GUI: In Unix map Windows key as D-

Neovim now supports the D- modifer, which we already use in Mac OS X
for the Command key. This commit enables a similar behaviour for the
Windows key. Qt represents the Windows key as being the Meta key.

* Internally in input.cpp the key is named Cmd just like on Mac OS.
* Took the chance to remove the Key_Meta mapping since it was not being
  used.
* Added unit test to check if modifier keys are not being handled as
  regular keys.

src/gui/input.cpp

@@ -58,7 +58,7 @@ InputConv::InputConv() {
 QString InputConv::modPrefix(Qt::KeyboardModifiers mod)
 {
 	QString modprefix;
-#ifdef Q_OS_MAC
+#if defined(Q_OS_MAC) || defined(Q_OS_UNIX)
 	if ( mod & CmdModifier ) {
 		modprefix += "D-"; // like MacVim does
 	}

src/gui/input.h

@@ -28,14 +28,17 @@ class InputConv {
 	const Qt::KeyboardModifiers MetaModifier  = Qt::AltModifier;
 	const Qt::Key Key_Control = Qt::Key_Meta;
 	const Qt::Key Key_Cmd = Qt::Key_Control;
-	const Qt::Key Key_Meta = Qt::Key_Alt;
 #else
 	const Qt::KeyboardModifiers ControlModifier = Qt::ControlModifier;
+# ifdef Q_OS_UNIX
+	const Qt::KeyboardModifiers CmdModifier = Qt::MetaModifier;
+	const Qt::Key Key_Cmd = Qt::Key_Meta;;
+# else
 	const Qt::KeyboardModifiers CmdModifier = (Qt::KeyboardModifiers)0;
+	const Qt::Key Key_Cmd = (Qt::Key)0;
+# endif
 	const Qt::KeyboardModifiers MetaModifier  = Qt::MetaModifier;
 	const Qt::Key Key_Control = Qt::Key_Control;
-	const Qt::Key Key_Cmd = (Qt::Key)0;
-	const Qt::Key Key_Meta = Qt::Key_Meta;
 #endif
 	const Qt::KeyboardModifiers ShiftModifier = Qt::ShiftModifier;
 	const Qt::KeyboardModifiers AltModifier   = Qt::AltModifier;

test/tst_input.cpp

@@ -7,19 +7,29 @@ class TestInput: public QObject
 	Q_OBJECT
 private slots:
 	void specialKeys();
+	void modifiersAreNotKeys();
 private:
 	NeovimQt::InputConv input;
 };
 
+void TestInput::modifiersAreNotKeys()
+{
+	QCOMPARE(input.convertKey("", Qt::Key_Meta, Qt::MetaModifier),
+			QString());
+	QCOMPARE(input.convertKey("", Qt::Key_Control, Qt::ControlModifier),
+			QString());
+	QCOMPARE(input.convertKey("", Qt::Key_Alt, Qt::AltModifier),
+			QString());
+}
+
 void TestInput::specialKeys()
 {
 	foreach(int k, input.specialKeys.keys()) {
 		QCOMPARE(input.convertKey("", k, Qt::NoModifier),
 			QString("<%1>").arg(input.specialKeys.value(k)));
 
 #ifdef Q_OS_MAC
-		// On Mac Control is actually the Cmd key, which we
-		// don't support yet
+		// On Mac Control is actually the Cmd key
 		QCOMPARE(input.convertKey("", k, Qt::ControlModifier),
 			QString("<D-%1>").arg(input.specialKeys.value(k)));
 #else
@@ -30,10 +40,14 @@ void TestInput::specialKeys()
 		QCOMPARE(input.convertKey("", k, Qt::AltModifier),
 			QString("<A-%1>").arg(input.specialKeys.value(k)));
 
-#ifdef Q_OS_MAC
+#if defined(Q_OS_MAC)
 		QCOMPARE(input.convertKey("", k, Qt::MetaModifier),
 			// On Mac Meta is actually the Control key
 			QString("<C-%1>").arg(input.specialKeys.value(k)));
+#elif defined(Q_OS_UNIX)
+		QCOMPARE(input.convertKey("", k, Qt::MetaModifier),
+			// On UNIX Meta is the Windows key, treated as D-
+			QString("<D-%1>").arg(input.specialKeys.value(k)));
 #else
 		QCOMPARE(input.convertKey("", k, Qt::MetaModifier),
 			// Meta is not handled right now