Don't declare type 'id' in the global namespace in a public header

It's not necessary, and it breaks the qttools build (where we have a
global variable named 'id'), and thus will most certainly build a lot
of existing user code.

Amends e47c22480fe84c100019cd92d0296f0dd2a7f3f1.

Change-Id: I97a91c2cb23fdae65143cf14c81570cf88d529d5
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/corelib/io/qdebug.h

@@ -530,7 +530,7 @@ inline QDebug operator<<(QDebug debug, QKeyCombination combination)
 
 QT_END_NAMESPACE
 Q_FORWARD_DECLARE_CF_TYPE(CFString);
-typedef struct objc_object *id;
+struct objc_object;
 Q_FORWARD_DECLARE_OBJC_CLASS(NSObject);
 QT_FOR_EACH_CORE_FOUNDATION_TYPE(QT_FORWARD_DECLARE_CF_TYPE)
 QT_FOR_EACH_MUTABLE_CORE_FOUNDATION_TYPE(QT_FORWARD_DECLARE_MUTABLE_CF_TYPE)
@@ -555,7 +555,10 @@ QT_BEGIN_NAMESPACE
     }
 
 // Defined in qcore_mac_objc.mm
-Q_CORE_EXPORT QDebug operator<<(QDebug, id obj);
+#if defined(__OBJC__)
+Q_CORE_EXPORT QDebug operator<<(QDebug, id);
+#endif
+Q_CORE_EXPORT QDebug operator<<(QDebug, objc_object *);
 Q_CORE_EXPORT QDebug operator<<(QDebug, const NSObject *);
 Q_CORE_EXPORT QDebug operator<<(QDebug, CFStringRef);
 

tests/auto/corelib/io/qdebug/CMakeLists.txt

@@ -10,3 +10,7 @@ qt_internal_add_test(tst_qdebug
     PUBLIC_LIBRARIES
         Qt::Concurrent
 )
+
+if (APPLE)
+    target_compile_options(tst_qdebug PRIVATE -x objective-c++)
+endif()

tests/auto/corelib/io/qdebug/tst_qdebug.cpp

@@ -52,6 +52,10 @@ struct ConvertsToQVariant {
 };
 static_assert(!QTypeTraits::has_ostream_operator_v<QDebug, ConvertsToQVariant>);
 
+#if defined(Q_OS_DARWIN)
+#include <objc/runtime.h>
+#include <Foundation/Foundation.h>
+#endif
 
 class tst_QDebug: public QObject
 {
@@ -88,6 +92,12 @@ private slots:
     void threadSafety() const;
     void toString() const;
     void noQVariantEndlessRecursion() const;
+#if defined(Q_OS_DARWIN)
+    void objcInCppMode_data() const;
+    void objcInCppMode() const;
+    void objcInObjcMode_data() const;
+    void objcInObjcMode() const;
+#endif
 };
 
 void tst_QDebug::assignment() const
@@ -873,6 +883,69 @@ void tst_QDebug::noQVariantEndlessRecursion() const
     qDebug() << var;
 }
 
+#if defined(Q_OS_DARWIN)
+
+@interface MyObjcClass : NSObject
+@end
+
+@implementation MyObjcClass : NSObject
+- (NSString *)description
+{
+    return @"MyObjcClass is the best";
+}
+@end
+
+void tst_QDebug::objcInCppMode_data() const
+{
+    QTest::addColumn<objc_object *>("object");
+    QTest::addColumn<QString>("message");
+
+    QTest::newRow("nil") << static_cast<objc_object*>(nullptr) << QString::fromLatin1("(null)");
+
+    // Not an NSObject subclass
+    auto *nsproxy = reinterpret_cast<objc_object *>(class_createInstance(objc_getClass("NSProxy"), 0));
+    QTest::newRow("NSProxy") << nsproxy << QString::fromLatin1("<NSProxy: 0x%1>").arg(uintptr_t(nsproxy), 1, 16);
+
+    // Plain NSObject
+    auto *nsobject = reinterpret_cast<objc_object *>(class_createInstance(objc_getClass("NSObject"), 0));
+    QTest::newRow("NSObject") << nsobject << QString::fromLatin1("<NSObject: 0x%1>").arg(uintptr_t(nsobject), 1, 16);
+
+    auto str = QString::fromLatin1("foo");
+    QTest::newRow("NSString") << reinterpret_cast<objc_object*>(str.toNSString()) << str;
+
+    // Custom debug description
+    QTest::newRow("MyObjcClass") << reinterpret_cast<objc_object*>([[MyObjcClass alloc] init])
+                                 << QString::fromLatin1("MyObjcClass is the best");
+}
+
+void tst_QDebug::objcInCppMode() const
+{
+    QFETCH(objc_object *, object);
+    QFETCH(QString, message);
+
+    MessageHandlerSetter mhs(myMessageHandler);
+    { qDebug() << object; }
+
+    QCOMPARE(s_msg, message);
+}
+
+void tst_QDebug::objcInObjcMode_data() const
+{
+    objcInCppMode_data();
+}
+
+void tst_QDebug::objcInObjcMode() const
+{
+    QFETCH(objc_object *, object);
+    QFETCH(QString, message);
+
+    MessageHandlerSetter mhs(myMessageHandler);
+    { qDebug() << static_cast<id>(object); }
+
+    QCOMPARE(s_msg, message);
+}
+#endif
+
 // Should compile: instentiation of unrelated operator<< should not cause cause compilation
 // error in QDebug operators (QTBUG-47375)
 class TestClassA {};