qmltc: Remove broken alias optimization

Remove the recursive alias resolution mechanism. It tried to resolve
aliases recursively but only knew the id's of the current component.
This means that an alias pointing to a property defined in another
component (e.g. a different qml file) was resolved using the
id-to-scope map of the component containing the alias property.
This leads to unresolved aliases at best and endless loops when the
aliased property was itself an alias pointing to some property also
existing in the original component (see
QmltcTests/ComponentWithAlias{1..3}.qml for an example).

Also added the reproducer in the qmltc tests.

Fixes: QTBUG-107533
Fixes: QTBUG-107534
Change-Id: Idbf0cff3e45213bc7fbb4a98a9393c6754b00046
Pick-to: 6.4
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

8 files changed, 97 insertions, 8 deletions

diff --git a/src/qmlcompiler/qqmljsutils.cpp b/src/qmlcompiler/qqmljsutils.cpp
index 229e8f29ad..0ced8254b5 100644
--- a/src/qmlcompiler/qqmljsutils.cpp
+++ b/src/qmlcompiler/qqmljsutils.cpp
@@ -25,17 +25,23 @@ resolveAlias(ScopeForId scopeForId, const QQmlJSMetaProperty &property,
     QQmlJSUtils::ResolvedAlias result {};
     result.owner = owner;
 
-    for (QQmlJSMetaProperty nextProperty = property; nextProperty.isAlias();) {
-
-        // this is a special (seemingly useless) section which is necessary when
-        // we have an alias pointing to an alias. this way we avoid a check
-        // whether a property is an alias at the very end of the loop body
+    // TODO: one could optimize the generated alias code for aliases pointing to aliases
+    //  e.g., if idA.myAlias -> idB.myAlias2 -> idC.myProp, then one could directly generate
+    //  idA.myProp as pointing to idC.myProp.
+    //  This gets complicated when idB.myAlias is in a different Component than where the
+    //  idA.myAlias is defined: scopeForId currently only contains the ids of the current
+    //  component and alias resolution on the ids of a different component fails then.
+    if (QQmlJSMetaProperty nextProperty = property; nextProperty.isAlias()) {
         QQmlJSScope::ConstPtr resultOwner = result.owner;
         result = QQmlJSUtils::ResolvedAlias {};
 
         visitor.reset();
 
         auto aliasExprBits = nextProperty.aliasExpression().split(u'.');
+        // do not crash on invalid aliasexprbits when accessing aliasExprBits[0]
+        if (aliasExprBits.size() < 1)
+            return {};
+
         // resolve id first:
         resultOwner = scopeForId(aliasExprBits[0], resultOwner);
         if (!resultOwner)
@@ -46,8 +52,6 @@ resolveAlias(ScopeForId scopeForId, const QQmlJSMetaProperty &property,
         aliasExprBits.removeFirst(); // Note: for simplicity, remove the <id>
         result.owner = resultOwner;
         result.kind = QQmlJSUtils::AliasTarget_Object;
-        // reset the property to avoid endless loop when aliasExprBits is empty
-        nextProperty = QQmlJSMetaProperty {};
 
         for (const QString &bit : std::as_const(aliasExprBits)) {
             nextProperty = resultOwner->property(bit);
diff --git a/tests/auto/qml/qmltc/QmltcTests/CMakeLists.txt b/tests/auto/qml/qmltc/QmltcTests/CMakeLists.txt
index 7712dcf992..36e4d1413b 100644
--- a/tests/auto/qml/qmltc/QmltcTests/CMakeLists.txt
+++ b/tests/auto/qml/qmltc/QmltcTests/CMakeLists.txt
@@ -101,6 +101,7 @@ set(qml_sources
     appendToQQmlListProperty.qml
     inlineComponents.qml
     repeaterCrash.qml
+    aliases.qml
 
     # support types:
     DefaultPropertySingleChild.qml
@@ -110,6 +111,9 @@ set(qml_sources
     LocalWithOnCompleted.qml
     LocallyImported_context.qml
 #   SingletonThing.qml
+    ComponentWithAlias1.qml
+    ComponentWithAlias2.qml
+    ComponentWithAlias3.qml
 
