QPrinterInfo - Fix isNull() by fixing constructors

The QPrinterInfo copy and QPrinter constructors and the assignment
operator were not taking the shared_null into account, and so any use
of them resulted in a new null QPrinterInfo different to shared_null,
which lead to isNull() always returning true in anything other than
the simplest use case. While fixing this also make the shared_null a
Q_GLOBAL_STATIC.

Task-number: QTBUG-21087

Change-Id: I0beb24088208e9ed58d21ca26b0c8d00b02e5b8f
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>

src/printsupport/kernel/qprinterinfo.cpp

@@ -35,8 +35,17 @@
 
 QT_BEGIN_NAMESPACE
 
-QPrinterInfoPrivate QPrinterInfoPrivate::shared_null;
+Q_GLOBAL_STATIC(QPrinterInfoPrivate, shared_null);
 
+class QPrinterInfoPrivateDeleter
+{
+public:
+    static inline void cleanup(QPrinterInfoPrivate *d)
+    {
+        if (d != shared_null)
+            delete d;
+    }
+};
 
 /*!
     \class QPrinterInfo
@@ -83,7 +92,7 @@ QPrinterInfoPrivate QPrinterInfoPrivate::shared_null;
     \sa isNull()
 */
 QPrinterInfo::QPrinterInfo()
-    : d_ptr(&QPrinterInfoPrivate::shared_null)
+    : d_ptr(shared_null)
 {
 }
 
@@ -91,7 +100,7 @@ QPrinterInfo::QPrinterInfo()
     Constructs a copy of \a other.
 */
 QPrinterInfo::QPrinterInfo(const QPrinterInfo &other)
-    : d_ptr(new QPrinterInfoPrivate(*other.d_ptr))
+    : d_ptr((other.d_ptr.data() == shared_null) ? shared_null : new QPrinterInfoPrivate(*other.d_ptr))
 {
 }
 
@@ -99,12 +108,15 @@ QPrinterInfo::QPrinterInfo(const QPrinterInfo &other)
     Constructs a QPrinterInfo object from \a printer.
 */
 QPrinterInfo::QPrinterInfo(const QPrinter &printer)
-    : d_ptr(&QPrinterInfoPrivate::shared_null)
+    : d_ptr(shared_null)
 {
     QPlatformPrinterSupport *ps = QPlatformPrinterSupportPlugin::get();
     if (ps) {
         QPrinterInfo pi = ps->printerInfo(printer.printerName());
-        d_ptr.reset(new QPrinterInfoPrivate(*pi.d_ptr));
+        if (pi.d_ptr.data() == shared_null)
+            d_ptr.reset(shared_null);
+        else
+            d_ptr.reset(new QPrinterInfoPrivate(*pi.d_ptr));
     }
 }
 
@@ -130,7 +142,10 @@ QPrinterInfo::~QPrinterInfo()
 QPrinterInfo &QPrinterInfo::operator=(const QPrinterInfo &other)
 {
     Q_ASSERT(d_ptr);
-    d_ptr.reset(new QPrinterInfoPrivate(*other.d_ptr));
+    if (other.d_ptr.data() == shared_null)
+        d_ptr.reset(shared_null);
+    else
+        d_ptr.reset(new QPrinterInfoPrivate(*other.d_ptr));
     return *this;
 }
 
@@ -191,7 +206,7 @@ QString QPrinterInfo::makeAndModel() const
 bool QPrinterInfo::isNull() const
 {
     Q_D(const QPrinterInfo);
-    return d == &QPrinterInfoPrivate::shared_null;
+    return d == shared_null || d->name.isEmpty();
 }
 
 /*!

src/printsupport/kernel/qprinterinfo_p.h

@@ -72,8 +72,6 @@ public:
     ~QPrinterInfoPrivate()
     {}
 
-    static QPrinterInfoPrivate shared_null;
-
     QString name;
     QString description;
     QString location;
@@ -87,17 +85,6 @@ public:
     mutable QList<QPair<QString, QSizeF> > paperNames;
 };
 
-
-class QPrinterInfoPrivateDeleter
-{
-public:
-    static inline void cleanup(QPrinterInfoPrivate *d)
-    {
-        if (d != &QPrinterInfoPrivate::shared_null)
-            delete d;
-    }
-};
-
 QT_END_NAMESPACE
 
 #endif // QT_NO_PRINTER

tests/auto/printsupport/kernel/qprinterinfo/tst_qprinterinfo.cpp

@@ -275,6 +275,9 @@ void tst_QPrinterInfo::testConstructors()
     QCOMPARE(null.printerName(), QString());
     QVERIFY(null.isNull());
 
+    QPrinterInfo null2(null);
+    QVERIFY(null2.isNull());
+
     QList<QPrinterInfo> printers = QPrinterInfo::availablePrinters();
 
     for (int i = 0; i < printers.size(); ++i) {
@@ -295,6 +298,12 @@ void tst_QPrinterInfo::testConstructors()
 
 void tst_QPrinterInfo::testAssignment()
 {
+    QPrinterInfo null;
+    QVERIFY(null.isNull());
+    QPrinterInfo null2;
+    null2 = null;
+    QVERIFY(null2.isNull());
+
     QList<QPrinterInfo> printers = QPrinterInfo::availablePrinters();
 
     for (int i = 0; i < printers.size(); ++i) {