Introduce Q_PROPERTY attribute REQUIRED

This is meant to correspond to required properties in QML.

Change-Id: I2645981e13f7423bc86b48370c165b3cfe2aaa62
Task-number: QTBUG-81561
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

src/corelib/doc/snippets/code/doc_src_properties.cpp

@@ -61,6 +61,7 @@ Q_PROPERTY(type name
            [USER bool]
            [CONSTANT]
            [FINAL])
+           [REQUIRED]
 //! [0]
 
 

src/corelib/doc/src/objectmodel/properties.qdoc

@@ -144,6 +144,12 @@
     optimizations in some cases, but is not enforced by moc.  Care must be taken
     never to override a \c FINAL property.
 
+    \li The presence of the \c REQUIRED attribute indicates that the property
+    should be set by a user of the class. This is not enforced by moc, and is
+    mostly useful for classes exposed to QML. In QML, classes with REQUIRED
+    properties cannot be instantiated unless all REQUIRED properties have
+    been set.
+
     \endlist
 
     The \c READ, \c WRITE, and \c RESET functions can be inherited.

src/corelib/kernel/qmetaobject.cpp

@@ -3572,6 +3572,21 @@ bool QMetaProperty::isFinal() const
     return flags & Final;
 }
 
+/*!
+  \since 5.15
+  Returns \c true if the property is required; otherwise returns \c false.
+
+  A property is final if the \c{Q_PROPERTY()}'s \c REQUIRED attribute
+  is set.
+*/
+bool QMetaProperty::isRequired() const
+{
+    if (!mobj)
+        return false;
+    int flags = mobj->d.data[handle + 2];
+    return flags & Required;
+}
+
 /*!
     \obsolete
 

src/corelib/kernel/qmetaobject.h

@@ -266,6 +266,7 @@ public:
     bool isUser(const QObject *obj = nullptr) const;
     bool isConstant() const;
     bool isFinal() const;
+    bool isRequired() const;
 
     bool isFlagType() const;
     bool isEnumType() const;

src/corelib/kernel/qmetaobject_p.h

@@ -85,7 +85,8 @@ enum PropertyFlags  {
     User = 0x00100000,
     ResolveUser = 0x00200000,
     Notify = 0x00400000,
-    Revisioned = 0x00800000
+    Revisioned = 0x00800000,
+    Required = 0x01000000,
 };
 
 enum MethodFlags  {

src/tools/moc/generator.cpp

@@ -864,6 +864,8 @@ void Generator::generateProperties()
             flags |= Constant;
         if (p.final)
             flags |= Final;
+        if (p.required)
+            flags |= Required;
 
         fprintf(out, "    %4d, ", stridx(p.name));
         generateTypeInfo(p.type);

src/tools/moc/moc.cpp

@@ -1238,6 +1238,9 @@ void Moc::createPropertyDef(PropertyDef &propDef)
         } else if(l[0] == 'F' && l == "FINAL") {
             propDef.final = true;
             continue;
+        } else if (l[0] == 'R' && l == "REQUIRED") {
+            propDef.required = true;
+            continue;
         }
 
         QByteArray v, v2;
@@ -1960,6 +1963,7 @@ QJsonObject PropertyDef::toJson() const
 
     prop[QLatin1String("constant")] = constant;
     prop[QLatin1String("final")] = final;
+    prop[QLatin1String("required")] = required;
 
     if (revision > 0)
         prop[QLatin1String("revision")] = revision;

src/tools/moc/moc.h

@@ -137,6 +137,7 @@ struct PropertyDef
     int revision = 0;
     bool constant = false;
     bool final = false;
+    bool required = false;
 
