Use qt.qml.states logging category instead of STATECHANGE_DEBUG env

- It should not be a warning: it's for debugging.
- It's nice to have the logging category instead of "default" in case
  you have %{category} in your QT_MESSAGE_PATTERN.
- The env var didn't even have QT or QML in it.

[ChangeLog][QtQml] The new qt.qml.states logging category is useful
for debugging states and transitions. It replaces the STATECHANGE_DEBUG
environment variable.

Task-number: QTBUG-100117
Change-Id: If67e21488a66867645f3a395941fcc92d3ea7bbb
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
(cherry picked from commit 3fc68053db3acd9f7bef23d3aef1f7ac874e73dc)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

3 files changed, 19 insertions, 24 deletions

diff --git a/src/quick/util/qquickstate.cpp b/src/quick/util/qquickstate.cpp
index bd563e34b8..735b5267f7 100644
--- a/src/quick/util/qquickstate.cpp
+++ b/src/quick/util/qquickstate.cpp
@@ -49,7 +49,7 @@
 
 QT_BEGIN_NAMESPACE
 
-DEFINE_BOOL_CONFIG_OPTION(stateChangeDebug, STATECHANGE_DEBUG);
+Q_LOGGING_CATEGORY(lcStates, "qt.qml.states")
 
 QQuickStateAction::QQuickStateAction()
 : restore(true), actionDone(false), reverseEvent(false), deletableToBinding(false), fromBinding(nullptr), event(nullptr),
@@ -671,19 +671,16 @@ void QQuickState::apply(QQuickTransition *trans, QQuickState *revert)
     // All the local reverts now become part of the ongoing revertList
     d->revertList << additionalReverts;
 
-#ifndef QT_NO_DEBUG_STREAM
-    // Output for debugging
-    if (stateChangeDebug()) {
+    if (lcStates().isDebugEnabled()) {
         for (const QQuickStateAction &action : qAsConst(applyList)) {
             if (action.event)
-                qWarning() << "    QQuickStateAction event:" << action.event->type();
+                qCDebug(lcStates) << "QQuickStateAction event:" << action.event->type();
             else
-                qWarning() << "    QQuickStateAction:" << action.property.object()
-                           << action.property.name() << "From:" << action.fromValue
-                           << "To:" << action.toValue;
+                qCDebug(lcStates) << "QQuickStateAction on" << action.property.object()
+                                  << action.property.name() << "from:" << action.fromValue
+                                  << "to:" << action.toValue;
         }
     }
-#endif
 
     d->transitionManager.transition(applyList, trans);
 }
diff --git a/src/quick/util/qquickstategroup.cpp b/src/quick/util/qquickstategroup.cpp
index b86333943c..d664b67485 100644
--- a/src/quick/util/qquickstategroup.cpp
+++ b/src/quick/util/qquickstategroup.cpp
@@ -53,7 +53,7 @@
 
 QT_BEGIN_NAMESPACE
 
-DEFINE_BOOL_CONFIG_OPTION(stateChangeDebug, STATECHANGE_DEBUG);
+Q_DECLARE_LOGGING_CATEGORY(lcStates)
 
 class QQuickStateGroupPrivate : public QObjectPrivate
 {
@@ -377,8 +377,7 @@ bool QQuickStateGroupPrivate::updateAutoState()
         if (state->isWhenKnown()) {
             if (state->isNamed()) {
                 if (state->when()) {
-                    if (stateChangeDebug())
-                        qWarning() << "Setting auto state due to expression";
+                    qCDebug(lcStates) << "Setting auto state due to expression";
                     if (currentState != state->name()) {
                         q->setState(state->name());
                         return true;
@@ -483,11 +482,11 @@ void QQuickStateGroupPrivate::setCurrentStateInternal(const QString &state,
     applyingState = true;
 
     QQuickTransition *transition = ignoreTrans ? nullptr : findTransition(currentState, state);
-    if (stateChangeDebug()) {
-        qWarning() << this << "Changing state.  From" << currentState << ". To" << state;
+    if (lcStates().isDebugEnabled()) {
+        qCDebug(lcStates) << this << "changing state from:" << currentState << "to:" << state;
         if (transition)
-            qWarning() << "   using transition" << transition->fromState()
-                       << transition->toState();
+            qCDebug(lcStates) << "   using transition" << transition->fromState()
+                              << transition->toState();
     }
 
     QQuickState *oldState = nullptr;
diff --git a/src/quick/util/qquicktransitionmanager.cpp b/src/quick/util/qquicktransitionmanager.cpp
index 97c1fcd045..6784ad83d6 100644
--- a/src/quick/util/qquicktransitionmanager.cpp
+++ b/src/quick/util/qquicktransitionmanager.cpp
@@ -51,7 +51,7 @@
 
 QT_BEGIN_NAMESPACE
 
-DEFINE_BOOL_CONFIG_OPTION(stateChangeDebug, STATECHANGE_DEBUG);
+Q_DECLARE_LOGGING_CATEGORY(lcStates)
 
 class QQuickTransitionManagerPrivate
 {
@@ -240,18 +240,17 @@ void QQuickTransitionManager::transition(const QList<QQuickStateAction> &list,
             action.property.write(action.toValue);
         }
     }
-#ifndef QT_NO_DEBUG_STREAM
-    if (stateChangeDebug()) {
+    if (lcStates().isDebugEnabled()) {
         for (const QQuickStateAction &action : qAsConst(applyList)) {
             if (action.event)
-                qWarning() << "    No transition for event:" << action.event->type();
+                qCDebug(lcStates) << "no transition for event:" << action.event->type();
             else
-                qWarning() << "    No transition for:" << action.property.object()
-                           << action.property.name() << "From:" << action.fromValue
-                           << "To:" << action.toValue;
+                qCDebug(lcStates) << "no transition for:" << action.property.object()
+                                  << action.property.name() << "from:" << action.fromValue
+                                  << "to:" << action.toValue;
         }
     }
-#endif
+
     if (!transition)
         complete();
 }