use boolean for when property

QQuickState used to store "when" as a QQmlBinding to reduce state
oscillation.

It is unclear whether this is still an issue, but it breaks if a user
sets "when" to a primitive value like "true" or "1".

Fixes: QTBUG-76838
Change-Id: If400e5b1283687838ed252be2dfa52067f44564e
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

6 files changed, 28 insertions, 14 deletions

diff --git a/src/quick/util/qquickstate.cpp b/src/quick/util/qquickstate.cpp
index 3ca6440784..473539ab2c 100644
--- a/src/quick/util/qquickstate.cpp
+++ b/src/quick/util/qquickstate.cpp
@@ -192,7 +192,7 @@ bool QQuickState::isNamed() const
 bool QQuickState::isWhenKnown() const
 {
     Q_D(const QQuickState);
-    return d->when != nullptr;
+    return d->whenKnown;
 }
 
 /*!
@@ -219,15 +219,16 @@ bool QQuickState::isWhenKnown() const
     }
     \endqml
 */
-QQmlBinding *QQuickState::when() const
+bool QQuickState::when() const
 {
     Q_D(const QQuickState);
-    return d->when.data();
+    return d->when;
 }
 
-void QQuickState::setWhen(QQmlBinding *when)
+void QQuickState::setWhen(bool when)
 {
     Q_D(QQuickState);
+    d->whenKnown = true;
     d->when = when;
     if (d->group)
         d->group->updateAutoState();
diff --git a/src/quick/util/qquickstate_p.h b/src/quick/util/qquickstate_p.h
index 79874ee78e..576ba9834c 100644
--- a/src/quick/util/qquickstate_p.h
+++ b/src/quick/util/qquickstate_p.h
@@ -152,7 +152,7 @@ class Q_QUICK_PRIVATE_EXPORT QQuickState : public QObject
     Q_OBJECT
 
     Q_PROPERTY(QString name READ name WRITE setName)
-    Q_PROPERTY(QQmlBinding *when READ when WRITE setWhen)
+    Q_PROPERTY(bool when READ when WRITE setWhen)
     Q_PROPERTY(QString extend READ extends WRITE setExtends)
     Q_PROPERTY(QQmlListProperty<QQuickStateOperation> changes READ changes)
     Q_CLASSINFO("DefaultProperty", "changes")
@@ -166,11 +166,9 @@ public:
     void setName(const QString &);
     bool isNamed() const;
 
-    /*'when' is a QQmlBinding to limit state changes oscillation
-     due to the unpredictable order of evaluation of bound expressions*/
     bool isWhenKnown() const;
-    QQmlBinding *when() const;
-    void setWhen(QQmlBinding *);
+    bool when() const;
+    void setWhen(bool);
 
     QString extends() const;
     void setExtends(const QString &);
diff --git a/src/quick/util/qquickstate_p_p.h b/src/quick/util/qquickstate_p_p.h
index 61472b4d06..70d6f1d185 100644
--- a/src/quick/util/qquickstate_p_p.h
+++ b/src/quick/util/qquickstate_p_p.h
@@ -203,12 +203,13 @@ class QQuickStatePrivate : public QObjectPrivate
 
 public:
     QQuickStatePrivate()
-    : named(false), inState(false), group(nullptr) {}
+        : when(false), whenKnown(false), named(false), inState(false), group(nullptr) {}
 
     typedef QList<QQuickSimpleAction> SimpleActionList;
 
     QString name;
-    QQmlBinding::Ptr when;
+    bool when;
+    bool whenKnown;
     bool named;
 
     struct OperationGuard : public QQmlGuard<QQuickStateOperation>
diff --git a/src/quick/util/qquickstategroup.cpp b/src/quick/util/qquickstategroup.cpp
index b53949d21c..0adae82dcc 100644
--- a/src/quick/util/qquickstategroup.cpp
+++ b/src/quick/util/qquickstategroup.cpp
@@ -348,10 +348,9 @@ bool QQuickStateGroupPrivate::updateAutoState()
         QQuickState *state = states.at(ii);
         if (state->isWhenKnown()) {
             if (state->isNamed()) {
-                if (state->when() && state->when()->evaluate().toBool()) {
+                if (state->when()) {
                     if (stateChangeDebug())
-                        qWarning() << "Setting auto state due to:"
-                                   << state->when()->expression();
+                        qWarning() << "Setting auto state due to expression";
                     if (currentState != state->name()) {
                         q->setState(state->name());
                         return true;
diff --git a/tests/auto/quick/qquickstates/data/trivialWhen.qml b/tests/auto/quick/qquickstates/data/trivialWhen.qml
new file mode 100644
index 0000000000..9f7f3161e9
--- /dev/null
+++ b/tests/auto/quick/qquickstates/data/trivialWhen.qml
@@ -0,0 +1,5 @@
+import QtQuick 2.12
+
+State {
+    when: true
+}
diff --git a/tests/auto/quick/qquickstates/tst_qquickstates.cpp b/tests/auto/quick/qquickstates/tst_qquickstates.cpp
index 50554f6333..1eb797f54f 100644
--- a/tests/auto/quick/qquickstates/tst_qquickstates.cpp
+++ b/tests/auto/quick/qquickstates/tst_qquickstates.cpp
@@ -138,6 +138,7 @@ private slots:
     void QTBUG_38492();
     void revertListMemoryLeak();
     void duplicateStateName();
+    void trivialWhen();
 };
 
 void tst_qquickstates::initTestCase()
@@ -1665,6 +1666,15 @@ void tst_qquickstates::duplicateStateName()
     QVERIFY(!item.isNull());
 }
 
+// QTBUG-76838
+void tst_qquickstates::trivialWhen()
+{
+    QQmlEngine engine;
+
+    QQmlComponent c(&engine, testFileUrl("trivialWhen.qml"));
+    QVERIFY(c.create());
+}
+
 
 QTEST_MAIN(tst_qquickstates)