QmlJS: Add error message for Component with multiple children

Component is only allowed to have a single child element, that will
be the root element of the component.

If there is no child at all we create a warning. Having no child is
temporarily required.

Change-Id: I5c0d9d9cdf1be106b20ed4f1134a973d58126498
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Miikka Heikkinen <miikka.heikkinen@qt.io>
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>

src/libs/qmljs/qmljscheck.cpp

@@ -794,8 +794,10 @@ bool Check::visit(UiObjectInitializer *)
     UiQualifiedId *qualifiedTypeId = qualifiedTypeNameId(parent());
     if (qualifiedTypeId) {
         typeName = qualifiedTypeId->name.toString();
-        if (typeName == "Component")
+        if (typeName == "Component") {
             m_idStack.push(StringSet());
+            _componentChildCount = 0;
+        }
     }
 
     m_typeStack.push(typeName);
@@ -806,10 +808,23 @@ bool Check::visit(UiObjectInitializer *)
     return true;
 }
 
-void Check::endVisit(UiObjectInitializer *)
+void Check::endVisit(UiObjectInitializer *uiObjectInitializer)
 {
     m_propertyStack.pop();
-    m_typeStack.pop();
+
+    const QString type = m_typeStack.pop();
+
+    if (type == "Component" && _componentChildCount == 0) {
+        SourceLocation loc;
+        UiObjectDefinition *objectDefinition = cast<UiObjectDefinition *>(parent());
+        if (objectDefinition)
+            loc = objectDefinition->qualifiedTypeNameId->identifierToken;
+        UiObjectBinding *objectBinding = cast<UiObjectBinding *>(parent());
+        if (objectBinding)
+            loc = objectBinding->qualifiedTypeNameId->identifierToken;
+        addMessage(WarnComponentRequiresChildren, loc);
+    }
+
     UiObjectDefinition *objectDefinition = cast<UiObjectDefinition *>(parent());
     if (objectDefinition && objectDefinition->qualifiedTypeNameId->name == QLatin1String("Component"))
         m_idStack.pop();
@@ -962,6 +977,12 @@ void Check::visitQmlObject(Node *ast, UiQualifiedId *typeId,
         addMessage(ErrUnsupportedRootTypeInQmlUi,
                    locationFromRange(ast->firstSourceLocation(), ast->lastSourceLocation()), typeName);
 
+    if (!m_typeStack.isEmpty() && m_typeStack.last() == "Component") {
+        _componentChildCount++;
+        if (_componentChildCount > 1)
+            addMessage(ErrToManyComponentChildren, typeErrorLocation);
+    }
+
     bool typeError = false;
     if (_importsOk) {
         const ObjectValue *prototype = _context->lookupType(_doc.data(), typeId);

src/libs/qmljs/qmljscheck.h

@@ -158,6 +158,7 @@ private:
 
     bool _importsOk;
     bool _inStatementBinding;
+    int _componentChildCount = 0;
     const Imports *_imports;
     TranslationFunction lastTransLationfunction = noTranslationfunction;
 };

src/libs/qmljs/qmljsstaticanalysismessage.cpp

@@ -251,6 +251,10 @@ StaticAnalysisMessages::StaticAnalysisMessages()
             tr("Type cannot be instantiated recursively (%1)."), 1);
     newMsg(WarnLogicalValueDoesNotDependOnValues, Warning,
            tr("Logical value does not depend on actual values"));
+    newMsg(ErrToManyComponentChildren, Error,
+           tr("Components are only allowed to have a single child element."));
+    newMsg(WarnComponentRequiresChildren, Warning,
+           tr("Components require a child element."));
 }
 
 } // anonymous namespace

src/libs/qmljs/qmljsstaticanalysismessage.h

@@ -132,6 +132,8 @@ enum Type {
     ErrInvalidArrayValueLength = 323,
     ErrHitMaximumRecursion = 324,
     WarnLogicalValueDoesNotDependOnValues = 325,
+    ErrToManyComponentChildren = 326,
+    WarnComponentRequiresChildren = 327,
     WarnDuplicateImport = 400
 };