Avoid exception when loading translation file for unloaded module

[awarecan]

Description:

There is a unhandled exception thrown if user navigate to config/integrations page in certain condition.

2018-07-31 09:29:25 ERROR (MainThread) [homeassistant.core] Error doing job: Task exception was never retrieved
Traceback (most recent call last):
  File "/home/jason/ha/home-assistant/homeassistant/components/frontend/__init__.py", line 495, in send_translations
    resources = await async_get_translations(hass, msg['language'])
  File "/home/jason/ha/home-assistant/homeassistant/helpers/translation.py", line 119, in async_get_translations
    resources = await async_get_component_resources(hass, language)
  File "/home/jason/ha/home-assistant/homeassistant/helpers/translation.py", line 98, in async_get_component_resources
    hass, component, language)
  File "/home/jason/ha/home-assistant/homeassistant/helpers/translation.py", line 39, in component_translation_file
    component_path = path.dirname(module.__file__)
AttributeError: 'NoneType' object has no attribute '__file__'

In my case, I disabled nest component in configuration.yaml, but didn't remove config entry from config, so it will cause nest component not loaded correctly. I am sure there may have other reason some module cannot be loaded correctly. In such scenario, all translation will be lost, screenshot likes

After this PR, only nest related translation will be lost, screenshot likes

Related issue (if applicable): fixes #

Pull request in home-assistant.github.io with documentation (if applicable): home-assistant/home-assistant.github.io#<home-assistant.github.io PR number goes here>

Example entry for configuration.yaml (if applicable):

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass

If the code does not interact with devices:

• Tests have been added to verify that the new code works.

[balloob]

This makes no sense. get_component is not about things not being setup. It's about loading the component from file, either from your custom components dir or from built-in.

[awarecan]

Alright, you are forcing me to fix the root cause. Got it.

[balloob]

This is also not good. We should fail. This code should never be called if filename is None.

We should write code that doesn't handle "bad" inputs and tries to fix them. Raise errors instead. The moment we fix them, that function will need to keep fixing it forever, even if other things get added to the function that would allow the previously bad input. The previously bad input expects to be "changed" or else bugs in other code happen.

[awarecan]

@balloob

I changed anther way to fix issue, but I am not sure I am doing right thing, the loader has pretty complex logic. Anyway, I got better result, even the nest component which has been failed during setup still get translation file loaded now.

[balloob]

How can this be None?

[awarecan]

https://github.com/home-assistant/home-assistant/blob/48af5116b34f1d19c5be2f913ae06831e871034f/homeassistant/setup.py#L165

Only place used loader.set_component method. Is that a legacy code?

[balloob]

That happens if a component is not correctly coded, we don't have such components in our code base. It's only when people are having badly written custom components, hence the warning.

[awarecan]

Root cause: home-assistant/architecture#52

[balloob]

I think you're misunderstanding the role of homeassistant.loader. The role of it is to load the actual files and return them as Python modules. It has to check if the user has a custom component and otherwise loads the built-in component/platform. Because it's doing I/O, the resolved module will be cached. This can never be None.

If you are having an import error, it means that you probably have a custom component and something is off.

[awarecan]

Aha, that is so tricky. Lesson learned. Closed this PR.