Moc: fix generated code for nested enum class corner case

Fixes an issue with generated code where the name of an enclosing
namespace is identical to an enum class type, when Q_ENUM_NS is used.

Consider:
namespace a {
    Q_NAMESPACE
    namespace b {
        enum class b { Key, Key2 };
        Q_ENUM_NS(b);
    }
}

moc generated code such as:
Q_CONSTINIT const QMetaObject a::b::staticMetaObject = { {
    ...
    qt_incomplete_metaTypeArray<qt_meta_stringdata_CLASSaSCOPEbENDCLASS_t,
        // enum 'TestEnum'
        QtPrivate::TypeAndForceComplete<b::b, std::true_type>,
        // Q_OBJECT / Q_GADGET
        QtPrivate::TypeAndForceComplete<void, std::true_type>
    >,
    nullptr
} };

which confused the compiler:
error: ‘b’ is not a member of ‘a::b::b
   83 |         QtPrivate::TypeAndForceComplete<b::b, std::true_type>,

Fixes: QTBUG-112996
Pick-to: 6.6
Change-Id: I37aee83c32efe96cc9d6c2bd0bdb9ba80bb7b8a7
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

3 files changed, 21 insertions, 2 deletions

diff --git a/src/tools/moc/generator.cpp b/src/tools/moc/generator.cpp
index f3a53dfccd..b083ed63b7 100644
--- a/src/tools/moc/generator.cpp
+++ b/src/tools/moc/generator.cpp
@@ -525,8 +525,7 @@ void Generator::generateCode()
     // metatypes for enums
     for (const EnumDef &e : std::as_const(cdef->enumList)) {
         fprintf(out, "%s\n        // enum '%s'\n        %s",
-                comma, e.name.constData(),
-                stringForType(cdef->classname % "::" % e.name, true).constData());
+                comma, e.name.constData(), stringForType(e.qualifiedType(cdef), true).constData());
         comma = ",";
     }
 
diff --git a/src/tools/moc/moc.cpp b/src/tools/moc/moc.cpp
index 058df18f42..1d1948525c 100644
--- a/src/tools/moc/moc.cpp
+++ b/src/tools/moc/moc.cpp
@@ -2187,4 +2187,23 @@ QJsonObject EnumDef::toJson(const ClassDef &cdef) const
     return def;
 }
 
+QByteArray EnumDef::qualifiedType(const ClassDef *cdef) const
+{
+    if (name == cdef->classname) {
+        // The name of the enclosing namespace is the same as the enum class name
+        if (cdef->qualified.contains("::")) {
+            // QTBUG-112996, fully qualify by using cdef->qualified to disambiguate enum
+            // class name and enclosing namespace, e.g.:
+            // namespace A { namespace B { Q_NAMESPACE; enum class B { }; Q_ENUM_NS(B) } }
+            return cdef->qualified % "::" % name;
+        } else {
+            // Just "B"; otherwise the compiler complains about the type "B::B" inside
+            // "B::staticMetaObject" in the generated code; e.g.:
+            // namespace B { Q_NAMESPACE; enum class B { }; Q_ENUM_NS(B) }
+            return name;
+        }
+    }
+    return cdef->classname % "::" % name;
+}
+
 QT_END_NAMESPACE
diff --git a/src/tools/moc/moc.h b/src/tools/moc/moc.h
index 04f1c835ce..a3ddb835b5 100644
--- a/src/tools/moc/moc.h
+++ b/src/tools/moc/moc.h
@@ -48,6 +48,7 @@ struct EnumDef
     bool isEnumClass; // c++11 enum class
     EnumDef() : isEnumClass(false) {}
     QJsonObject toJson(const ClassDef &cdef) const;
+    QByteArray qualifiedType(const ClassDef *cdef) const;
 };
 Q_DECLARE_TYPEINFO(EnumDef, Q_RELOCATABLE_TYPE);