QmlJSCheck: Do not allow object in when condition

This is syntactically correct and can be hard to spot, but
is not valid QtQuick.

Task-number: QDS-13452
Change-Id: I010e44e33147c97edbd992c3452ba1c086fb42cb
Reviewed-by: Marco Bubke <marco.bubke@qt.io>
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

src/libs/qmljs/qmljscheck.cpp

@@ -953,6 +953,13 @@ bool Check::visit(UiObjectBinding *ast)
         //addMessage(ErrBehavioursNotSupportedInQmlUi, locationFromRange(ast->firstSourceLocation(), ast->lastSourceLocation()));
     }
 
+    if (!m_typeStack.isEmpty() && m_typeStack.last() == "State"
+        && toString(ast->qualifiedId) == "when") {
+        addMessage(
+            ErrWhenConditionCannotBeObject,
+            locationFromRange(ast->firstSourceLocation(), ast->lastSourceLocation()));
+    }
+
     visitQmlObject(ast, ast->qualifiedTypeNameId, ast->initializer);
     return false;
 }

src/libs/qmljs/qmljsstaticanalysismessage.cpp

@@ -238,6 +238,7 @@ StaticAnalysisMessages::StaticAnalysisMessages()
            Tr::tr("Do not reference the root item as alias."));
     newMsg(WarnAliasReferRootHierarchy, Warning,
            Tr::tr("Avoid referencing the root item in a hierarchy."));
+    newMsg(ErrWhenConditionCannotBeObject, Error, Tr::tr("When condtion cannot contain an object."));
 }
 
 } // anonymous namespace

src/libs/qmljs/qmljsstaticanalysismessage.h

@@ -113,7 +113,8 @@ enum Type {
     WarnComponentRequiresChildren = 327,
     WarnDuplicateImport = 400,
     ErrAliasReferRoot = 401,
-    WarnAliasReferRootHierarchy = 402
+    WarnAliasReferRootHierarchy = 402,
+    ErrWhenConditionCannotBeObject = 403,
 };
 
 class QMLJS_EXPORT PrototypeMessageData {