LiveEditor crash if view interaction creates exception

[Tillsten]

Using the following code in the view and pressing the button crashs the editor.

from enaml.widgets.api import *
from enaml.layout.api import *

enamldef DemoContainer(Container):
    attr model
    PushButton:
        clicked :: model.foo

[frmdstryr]

What is the model?

[Tillsten]

The default one, which does not have a foo-member.

[frmdstryr]

Well I don't think this is a bug, it's just how Qt works.

Since the gui made with the editor runs in the same application as the editor itself you need to catch errors in the handler(s).

from enaml.widgets.api import *
from enaml.layout.api import *

enamldef DemoContainer(Container):
    attr model
    PushButton:
        clicked ::
            try:
                model.foo
            except Exception as e:
                print(e)

Then prints out this instead of exiting:

'NoneType' object has no attribute 'foo'

[Tillsten]

I think I understand why it does not work currently, but it may be possible to catch expections which originates from the the view? This the current hard-crashing behavior leads to code loss.

[frmdstryr]

This is Qt, not enaml... I think event handlers just need to catch errors.

See https://doc.qt.io/qt-5/exceptionsafety.html

Throwing an exception from a slot invoked by Qt's signal-slot connection mechanism is considered undefined behaviour, unless it is handled within the slot

Edit: Apologies for the snark remark... didn't mean't be rude.

[Tillsten]

IIRC throwing an exception in qt normally does not crash the program.

(skultrafast) c:\Users\tills\Downloads>enaml-run "live_editor(1).enaml"
Traceback (most recent call last):
  File "C:\Users\tills\miniconda3\envs\skultrafast\lib\site-packages\enaml\qt\qt_abstract_button.py", line 83, in on_clicked
    self.declaration.clicked(checked)
  File "C:\Users\tills\miniconda3\envs\skultrafast\lib\site-packages\enaml\core\declarative_meta.py", line 68, in declarative_change_handler
    engine.write(owner, change['name'], change)
  File "C:\Users\tills\miniconda3\envs\skultrafast\lib\site-packages\enaml\core\expression_engine.py", line 210, in write
    pair.writer(owner, name, change)
  File "C:\Users\tills\miniconda3\envs\skultrafast\lib\site-packages\enaml\core\standard_handlers.py", line 82, in __call__
    call_func(func, (), {}, scope)
  File "demo.enaml", line 8, in f
AttributeError: 'LiveEditorModel' object has no attribute 'i'

My issue is that currently if you write wrong code you lose everything.

[MatthieuDartiailh]

I will try to look into it. One option for the the example would be to set a custom handler in sys.excepthook and a recommendation in the applib documentation to do so when using it.