     badFile.qml
 )
diff --git a/tests/auto/qml/qmltc/QmltcTests/ComponentWithAlias1.qml b/tests/auto/qml/qmltc/QmltcTests/ComponentWithAlias1.qml
new file mode 100644
index 0000000000..210cf1e159
--- /dev/null
+++ b/tests/auto/qml/qmltc/QmltcTests/ComponentWithAlias1.qml
@@ -0,0 +1,8 @@
+import QtQuick
+
+Item {
+    property alias setMe: firstComponent.setMe
+    ComponentWithAlias2 {
+        id: firstComponent
+    }
+}
diff --git a/tests/auto/qml/qmltc/QmltcTests/ComponentWithAlias2.qml b/tests/auto/qml/qmltc/QmltcTests/ComponentWithAlias2.qml
new file mode 100644
index 0000000000..818f3a464e
--- /dev/null
+++ b/tests/auto/qml/qmltc/QmltcTests/ComponentWithAlias2.qml
@@ -0,0 +1,8 @@
+import QtQuick
+
+Item {
+    property alias setMe: firstComponent.setMe
+    ComponentWithAlias3 {
+        id: firstComponent
+    }
+}
diff --git a/tests/auto/qml/qmltc/QmltcTests/ComponentWithAlias3.qml b/tests/auto/qml/qmltc/QmltcTests/ComponentWithAlias3.qml
new file mode 100644
index 0000000000..87b917ad19
--- /dev/null
+++ b/tests/auto/qml/qmltc/QmltcTests/ComponentWithAlias3.qml
@@ -0,0 +1,5 @@
+import QtQuick
+
+Item {
+    property string setMe: "Set me!"
+}
diff --git a/tests/auto/qml/qmltc/QmltcTests/aliases.qml b/tests/auto/qml/qmltc/QmltcTests/aliases.qml
new file mode 100644
index 0000000000..9f13f7b17a
--- /dev/null
+++ b/tests/auto/qml/qmltc/QmltcTests/aliases.qml
@@ -0,0 +1,29 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
+
+import QtQuick
+
+Item {
+    property alias aliasToAlias: subItem.aliasToAlias
+    Item {
+        id: subItem
+        property alias aliasToAlias: subsubItem.aliasToAlias
+
+        Item {
+            id: subsubItem
+            property alias aliasToAlias: subsubsubItem.value
+
+                Item {
+                id: subsubsubItem
+                property string value: "Hello World!"
+            }
+        }
+    }
+
+    property alias aliasToOtherFile: inOtherFile.setMe
+
+    ComponentWithAlias1 {
+        id: inOtherFile
+    }
+}
+
diff --git a/tests/auto/qml/qmltc/tst_qmltc.cpp b/tests/auto/qml/qmltc/tst_qmltc.cpp
index 26265fcb46..2c5a164989 100644
--- a/tests/auto/qml/qmltc/tst_qmltc.cpp
+++ b/tests/auto/qml/qmltc/tst_qmltc.cpp
@@ -76,7 +76,7 @@
 #include "appendtoqqmllistproperty.h"
 #include "inlinecomponents.h"
 #include "repeatercrash.h"
-
+#include "aliases.h"
 #include "testprivateproperty.h"
 
 // Qt:
@@ -2930,4 +2930,34 @@ void tst_qmltc::inlineComponents()
     }
 }
 
+void tst_qmltc::aliases()
+{
+    QQmlEngine e;
+    PREPEND_NAMESPACE(aliases) fromQmltc(&e);
+
+    QQmlComponent component(&e);
+    component.loadUrl(QUrl("qrc:/qt/qml/QmltcTests/aliases.qml"));
+    QVERIFY(!component.isError());
+    QScopedPointer<QObject> fromComponent(component.create());
+    const QString testString = u"myTestString"_s;
+
+    QCOMPARE(fromQmltc.aliasToAlias(), u"Hello World!"_s);
+    QCOMPARE(fromComponent->property("aliasToAlias"), u"Hello World!"_s);
+
+    fromQmltc.setAliasToAlias(testString);
+    QVERIFY(fromComponent->setProperty("aliasToAlias", testString));
+
+    QCOMPARE(fromQmltc.aliasToAlias(), testString);
+    QCOMPARE(fromComponent->property("aliasToAlias"), testString);
+
+    QCOMPARE(fromQmltc.aliasToOtherFile(), u"Set me!"_s);
+    QCOMPARE(fromComponent->property("aliasToOtherFile"), u"Set me!"_s);
+
+    fromQmltc.setAliasToOtherFile(testString);
+    QVERIFY(fromComponent->setProperty("aliasToOtherFile", testString));
+
+    QCOMPARE(fromQmltc.aliasToOtherFile(), testString);
+    QCOMPARE(fromComponent->property("aliasToOtherFile"), testString);
+}
+
 QTEST_MAIN(tst_qmltc)
diff --git a/tests/auto/qml/qmltc/tst_qmltc.h b/tests/auto/qml/qmltc/tst_qmltc.h
index 0eea63b0f2..eaa4bed27a 100644
--- a/tests/auto/qml/qmltc/tst_qmltc.h
+++ b/tests/auto/qml/qmltc/tst_qmltc.h
@@ -88,4 +88,5 @@ private slots:
     void generalizedGroupedProperty();
     void appendToQQmlListProperty();
     void inlineComponents();
+    void aliases();
 };