QML: Special case null as binding type

This gives us the opportunity to map the JavaScript null to QVariant's
concept of isNull().

[ChangeLog][QML] Assigning JavaScript null to incompatibly typed
properties generates a compile error now, rather than a runtime error.

Fixes: QTBUG-72098
Change-Id: I72fd1c30d84128c774230eaaea10455b2a0e064c
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

4 files changed, 10 insertions, 0 deletions

diff --git a/src/qml/compiler/qqmlirbuilder.cpp b/src/qml/compiler/qqmlirbuilder.cpp
index 84fd66b114..be5e0480b8 100644
--- a/src/qml/compiler/qqmlirbuilder.cpp
+++ b/src/qml/compiler/qqmlirbuilder.cpp
@@ -1083,6 +1083,9 @@ void IRBuilder::setBindingValue(QV4::CompiledData::Binding *binding, QQmlJS::AST
                 binding->type = QV4::CompiledData::Binding::Type_Number;
                 binding->value.constantValueIndex = jsGenerator->registerConstant(QV4::Encode(-lit->value));
             }
+        } else if (QQmlJS::AST::cast<QQmlJS::AST::NullExpression *>(expr)) {
+            binding->type = QV4::CompiledData::Binding::Type_Null;
+            binding->value.nullMarker = 0;
         }
     }
 
diff --git a/src/qml/compiler/qqmlpropertyvalidator.cpp b/src/qml/compiler/qqmlpropertyvalidator.cpp
index 4cb922ca8d..3b97e364e1 100644
--- a/src/qml/compiler/qqmlpropertyvalidator.cpp
+++ b/src/qml/compiler/qqmlpropertyvalidator.cpp
@@ -575,6 +575,9 @@ QQmlCompileError QQmlPropertyValidator::validateLiteralBinding(QQmlPropertyCache
             break;
         } else if (property->propType() == qMetaTypeId<QQmlScriptString>()) {
             break;
+        } else if (property->isQObject()
+                   && binding->type == QV4::CompiledData::Binding::Type_Null) {
+            break;
         }
 
         // otherwise, try a custom type assignment
diff --git a/src/qml/compiler/qv4compileddata.cpp b/src/qml/compiler/qv4compileddata.cpp
index e68a563a45..9379160a65 100644
--- a/src/qml/compiler/qv4compileddata.cpp
+++ b/src/qml/compiler/qv4compileddata.cpp
@@ -745,6 +745,8 @@ QString Binding::valueAsString(const CompilationUnit *unit) const
     case Type_Script:
     case Type_String:
         return unit->stringAt(stringIndex);
+    case Type_Null:
+        return QStringLiteral("null");
     case Type_Boolean:
         return value.b ? QStringLiteral("true") : QStringLiteral("false");
     case Type_Number:
diff --git a/src/qml/compiler/qv4compileddata_p.h b/src/qml/compiler/qv4compileddata_p.h
index 7c26b0b67d..5732855cc9 100644
--- a/src/qml/compiler/qv4compileddata_p.h
+++ b/src/qml/compiler/qv4compileddata_p.h
@@ -440,6 +440,7 @@ struct Q_QML_PRIVATE_EXPORT Binding
         Type_Boolean,
         Type_Number,
         Type_String,
+        Type_Null,
         Type_Translation,
         Type_TranslationById,
         Type_Script,
@@ -471,6 +472,7 @@ struct Q_QML_PRIVATE_EXPORT Binding
         quint32_le compiledScriptIndex; // used when Type_Script
         quint32_le objectIndex;
         quint32_le translationDataIndex; // used when Type_Translation
+        quint32 nullMarker;
     } value;
     quint32_le stringIndex; // Set for Type_String and Type_Script (the latter because of script strings)