qmltc: add singleton support

Add singleton support to qmltc.

Add the QML_SINGLETON annotation to the class, generate a static T*
create(QQmlEngine*, QJSEngine*) method for the engine and also add test
this new functionality.

Fixes: QTBUG-106828
Change-Id: I7b6b39ab0c8a427b3166562c3f04cf4a7eaa20e2
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

3 files changed, 29 insertions, 7 deletions

diff --git a/tools/qmltc/qmltccodewriter.cpp b/tools/qmltc/qmltccodewriter.cpp
index 7820af5ed8..68bd803b15 100644
--- a/tools/qmltc/qmltccodewriter.cpp
+++ b/tools/qmltc/qmltccodewriter.cpp
@@ -49,6 +49,7 @@ static QString getFunctionCategory(const QmltcMethod &method)
         category += u" Q_SLOTS"_s;
         break;
     case QQmlJSMetaMethod::Method:
+    case QQmlJSMetaMethod::StaticMethod:
         break;
     }
     return category;
@@ -287,6 +288,8 @@ void QmltcCodeWriter::write(QmltcOutputWrapper &code, const QmltcType &type)
             // TODO: ignoreInit must be eliminated
 
             QmltcCodeWriter::write(code, type.externalCtor);
+            if (type.staticCreate)
+                QmltcCodeWriter::write(code, *type.staticCreate);
         }
 
         // dtor
@@ -384,7 +387,10 @@ void QmltcCodeWriter::write(QmltcOutputWrapper &code, const QmltcMethod &method)
 {
     const auto [hSignature, cppSignature] = functionSignatures(method);
     // Note: augment return type with preambles in declaration
-    code.rawAppendToHeader(functionReturnType(method) + u" " + hSignature + u";");
+    code.rawAppendToHeader((method.type == QQmlJSMetaMethod::StaticMethod
+                                    ? u"static " + functionReturnType(method)
+                                    : functionReturnType(method))
+                           + u" " + hSignature + u";");
 
     // do not generate method implementation if it is a signal
     const auto methodType = method.type;
diff --git a/tools/qmltc/qmltccompiler.cpp b/tools/qmltc/qmltccompiler.cpp
index ddb10879db..f7d06d8e9a 100644
--- a/tools/qmltc/qmltccompiler.cpp
+++ b/tools/qmltc/qmltccompiler.cpp
@@ -165,11 +165,6 @@ void QmltcCompiler::compileType(
         QmltcType &current, const QQmlJSScope::ConstPtr &type,
         std::function<void(QmltcType &, const QQmlJSScope::ConstPtr &)> compileElements)
 {
-    if (type->isSingleton()) {
-        recordError(type->sourceLocation(), u"Singleton types are not supported"_s);
-        return;
-    }
-
     Q_ASSERT(!type->internalName().isEmpty());
     current.cppType = type->internalName();
     Q_ASSERT(!type->baseType()->internalName().isEmpty());
@@ -182,6 +177,7 @@ void QmltcCompiler::compileType(
     const bool documentRoot = (type == rootType);
     const bool inlineComponent = type->isInlineComponent();
     const bool isAnonymous = !documentRoot || type->internalName().at(0).isLower();
+    const bool isSingleton = type->isSingleton();
 
     QmltcCodeGenerator generator { m_url, m_visitor };
 
@@ -231,7 +227,7 @@ void QmltcCompiler::compileType(
 
     // add special member functions
     current.baselineCtor.access = QQmlJSMetaMethod::Protected;
-    if (documentRoot || inlineComponent) {
+    if (documentRoot || inlineComponent || isSingleton) {
         current.externalCtor.access = QQmlJSMetaMethod::Public;
     } else {
         current.externalCtor.access = QQmlJSMetaMethod::Protected;
@@ -318,6 +314,23 @@ void QmltcCompiler::compileType(
                         + u"(creator, engine, QQmlData::get(parent)->outerContext);";
     }
 
+    if (isSingleton) {
+        // see https://doc.qt.io/qt-6/qqmlengine.html#QML_SINGLETON for context
+        current.mocCode.append(u"QML_SINGLETON"_s);
+        auto &staticCreate = current.staticCreate.emplace();
+        staticCreate.comments
+                << u"Used by the engine for singleton creation."_s
+                << u"See also \\l {https://doc.qt.io/qt-6/qqmlengine.html#QML_SINGLETON}."_s;
+        staticCreate.type = QQmlJSMetaMethod::StaticMethod;
+        staticCreate.access = QQmlJSMetaMethod::Public;
+        staticCreate.name = u"create"_s;
+        staticCreate.returnType = u"%1 *"_s.arg(current.cppType);
+        QmltcVariable jsEngine(u"QJSEngine*"_s, u"jsEngine"_s);
+        staticCreate.parameterList = { engine, jsEngine };
+        staticCreate.body << u"Q_UNUSED(jsEngine);"_s
+                          << u"%1 *result = new %1(engine, nullptr);"_s.arg(current.cppType)
+                          << u"return result;"_s;
+    }
     auto postponedQmlContextSetup = generator.generate_initCode(current, type);
     generator.generate_endInitCode(current, type);
     generator.generate_setComplexBindingsCode(current, type);
diff --git a/tools/qmltc/qmltcoutputir.h b/tools/qmltc/qmltcoutputir.h
index 46f8e46ee8..8884ddc3a3 100644
--- a/tools/qmltc/qmltcoutputir.h
+++ b/tools/qmltc/qmltcoutputir.h
@@ -128,6 +128,9 @@ struct QmltcType
 
     // TODO: only needed for binding callables - should not be needed, generally
     bool ignoreInit = false; // specifies whether init and externalCtor should be ignored
+
+    // needed for singletons
+    std::optional<QmltcMethod> staticCreate{};
 };
 
 // Represents whole QML program, compiled to C++