Add QJSEngine::throwError() method to report run-time errors

It is quite common in JavaScript to use exceptions for error handling, but
there was no way to generate an exception from C++ context, i.e. when
the JS run-time invoked a C++ method or a slot.

This patch adds an naive way to report run-time errors to QJSEngine from
CPP context. The user may set a custom error message, but the location
points always to the caller context in JavaScript.

[ChangeLog][QtQml][QJSEngine] Added API to throw run-time errors.

Task-number: QTBUG-39041
Change-Id: If59627b83d50351eb225adde63187fc251aa349e
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 35 insertions, 0 deletions

diff --git a/tests/auto/qml/qjsengine/tst_qjsengine.cpp b/tests/auto/qml/qjsengine/tst_qjsengine.cpp
index 796d9e9c34..c20937f9a1 100644
--- a/tests/auto/qml/qjsengine/tst_qjsengine.cpp
+++ b/tests/auto/qml/qjsengine/tst_qjsengine.cpp
@@ -219,6 +219,11 @@ private slots:
     void protoChanges_QTBUG68369();
     void multilineStrings();
 
+    void throwError();
+
+public:
+    Q_INVOKABLE QJSValue throwingCppMethod();
+
 signals:
     void testSignal();
 };
@@ -4291,6 +4296,36 @@ void tst_QJSEngine::multilineStrings()
 
 }
 
+void tst_QJSEngine::throwError()
+{
+    QJSEngine engine;
+    QJSValue wrappedThis = engine.newQObject(this);
+    QQmlEngine::setObjectOwnership(this, QQmlEngine::CppOwnership);
+    engine.globalObject().setProperty("testCase", wrappedThis);
+
+    QJSValue result = engine.evaluate(
+                "function test(){\n"
+                "try {\n"
+                "    return testCase.throwingCppMethod();\n"
+                "} catch (error) {\n"
+                "    return error;\n"
+                "}\n"
+                "return \"not reached!\";\n"
+                "}\n"
+                "test();"
+    );
+    QVERIFY(result.isError());
+    QCOMPARE(result.property("lineNumber").toString(), "3");
+    QCOMPARE(result.property("message").toString(), "blub");
+    QVERIFY(!result.property("stack").isUndefined());
+}
+
+QJSValue tst_QJSEngine::throwingCppMethod()
+{
+    qjsEngine(this)->throwError("blub");
+    return QJSValue(47);
+}
+
 QTEST_MAIN(tst_QJSEngine)
 
 #include "tst_qjsengine.moc"