Provide D-Bus de-/marshalling operators for std::tuple

Currently Qt provides only generic operators for pairs which can be used
generically for structs with two elements. A tuple is the natural fit
for dealing generically with structs that have more elements.
This can be helpful when wanting to make a one-of calls to APIs that
take or return such types or deferring to tuple marshalling without
having to write custom operators.

[ChangeLog][QtDBus][QDBusArgument] Added generic support for
marshalling and demarshalling D-Bus STRUCTs from/to std::tuple.

Change-Id: Id5cf49063c9b43ed68ad7821111376f6fa887a73
Reviewed-by: Thiago Macieira <[email protected]>

src/dbus/doc/src/dbus-adaptors.qdoc

@@ -295,8 +295,9 @@
     Qt D-Bus provides template specializations for arrays and maps for
     use with Qt's \l{Container classes}{container classes}, such as
     QMap and QList, so it is not necessary to write the streaming
-    operator functions for those. For other types, and specially for
-    types implementing structures, the operators have to be explicitly
+    operator functions for those. For structures Qt provides generic
+    specializations mapping to and from \c std::tuple. In order to use
+    a custom type instead or for other types the operators have to be explicitly
     implemented.
 
     See the documentation for QDBusArgument for examples for

src/dbus/qdbusargument.h

@@ -321,6 +321,26 @@ inline const QDBusArgument &operator>>(const QDBusArgument &arg, std::pair<T1, T
     return arg;
 }
 
+template <typename... T>
+QDBusArgument &operator<<(QDBusArgument &argument, const std::tuple<T...> &tuple)
+{
+    static_assert(std::tuple_size_v<std::tuple<T...>> != 0, "D-Bus doesn't allow empty structs");
+    argument.beginStructure();
+    std::apply([&argument](const auto &...elements) { (argument << ... << elements); }, tuple);
+    argument.endStructure();
+    return argument;
+}
+
+template <typename... T>
+const QDBusArgument &operator>>(const QDBusArgument &argument, std::tuple<T...> &tuple)
+{
+    static_assert(std::tuple_size_v<std::tuple<T...>> != 0, "D-Bus doesn't allow empty structs");
+    argument.beginStructure();
+    std::apply([&argument](auto &...elements) { (argument >> ... >> elements); }, tuple);
+    argument.endStructure();
+    return argument;
+}
+
 QT_END_NAMESPACE
 
 #endif // QT_NO_DBUS

tests/auto/dbus/qdbusmarshall/common.h

@@ -160,6 +160,14 @@ void commonInit()
     qDBusRegisterMetaType<QList<MyVariantMapStruct> >();
     qDBusRegisterMetaType<MyFileDescriptorStruct>();
     qDBusRegisterMetaType<QList<MyFileDescriptorStruct> >();
+
+    qDBusRegisterMetaType<std::tuple<int>>();
+    qDBusRegisterMetaType<std::tuple<QString>>();
+    qDBusRegisterMetaType<std::tuple<QVariantMap>>();
+    qDBusRegisterMetaType<std::tuple<QPoint>>();
+    qDBusRegisterMetaType<std::tuple<std::tuple<int>>>();
+    qDBusRegisterMetaType<std::tuple<QList<int>>>();
+    qDBusRegisterMetaType<std::tuple<int, QString, QVariantMap>>();
 }
 #ifdef USE_PRIVATE_CODE
 #include "private/qdbusintrospection_p.h"
@@ -510,6 +518,21 @@ bool compareToArgument(const QDBusArgument &arg, const QVariant &v2)
             return compare<MyFileDescriptorStruct>(arg, v2);
         else if (id == qMetaTypeId<QList<MyFileDescriptorStruct> >())
             return compare<QList<MyFileDescriptorStruct> >(arg, v2);
+
+        else if (id == qMetaTypeId<std::tuple<int>>())
+            return compare<std::tuple<int>>(arg, v2);
+        else if (id == qMetaTypeId<std::tuple<QString>>())
+            return compare<std::tuple<QString>>(arg, v2);
+        else if (id == qMetaTypeId<std::tuple<QVariantMap>>())
+            return compare<std::tuple<QVariantMap>>(arg, v2);
+        else if (id == qMetaTypeId<std::tuple<QPoint>>())
+            return compare<std::tuple<QPoint>>(arg, v2);
+        else if (id == qMetaTypeId<std::tuple<std::tuple<int>>>())
+            return compare<std::tuple<std::tuple<int>>>(arg, v2);
+        else if (id == qMetaTypeId<std::tuple<QList<int>>>())
+            return compare<std::tuple<QList<int>>>(arg, v2);
+        else if (id == qMetaTypeId<std::tuple<int, QString, QVariantMap>>())
+            return compare<std::tuple<int, QString, QVariantMap>>(arg, v2);
     }
 
     qWarning() << "Unexpected QVariant type" << v2.userType()

tests/auto/dbus/qdbusmarshall/tst_qdbusmarshall.cpp

@@ -549,6 +549,27 @@ void tst_QDBusMarshall::sendStructs_data()
     list << mvms;
     QTest::newRow("list-of-string-variantmap") << QVariant::fromValue(list) << "a(sa{sv})" << "[Argument: a(sa{sv}) {[Argument: (sa{sv}) \"Hello, World\", [Argument: a{sv} {\"bytearray\" = [Variant(QByteArray): {72, 101, 108, 108, 111, 44, 32, 119, 111, 114, 108, 100}], \"int\" = [Variant(int): 42], \"short\" = [Variant(short): -47], \"uint\" = [Variant(uint): 42]}]]}]";
 
+    QTest::newRow("std::tuple<int>")
+            << QVariant::fromValue(std::tuple<int>{ 1 }) << "(i)" << "[Argument: (i) 1]";
+    QTest::newRow("std::tuple<QString>") << QVariant::fromValue(std::tuple<QString>{ "foo" })
+                                         << "(s)" << "[Argument: (s) \"foo\"]";
+    QTest::newRow("std::tuple<QVariantMap>")
+            << QVariant::fromValue(std::tuple<QVariantMap>{ { { "foo", 1 } } }) << "(a{sv})"
+            << "[Argument: (a{sv}) [Argument: a{sv} {\"foo\" = [Variant(int): 1]}]]";
+    QTest::newRow("std::tuple<QPoint>") << QVariant::fromValue(std::tuple<QPoint>{ { 1, 2 } })
+                                        << "((ii))" << "[Argument: ((ii)) [Argument: (ii) 1, 2]]";
+    QTest::newRow("std::tuple<std::tuple<int>>")
+            << QVariant::fromValue(std::tuple<std::tuple<int>>{ 1 }) << "((i))"
+            << "[Argument: ((i)) [Argument: (i) 1]]";
+    QTest::newRow("std::tuple<QList<int>>")
+            << QVariant::fromValue(std::tuple<QList<int>>{ { 1, 2, 3 } }) << "(ai)"
+            << "[Argument: (ai) [Argument: ai {1, 2, 3}]]";
+    QTest::newRow("std::tuple<int, QString, QVariantMap>")
+            << QVariant::fromValue(
+                       std::tuple<int, QString, QVariantMap>{ 1, "foo", { { "bar", 2 } } })
+            << "(isa{sv})"
+            << "[Argument: (isa{sv}) 1, \"foo\", [Argument: a{sv} {\"bar\" = [Variant(int): 2]}]]";
+
     if (fileDescriptorPassing) {
         MyFileDescriptorStruct fds;
         fds.fd = QDBusUnixFileDescriptor(fileDescriptorForTest());