Remove logic converting empty or falsy YAML to empty dict

[emontnemery]

Proposed change

Remove logic from yaml.loader.load_yaml converting "falsy" files to empty dict

Rationale: Empty files, or files containing falsy data such as the number 0, False, an empty list etc. are valid yaml and there's no reason why they should be converted to an empty dict.

It's however a common case that we do want to load configuration files which must be dictionaries and which we do allow to be empty.
Add a new helper yaml.loader.load_yaml_dict for this case which:

• Returns an empty dict if the file is empty
• Raises if the top level structure is not a dict
• Is typed and guaranteed to return a dict, so the caller does not need to check this

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
• I have followed the perfect PR recommendations
• The code has been formatted using Black (black --fast homeassistant tests)
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

If the code communicates with devices, web services, or third-party tools:

• The manifest file has all fields filled out correctly.
  Updated and included derived files by running: python3 -m script.hassfest.
• New or updated dependencies have been added to requirements_all.txt.
  Updated by running python3 -m script.gen_requirements_all.
• For the updated dependencies - a link to the changelog, or at minimum a diff between library versions is added to the PR description.
• Untested files have been added to .coveragerc.

To help with the load of incoming pull requests:

• I have reviewed two other open pull requests in this repository.

[emontnemery]

This seems like quite the hack, shouldn't the consumer handle this? We could also make our own extensions, i.e. !include and friends, do this conversion and document it.

[frenck]

This is kinda odd behavior in general, why would we map an empty files to an empty dict in the first place?

[emontnemery]

I think it's to make !include and friends more user friendly by treating an empty yaml file as an empty dictionary.

I think we should handle this in config.py though, not in our yaml loader.

Let's make this PR a draft until that's been clarified.

[balloob]

We did this indeed to ensure that the top-level data structure returend from a yaml.load is always a dictionary. Let's just say that we didn't always had config validation …

[jbouwh]

Nice catch,
Thnx @emontnemery 👍

[home-assistant]

Please take a look at the requested changes, and use the Ready for review button when you are done, thanks 👍

Learn more about our pull request process.

[MartinHjelmare]

I'm missing the reason for the refactor in the PR description.

[emontnemery]

I'm missing the reason for the refactor in the PR description.

PR description updated to motivate the changes

[MartinHjelmare]

Looks good!