QML API 1.2: Handle JS exceptions in callbacks from Python

Also improve error message in pyotherside.send() callback handler
to include filename and line number.

docs/index.rst

@@ -44,6 +44,10 @@ io.thp.pyotherside 1.2
   for names with dots. This means that ``importModule('x.y.z', ...)`` now
   works like ``import x.y.z`` in Python.
 
+* If a JavaScript exception occurs in the callback passed to
+  :func:`importModule` or :func:`call`, the signal :func:`error` is emitted
+  with the exception information (filename, line, message) as ``traceback``.
+
 QML ``Python`` Element
 ----------------------
 
@@ -92,7 +96,7 @@ path and then importing the module asynchronously:
     ``file://`` from the path, so you can use :func:`Qt.resolvedUrl()`
     without having to manually strip the leading ``file://`` in QML.
 
-.. function:: importModule(string name, callable callback)
+.. function:: importModule(string name, function callback(success) {})
 
     Import a Python module.
 
@@ -102,6 +106,11 @@ path and then importing the module asynchronously:
     (``import io.thp.pyotherside 1.2``), this behavior is now fixed,
     and ``importModule('x.y.z, ...)`` behaves like ``import x.y.z``.
 
+.. versionchanged:: 1.2.0
+    If a JavaScript exception occurs in the callback, the :func:`error`
+    signal is emitted with ``traceback`` containing the exception info
+    (QML API version 1.2 and newer).
+
 Once modules are imported, Python function can be called on the
 imported modules using:
 
@@ -112,6 +121,11 @@ imported modules using:
     If ``callback`` is a callable, it will be called with the Python
     function result as single argument when the call has succeeded.
 
+.. versionchanged:: 1.2.0
+    If a JavaScript exception occurs in the callback, the :func:`error`
+    signal is emitted with ``traceback`` containing the exception info
+    (QML API version 1.2 and newer).
+
 For some of these methods, there also exist synchronous variants, but it is
 highly recommended to use the asynchronous variants instead to avoid blocking
 the QML UI thread:
@@ -698,6 +712,8 @@ Version 1.2.0dev (UNRELEASED)
 
 * Introduced versioned QML imports for API change.
 * QML API 1.2: Change :func:`importModule` behavior for imports with dots.
+* QML API 1.2: Emit :func:`error` when JavaScript callbacks passed to
+  :func:`importModule` and :func:`call` throw an exception.
 
 Version 1.1.0 (2014-02-06)
 --------------------------

src/qpython.cpp

@@ -27,6 +27,10 @@
 #include <QJSEngine>
 
 
+#define SINCE_API_VERSION(smaj, smin) \
+    ((api_version_major > smaj) || (api_version_major == smaj && api_version_minor >= smin))
+
+
 QPythonPriv *
 QPython::priv = NULL;
 
@@ -165,8 +169,10 @@ QPython::receive(QVariant variant)
             // 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()));
+            emit error("pyotherside.send() failed handler: " +
+                    result.property("fileName").toString() + ":" +
+                    result.property("lineNumber").toString() + ": " +
+                    result.toString());
         }
     } else {
         // Default action
@@ -265,7 +271,14 @@ QPython::finished(QVariant result, QJSValue *callback)
     QJSValueList args;
     QJSValue v = callback->engine()->toScriptValue(result);
     args << v;
-    callback->call(args);
+    QJSValue callbackResult = callback->call(args);
+    if (SINCE_API_VERSION(1, 2)) {
+        if (callbackResult.isError()) {
+            emit error(callbackResult.property("fileName").toString() + ":" +
+                    callbackResult.property("lineNumber").toString() + ": " +
+                    callbackResult.toString());
+        }
+    }
     delete callback;
 }
 
@@ -275,7 +288,14 @@ QPython::imported(bool result, QJSValue *callback)
     QJSValueList args;
     QJSValue v = callback->engine()->toScriptValue(QVariant(result));
     args << v;
-    callback->call(args);
+    QJSValue callbackResult = callback->call(args);
+    if (SINCE_API_VERSION(1, 2)) {
+        if (callbackResult.isError()) {
+            emit error(callbackResult.property("fileName").toString() + ":" +
+                    callbackResult.property("lineNumber").toString() + ": " +
+                    callbackResult.toString());
+        }
+    }
     delete callback;
 }
 

tests/test_callback_errors/test_callback_errors.qml

@@ -0,0 +1,41 @@
+import QtQuick 2.0
+import io.thp.pyotherside 1.2
+
+// Test if PyOtherSide correctly reports JS errors happening in callbacks
+// in signal error(string traceback) for both imports and function calls.
+
+Python {
+    property var tests: ([])
+
+    function test_next() {
+        if (tests.length) {
+            tests.pop()();
+        } else {
+            console.log('Tests done');
+            Qt.quit();
+        }
+    }
+
+    Component.onCompleted: {
+        tests.unshift(function () {
+            console.log('Expecting ReferenceError for "invalid" on import');
+            importModule('os', function (success) {
+                invalid;
+            });
+        });
+        tests.unshift(function() {
+            console.log('Expecting TypeError for "lock" property');
+            call('os.getcwd', [], function (result) {
+                console.lock(result);
+            });
+        });
+        test_next();
+    }
+
+    onError: {
+        // Remove full path to .qml file
+        var msg = traceback.replace(Qt.resolvedUrl('.'), '');
+        console.log('Got error: ' + msg);
+        test_next();
+    }
+}

tests/test_callback_errors/test_callback_errors.txt

@@ -0,0 +1,5 @@
+Expecting ReferenceError for "invalid" on import
+Got error: test_callback_errors.qml:23: ReferenceError: invalid is not defined
+Expecting TypeError for "lock" property
+Got error: test_callback_errors.qml:29: TypeError: Property 'lock' of object [object Object] is not a function
+Tests done