QHostInfoResult: use the same semantics as the contextless connect()

The 3-arg QObject::connect() overload (the "contextless" one) simply
forwards to the 4-arg overload, using the sender object as both
the sender and the receiver/context.

QHostInfo does not use connect() directly in order to emit notifications
that a lookup is finished. Instead, it uses some of QObject private
plumbing. When handling a lookup request that specifies a function
to call when done, but no context object, QHostInfo passes nullptr
as context/receiver.

Change QHostInfoResult's behavior to always have a "receiver": in case
the caller didn't specify one, use `this` (= the sender).
As a drive-by, this allows to streamline some code.

Change-Id: Ic2e63ac18ba36269036950b6f6b7fecea51d0c99
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

2 files changed, 14 insertions, 11 deletions

diff --git a/src/network/kernel/qhostinfo.cpp b/src/network/kernel/qhostinfo.cpp
index 6662ae1eee..dab4d055ed 100644
--- a/src/network/kernel/qhostinfo.cpp
+++ b/src/network/kernel/qhostinfo.cpp
@@ -73,10 +73,10 @@ Q_APPLICATION_STATIC(QHostInfoLookupManager, theHostInfoLookupManager)
 }
 
 QHostInfoResult::QHostInfoResult(const QObject *receiver, QtPrivate::SlotObjUniquePtr slot)
-    : receiver{receiver}, slotObj{std::move(slot)}, withContextObject{slotObj && receiver}
+    : receiver{receiver ? receiver : this}, slotObj{std::move(slot)}
 {
-    if (receiver)
-        moveToThread(receiver->thread());
+    Q_ASSERT(this->receiver);
+    moveToThread(this->receiver->thread());
 }
 
 QHostInfoResult::~QHostInfoResult()
@@ -101,7 +101,7 @@ void QHostInfoResult::postResultsReady(const QHostInfo &info)
         return;
     }
     // we used to have a context object, but it's already destroyed
-    if (withContextObject && !receiver)
+    if (!receiver)
         return;
 
     static const int signal_index = []() -> int {
@@ -129,11 +129,13 @@ bool QHostInfoResult::event(QEvent *event)
 {
     if (event->type() == QEvent::MetaCall) {
         Q_ASSERT(slotObj);
-        auto metaCallEvent = static_cast<QMetaCallEvent *>(event);
-        auto args = metaCallEvent->args();
-        // we didn't have a context object, or it's still alive
-        if (!withContextObject || receiver)
+
+        // we used to have a context object, but it's already destroyed
+        if (receiver) {
+            auto metaCallEvent = static_cast<QMetaCallEvent *>(event);
+            auto args = metaCallEvent->args();
             slotObj->call(const_cast<QObject*>(receiver.data()), args);
+        }
 
         deleteLater();
         return true;
diff --git a/src/network/kernel/qhostinfo_p.h b/src/network/kernel/qhostinfo_p.h
index 70cacc6b3d..4c0d5010fc 100644
--- a/src/network/kernel/qhostinfo_p.h
+++ b/src/network/kernel/qhostinfo_p.h
@@ -56,8 +56,8 @@ protected:
 
 private:
     QHostInfoResult(const QHostInfoResult *other)
-        : receiver(other->receiver), slotObj{copy(other->slotObj)},
-          withContextObject(other->withContextObject)
+        : receiver(other->receiver.get() != other ? other->receiver.get() : this),
+          slotObj{copy(other->slotObj)}
     {
         // cleanup if the application terminates before results are delivered
         connect(QCoreApplication::instance(), &QCoreApplication::aboutToQuit,
@@ -66,9 +66,10 @@ private:
         moveToThread(other->thread());
     }
 
+    // receiver is either a QObject provided by the user,
+    // or it's set to `this` (to emulate the behavior of the contextless connect())
     QPointer<const QObject> receiver = nullptr;
     QtPrivate::SlotObjUniquePtr slotObj;
-    const bool withContextObject = false;
 };
 
 class QHostInfoAgent