From 240505457bb1e8280682c7274493a7a6f61a1045 Mon Sep 17 00:00:00 2001
From: Fabian Kosmale <fabian.kosmale@qt.io>
Date: Tue, 15 Dec 2020 11:09:16 +0100
Subject: [PATCH] QBindable: Improve read-only support

If we create a QBindable from a const property, we should obtain a
read-only interface. Besides implementing this feature, this patch adds
a isReadOnly method to Q(Untyped)Bindable which can be used to check
whether one can modify the property via the bindable interface.

Task-number: QTBUG-89505
Task-number: QTBUG-89469
Change-Id: Ic36949a5b84c5119e0060ed0a1cf4ac94a66f341
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
---
 src/corelib/kernel/qproperty.h                | 25 ++++++++++++++++++-
 .../kernel/qproperty/tst_qproperty.cpp        |  8 ++++++
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/src/corelib/kernel/qproperty.h b/src/corelib/kernel/qproperty.h
index 8fda7715c2..f853eb8634 100644
--- a/src/corelib/kernel/qproperty.h
+++ b/src/corelib/kernel/qproperty.h
@@ -494,7 +494,7 @@ class QBindableInterfaceForProperty
 {
     using T = typename Property::value_type;
 public:
-    // interface for read-only properties. Those do not have a binding()/setBinding() method, but one can
+    // interface for computed properties. Those do not have a binding()/setBinding() method, but one can
     // install observers on them.
     static constexpr QBindableInterface iface = {
         [](const QUntypedPropertyData *d, void *value) -> void
@@ -510,6 +510,28 @@ public:
     };
 };
 
+template<typename Property>
+class QBindableInterfaceForProperty<const Property, std::void_t<decltype(std::declval<Property>().binding())>>
+{
+    using T = typename Property::value_type;
+public:
+    // A bindable created from a const property results in a read-only interface, too.
+    static constexpr QBindableInterface iface = {
+
+        [](const QUntypedPropertyData *d, void *value) -> void
+        { *static_cast<T*>(value) = static_cast<const Property *>(d)->value(); },
+        /*setter=*/nullptr,
+        [](const QUntypedPropertyData *d) -> QUntypedPropertyBinding
+        { return static_cast<const Property *>(d)->binding(); },
+        /*setBinding=*/nullptr,
+        [](const QUntypedPropertyData *d, const QPropertyBindingSourceLocation &location) -> QUntypedPropertyBinding
+        { return Qt::makePropertyBinding([d]() -> T { return static_cast<const Property *>(d)->value(); }, location); },
+        [](const QUntypedPropertyData *d, QPropertyObserver *observer) -> void
+        { observer->setSource(static_cast<const Property *>(d)->bindingData()); },
+        []() { return QMetaType::fromType<T>(); }
+    };
+};
+
 template<typename Property>
 class QBindableInterfaceForProperty<Property, std::void_t<decltype(std::declval<Property>().binding())>>
 {
@@ -553,6 +575,7 @@ public:
 
     bool isValid() const { return data != nullptr; }
     bool isBindable() const { return iface && iface->getBinding; }
+    bool isReadOnly() const { return !(iface && iface->setBinding && iface->setObserver); }
 
     QUntypedPropertyBinding makeBinding(const QPropertyBindingSourceLocation &location = QT_PROPERTY_DEFAULT_BINDING_LOCATION)
     {
diff --git a/tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp b/tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp
index 4559587afd..7de6458406 100644
--- a/tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp
+++ b/tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp
@@ -1048,6 +1048,7 @@ public:
     }
 
     QBindable<int> bindableFoo() { return QBindable<int>(&fooData); }
+    const QBindable<int> bindableFoo() const { return QBindable<int>(&fooData); }
     QBindable<int> bindableBar() { return QBindable<int>(&barData); }
     QBindable<int> bindableRead() { return QBindable<int>(&readData); }
     QBindable<int> bindableComputed() { return QBindable<int>(&computedData); }
@@ -1068,7 +1069,14 @@ public:
 
 void tst_QProperty::testNewStuff()
 {
+    MyQObject testReadOnly;
+    testReadOnly.bindableFoo().setBinding([](){return 42;});
+    auto bindable = const_cast<const MyQObject&>(testReadOnly).bindableFoo();
+    QVERIFY(bindable.hasBinding());
+    QVERIFY(bindable.isReadOnly());
+
     MyQObject object;
+    QVERIFY(!object.bindableFoo().isReadOnly());
     QObject::connect(&object, &MyQObject::fooChanged, &object, &MyQObject::fooHasChanged);
     QObject::connect(&object, &MyQObject::barChanged, &object, &MyQObject::barHasChanged);