From 6dfbbc2a5435d2e9542e9cf2eb039147db0ff29b Mon Sep 17 00:00:00 2001
From: Fabian Kosmale <fabian.kosmale@qt.io>
Date: Mon, 6 Jan 2020 17:08:41 +0100
Subject: QV4: Support printing arrays with circular references

Fixes: QTBUG-81105
Change-Id: Iaf0597cea3a5572f020c5f87a843774f33cc01fd
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
---
 src/qml/qml/v8/qqmlbuiltinfunctions.cpp    | 13 +++++++++----
 tests/auto/qml/qjsengine/tst_qjsengine.cpp | 13 +++++++++++++
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/src/qml/qml/v8/qqmlbuiltinfunctions.cpp b/src/qml/qml/v8/qqmlbuiltinfunctions.cpp
index d634a48443..f5e723419e 100644
--- a/src/qml/qml/v8/qqmlbuiltinfunctions.cpp
+++ b/src/qml/qml/v8/qqmlbuiltinfunctions.cpp
@@ -1553,11 +1553,12 @@ static QString jsStack(QV4::ExecutionEngine *engine) {
     return stack;
 }
 
-static QString serializeArray(Object *array, ExecutionEngine *v4) {
+static QString serializeArray(Object *array, ExecutionEngine *v4, QSet<QV4::Heap::Object *> &alreadySeen) {
     Scope scope(v4);
     ScopedValue val(scope);
     QString result;
 
+    alreadySeen.insert(array->d());
     result += QLatin1Char('[');
     const uint length = array->getLength();
     for (uint i = 0; i < length; ++i) {
@@ -1565,12 +1566,15 @@ static QString serializeArray(Object *array, ExecutionEngine *v4) {
             result += QLatin1Char(',');
         val = array->get(i);
         if (val->isManaged() && val->managed()->isArrayLike())
-            result += serializeArray(val->objectValue(), v4);
+            if (!alreadySeen.contains(val->objectValue()->d()))
+                result += serializeArray(val->objectValue(), v4, alreadySeen);
+            else
+                result += QLatin1String("[Circular]");
         else
             result += val->toQStringNoThrow();
     }
     result += QLatin1Char(']');
-
+    alreadySeen.remove(array->d());
     return result;
 };
 
@@ -1600,8 +1604,9 @@ static ReturnedValue writeToConsole(const FunctionObject *b, const Value *, cons
         if (i != start)
             result.append(QLatin1Char(' '));
 
+        QSet<QV4::Heap::Object *> alreadySeenElements;
         if (argv[i].isManaged() && argv[i].managed()->isArrayLike())
-            result.append(serializeArray(argv[i].objectValue(), v4));
+            result.append(serializeArray(argv[i].objectValue(), v4, alreadySeenElements));
         else
             result.append(argv[i].toQStringNoThrow());
     }
diff --git a/tests/auto/qml/qjsengine/tst_qjsengine.cpp b/tests/auto/qml/qjsengine/tst_qjsengine.cpp
index 56d2ce8730..b9df69d2db 100644
--- a/tests/auto/qml/qjsengine/tst_qjsengine.cpp
+++ b/tests/auto/qml/qjsengine/tst_qjsengine.cpp
@@ -258,6 +258,7 @@ private slots:
 
     void tostringRecursionCheck();
     void arrayIncludesWithLargeArray();
+    void printCircularArray();
 
 public:
     Q_INVOKABLE QJSValue throwingCppMethod1();
@@ -5054,6 +5055,18 @@ void tst_QJSEngine::arrayIncludesWithLargeArray()
     QCOMPARE(value.toBool(), false);
 }
 
+void tst_QJSEngine::printCircularArray()
+{
+    QJSEngine engine;
+    engine.installExtensions(QJSEngine::ConsoleExtension);
+    QTest::ignoreMessage(QtMsgType::QtDebugMsg, "[[Circular]]");
+    auto value = engine.evaluate(R"js(
+    let v1 = []
+    v1.push(v1)
+    console.log(v1)
+    )js");
+}
+
 QTEST_MAIN(tst_QJSEngine)
 
 #include "tst_qjsengine.moc"
-- 
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