*!
+  \fn template <typename T> explicit QProperty<T>::QProperty(T &&initialValue)
+
+  Move-Constructs a property with the provided \a initialValue.
+*/
+
+/*!
+  \fn template <typename T> QProperty<T>::QProperty(QProperty<T> &&other)
+
+  Move-constructs a QProperty instance, making it point at the same object that
+  \a other was pointing to.
+*/
+
+/*!
+  \fn template <typename T> QProperty<T> &QProperty<T>::operator=(QProperty &&other)
+
+  Move-assigns \a other to this QProperty instance.
+*/
+
+/*!
+  \fn template <typename T> QProperty<T>::QProperty(const QPropertyBinding<T> &binding)
+
+  Constructs a property that is tied to the provided \a binding expression. The
+  first time the property value is read, the binding is evaluated. Whenever a
+  dependency of the binding changes, the binding will be re-evaluated the next
+  time the value of this property is read.
+*/
+
+/*!
+  \fn template <typename T> template <typename Functor> QProperty<T>::QProperty(Functor &&f)
+
+  Constructs a property that is tied to the provided binding expression \a f. The
+  first time the property value is read, the binding is evaluated. Whenever a
+  dependency of the binding changes, the binding will be re-evaluated the next
+  time the value of this property is read.
+*/
+
+/*!
+  \fn template <typename T> QProperty<T>::~QProperty()
+
+  Destroys the property.
+*/
+
+/*!
+  \fn template <typename T> T QProperty<T>::value() const
+
+  Returns the value of the property. This may evaluate a binding expression that
+  is tied to this property, before returning the value.
+*/
+
+/*!
+  \fn template <typename T> QProperty<T>::operator T() const
+
+  Returns the value of the property. This may evaluate a binding expression that
+  is tied to this property, before returning the value.
+*/
+
+/*!
+  \fn template <typename T> void QProperty<T>::setValue(const T &newValue)
+
+  Assigns \a newValue to this property and removes the property's associated
+  binding, if present.
+*/
+
+/*!
+  \fn template <typename T> void QProperty<T>::setValue(T &&newValue)
+  \overload
+
+  Assigns \a newValue to this property and removes the property's associated
+  binding, if present.
+*/
+
+/*!
+  \fn template <typename T> QProperty<T> &QProperty<T>::operator=(const T &newValue)
+
+  Assigns \a newValue to this property and returns a reference to this QProperty.
+*/
+
+/*!
+  \fn template <typename T> QProperty<T> &QProperty<T>::operator=(T &&newValue)
+  \overload
+
+  Assigns \a newValue to this property and returns a reference to this QProperty.
+*/
+
+/*!
+  \fn template <typename T> QProperty<T> &QProperty<T>::operator=(const QPropertyBinding<T> &newBinding)
+
+  Associates the value of this property with the provided \a newBinding
+  expression and returns a reference to this property. The first time the
+  property value is read, the binding is evaluated. Whenever a dependency of the
+  binding changes, the binding will be re-evaluated the next time the value of
+  this property is read.
+*/
+
+/*!
+  \fn template <typename T> QPropertyBinding<T> QProperty<T>::setBinding(const QPropertyBinding<T> &newBinding)
+
+  Associates the value of this property with the provided \a newBinding
+  expression and returns the previously associated binding. The first time the
+  property value is read, the binding is evaluated. Whenever a dependency of the
+  binding changes, the binding will be re-evaluated the next time the value of
+  this property is read.
+*/
+
+/*!
+  \fn template <typename T> template <typename Functor> QPropertyBinding<T> QProperty<T>::setBinding(Functor f)
+  \overload
+
+  Associates the value of this property with the provided functor \a f and
+  returns the previously associated binding. The first time the property value
+  is read, the binding is evaluated by invoking the call operator () of \a f.
+  Whenever a dependency of the binding changes, the binding will be re-evaluated
+  the next time the value of this property is read.
+*/
+
+/*!
+  \fn template <typename T> QPropertyBinding<T> QProperty<T>::setBinding(QPropertyBinding<T> &&newBinding)
+  \overload
+
+  Associates the value of this property with the provided \a newBinding
+  expression and returns the previously associated binding. The first time the
+  property value is read, the binding is evaluated. Whenever a dependency of the
+  binding changes, the binding will be re-evaluated the next time the value of
+  this property is read.
+*/
+
+/*!
+  \fn template <typename T> QPropertyBinding<T> QProperty<T>::binding() const
+
+  Returns the binding expression that is associated with this property. A
+  default constructed QPropertyBinding<T> will be returned if no such
+  association exists.
+*/
+
+/*!
+  \fn template <typename T> QPropertyBinding<T> QProperty<T>::takeBinding()
+
+  Disassociates the binding expression from this property and returns it. After
+  calling this function, the value of the property will only change if you
+  assign a new value to it, or when a new binding is set.
+*/
+
+/*!
+  \fn template <typename T> template <typename Functor> QPropertyChangeHandler<T, Functor> QProperty<T>::onValueChanged(Functor f)
+
+  Registers the given functor \a f as a callback that shall be called whenever
+  the value of the property changes.
+
+  The callback \a f is expected to be a type that has a plain call operator () without any
+  parameters. This means that you can provide a C++ lambda expression, an std::function
+  or even a custom struct with a call operator.
+
+  The returned property change handler object keeps track of the registration. When it
+  goes out of scope, the callback is de-registered.
+*/
+
+/*!
+  \fn template <typename T> template <typename Functor> QPropertyChangeHandler<T, Functor> QProperty<T>::subscribe(Functor f)
+
+  Subscribes the given functor \a f as a callback that is called immediately and whenever
+  the value of the property changes in the future.
+
+  The callback \a f is expected to be a type that has a plain call operator () without any
+  parameters. This means that you can provide a C++ lambda expression, an std::function
+  or even a custom struct with a call operator.
+
+  The returned property change handler object keeps track of the subscription. When it
+  goes out of scope, the callback is unsubscribed.
+*/
+
+/*!
+  \class QPropertyChangeHandler
+  \inmodule QtCore
+  \brief The QPropertyChangeHandler class controls the lifecycle of change callback installed on a QProperty.
+
+  \ingroup tools
+
+  QPropertyChangeHandler\<PropertyType, Functor\> is created when registering a
+  callback on a QProperty to listen to changes to the property's value, using QProperty::onValueChanged
+  and QProperty::subscribe. As long as the change handler is alive, the callback remains installed.
+
+  A handler instance can be transferred between C++ scopes using move semantics.
+*/
+
+QT_END_NAMESPACE