     QJsonObject toJson() const;
 };

tests/auto/tools/moc/allmocs_baseline_in.json

@@ -275,6 +275,7 @@
                         "final": false,
                         "name": "flags",
                         "read": "flags",
+                        "required": false,
                         "scriptable": true,
                         "stored": true,
                         "type": "Flags",
@@ -299,6 +300,7 @@
                         "final": false,
                         "name": "flags",
                         "read": "flags",
+                        "required": false,
                         "scriptable": true,
                         "stored": true,
                         "type": "Foo::Bar::Flags",
@@ -311,6 +313,7 @@
                         "final": false,
                         "name": "flagsList",
                         "read": "flagsList",
+                        "required": false,
                         "scriptable": true,
                         "stored": true,
                         "type": "QList<Foo::Bar::Flags>",
@@ -1988,6 +1991,7 @@
                         "final": false,
                         "name": "blah",
                         "read": "blah",
+                        "required": false,
                         "scriptable": true,
                         "stored": true,
                         "type": "A::SomeEnum",
@@ -2088,6 +2092,7 @@
                         "final": false,
                         "name": "blah",
                         "read": "blah",
+                        "required": false,
                         "scriptable": true,
                         "stored": true,
                         "type": "A::SomeEnum",
@@ -2257,6 +2262,7 @@
                         "final": false,
                         "name": "gadgetPoperty",
                         "read": "gadgetPoperty",
+                        "required": false,
                         "scriptable": true,
                         "stored": true,
                         "type": "Gadget::SomeEnum",
@@ -2268,6 +2274,7 @@
                         "final": false,
                         "name": "objectPoperty",
                         "read": "objectPoperty",
+                        "required": false,
                         "scriptable": true,
                         "stored": true,
                         "type": "Object::SomeEnum",
@@ -2291,6 +2298,7 @@
                         "final": false,
                         "name": "nestedGadgetPoperty",
                         "read": "nestedGadgetPoperty",
+                        "required": false,
                         "scriptable": true,
                         "stored": true,
                         "type": "Nested::Gadget::SomeEnum",
@@ -2314,6 +2322,7 @@
                         "final": false,
                         "name": "nestedObjectPoperty",
                         "read": "nestedObjectPoperty",
+                        "required": false,
                         "scriptable": true,
                         "stored": true,
                         "type": "Nested::Object::SomeEnum",
@@ -2442,6 +2451,7 @@
                         "final": false,
                         "name": "gadgetPoperty",
                         "read": "gadgetPoperty",
+                        "required": false,
                         "scriptable": true,
                         "stored": true,
                         "type": "Gadget::SomeEnum",
@@ -2453,6 +2463,7 @@
                         "final": false,
                         "name": "objectPoperty",
                         "read": "objectPoperty",
+                        "required": false,
                         "scriptable": true,
                         "stored": true,
                         "type": "Object::SomeEnum",
@@ -2476,6 +2487,7 @@
                         "final": false,
                         "name": "nestedGadgetPoperty",
                         "read": "nestedGadgetPoperty",
+                        "required": false,
                         "scriptable": true,
                         "stored": true,
                         "type": "Nested::Gadget::SomeEnum",
@@ -2499,6 +2511,7 @@
                         "final": false,
                         "name": "nestedObjectPoperty",
                         "read": "nestedObjectPoperty",
+                        "required": false,
                         "scriptable": true,
                         "stored": true,
                         "type": "Nested::Object::SomeEnum",

tests/auto/tools/moc/tst_moc.cpp

@@ -719,6 +719,7 @@ private slots:
     void cxx17Namespaces();
     void cxxAttributes();
     void mocJsonOutput();
+    void requiredProperties();
 
 signals:
     void sigWithUnsignedArg(unsigned foo);
@@ -4025,6 +4026,29 @@ void tst_Moc::mocJsonOutput()
     QVERIFY2(actualOutput == expectedOutput, showPotentialDiff(actualOutput, expectedOutput).constData());
 }
 
+class RequiredTest :public QObject
+{
+    Q_OBJECT
+
+    Q_PROPERTY(int required MEMBER m_required REQUIRED)
+    Q_PROPERTY(int notRequired MEMBER m_notRequired)
+
+private:
+    int m_required;
+    int m_notRequired;
+};
+
+void tst_Moc::requiredProperties()
+{
+    QMetaObject mo = RequiredTest::staticMetaObject;
+    QMetaProperty required = mo.property(mo.indexOfProperty("required"));
+    QVERIFY(required.isValid());
+    QVERIFY(required.isRequired());
+    QMetaProperty notRequired = mo.property(mo.indexOfProperty("notRequired"));
+    QVERIFY(notRequired.isValid());
+    QVERIFY(!notRequired.isRequired());
+}
+
 QTEST_MAIN(tst_Moc)
 
 // the generated code must compile with QT_NO_KEYWORDS