Implement QMetaType::canConvert() and use it in QVariant

Use the fact that we return the conversion function as a lambda
to find out reliably whether a conversion between two types
can be done.

This requires some minor adjustments to our tests:

* Nothing can convert to an unknown type and vice versa
* Adjust results to the fact that we don't convert from char
  to QString anymore (where the old method was incorrect)
* QStringList->QString requires some adjustments, as we only
  convert if the string list has exactly one element. For now
  we return true in canConvert(), but the conversion behavior
  in this case is something we should rethink, as it is very
  surprising.

Change-Id: I3f5f87ee9cb99d690f5a7d13b13d6a6313d8038e
Reviewed-by: Maurice Kalinowski <maurice.kalinowski@qt.io>

1 files changed, 8 insertions, 8 deletions

diff --git a/tests/auto/corelib/kernel/qvariant/tst_qvariant.cpp b/tests/auto/corelib/kernel/qvariant/tst_qvariant.cpp
index a722e53f48..d4af02baf1 100644
--- a/tests/auto/corelib/kernel/qvariant/tst_qvariant.cpp
+++ b/tests/auto/corelib/kernel/qvariant/tst_qvariant.cpp
@@ -477,7 +477,7 @@ void tst_QVariant::canConvert_data()
         << var << N << N << Y << N << Y << N << N << N << N << Y << N << N << Y << N << Y << N << Y << N << N << N << N << N << N << N << N << N << Y << N << N << Y << Y;
     var = QVariant();
     QTest::newRow("Invalid")
-        << var << N << N << N << N << N << N << N << N << N << N << N << N << N << Y << N << N << N << N << N << N << N << N << N << N << N << N << N << N << N << N << N;
+        << var << N << N << N << N << N << N << N << N << N << N << N << N << N << N << N << N << N << N << N << N << N << N << N << N << N << N << N << N << N << N << N;
     var = QVariant(QList<QVariant>());
     QTest::newRow("List")
         << var << N << N << N << N << N << N << N << N << N << N << N << N << N << N << N << Y << N << N << N << N << N << N << N << N << N << N << N << Y << N << N << N;
@@ -520,12 +520,12 @@ void tst_QVariant::canConvert_data()
     var = QVariant::fromValue<signed char>(-1);
     QTest::newRow("SChar")
         << var << N << N << Y << N << Y << N << N << N << N << Y << N << N << Y << N << N << N << Y << N << N << N << N << N << N << N << N << N << Y << N << N << Y << Y;
-    var = QVariant((short)-3);
+    var = QVariant::fromValue((short)-3);
     QTest::newRow("Short")
-        << var << N << N << Y << N << Y << N << N << N << N << Y << N << N << Y << N << Y << N << Y << N << N << N << N << N << N << N << N << N << Y << N << N << Y << Y;
-    var = QVariant((ushort)7);
+        << var << N << N << Y << N << Y << N << N << N << N << Y << N << N << Y << N << N << N << Y << N << N << N << N << N << N << N << N << N << Y << N << N << Y << Y;
+    var = QVariant::fromValue((ushort)7);
     QTest::newRow("UShort")
-        << var << N << N << Y << N << Y << N << N << N << N << Y << N << N << Y << N << Y << N << Y << N << N << N << N << N << N << N << N << N << Y << N << N << Y << Y;
+        << var << N << N << Y << N << Y << N << N << N << N << Y << N << N << Y << N << N << N << Y << N << N << N << N << N << N << N << N << N << Y << N << N << Y << Y;
     var = QVariant::fromValue<QJsonValue>(QJsonValue(QStringLiteral("hello")));
     QTest::newRow("JsonValue")
         << var << N << N << Y << N << N << N << N << N << N << Y << N << N << Y << N << N << Y << Y << Y << N << N << N << N << N << N << N << N << Y << N << N << Y << Y;
@@ -2705,17 +2705,17 @@ void tst_QVariant::canConvertQStringList_data() const
     QTest::addColumn<QStringList>("input");
     QTest::addColumn<QString>("result");
 
-    QTest::newRow("An empty list") << false << QStringList() << QString();
+    QTest::newRow("An empty list") << true << QStringList() << QString();
     QTest::newRow("A single item") << true << QStringList(QLatin1String("foo")) << QString::fromLatin1("foo");
     QTest::newRow("A single, but empty item") << true << QStringList(QString()) << QString();
 
     QStringList l;
     l << "a" << "b";
 
-    QTest::newRow("Two items") << false << l << QString();
+    QTest::newRow("Two items") << true << l << QString();
 
     l << "c";
-    QTest::newRow("Three items") << false << l << QString();
+    QTest::newRow("Three items") << true << l << QString();
 }
 
 template<typename T> void convertMetaType()