Check JS callback errors. Fixes #9

Thanks to Osmo Salomaa for the original report and test case.

src/qpython.cpp

@@ -120,7 +120,17 @@ QPython::receive(QVariant variant)
         for (int i=1; i<list.size(); i++) {
             args << callback.engine()->toScriptValue(list[i]);
         }
-        callback.call(args);
+        QJSValue result = callback.call(args);
+        if (result.isError()) {
+            // Ideally we would throw the error back to Python (so that the
+            // pyotherside.send() method fails, as this is where the call
+            // originated). We can't do this, because the pyotherside.send()
+            // call is asynchronous (it returns before we call into JS), so do
+            // the next best thing and report the error to our error handler in
+            // QML instead.
+            emit error(QString("pyotherside.send() failed handler: %1")
+                    .arg(result.toString()));
+        }
     } else {
         // Default action
         emit received(variant);

tests/test_errors/README

@@ -0,0 +1,6 @@
+Test if JS errors from pyotherside.send() are propagated to the PyOtherSide
+error handler. Thanks to Osmo Salomaa for the original report and test case.
+
+----
+https://github.com/thp/pyotherside/issues/9
+https://gist.github.com/otsaloma/8258322

tests/test_errors/test_errors.py

@@ -0,0 +1,11 @@
+import pyotherside
+import threading
+import time
+
+def run():
+    while True:
+        pyotherside.send("test-errors")
+        time.sleep(3)
+
+thread = threading.Thread(target=run)
+thread.start()

tests/test_errors/test_errors.qml

@@ -0,0 +1,40 @@
+import QtQuick 2.0
+import io.thp.pyotherside 1.0
+
+Rectangle {
+    id: page
+    width: 300
+    height: 300
+
+    Component.onCompleted: {
+        py.addImportPath(Qt.resolvedUrl('.').substr('file://'.length));
+        py.setHandler("test-errors", page.testErrors);
+        py.importModule("test_errors", null);
+    }
+
+    Python {
+        id: py
+
+        onError: {
+            console.log("PYTHON ERROR: " + traceback);
+            msg.text += '\n' + traceback;
+        }
+    }
+
+    Text {
+        id: msg
+        anchors {
+            top: parent.top
+            left: parent.left
+            right: parent.right
+        }
+        text: "Testing (you should see errors appearing here)..."
+        wrapMode: Text.Wrap
+    }
+
+    function testErrors() {
+        console.log("starting");
+        page.nonexistentMethod();
+        console.log("finished");
+    }
+}