Let PAHO MQTT client handle connection to MQTT server

[emontnemery]

Proposed change

Let PAHO MQTT client handle connection to MQTT server by itself, instead of doing checks when loading the config entry.
The checks prevents the config entry from loading until connection with the MQTT server is established, which breaks MQTT components as reported in #35858 as well as in other issues.

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)
• 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 MQTT devices fail to update if MQTT broker isn't ready on boot #35858

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
• 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.
• Untested files have been added to .coveragerc.

The integration reached or maintains the following Integration Quality Scale:

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[probot-home-assistant]

Hey there @home-assistant/core, mind taking a look at this pull request as its been labeled with a integration (mqtt) you are listed as a codeowner for? Thanks!
_{^{(message by CodeOwnersMention)}}

[MartinHjelmare]

Why doesn't the current retry logic work and a restart is required?

[emontnemery]

@MartinHjelmare The retry logic has already been removed, done in #34556
Edit: Or you mean why doesn't the retry logic for loading the config entry work?

[MartinHjelmare]

Yeah, the latter.

[emontnemery]

When the config entry is not loaded, calls to subscribe don't work so the subscriptions are not done once the connection to the MQTT server is established.
This breaks MQTT components, automations, etc. that setup subscriptions before the connection is established.

Since we don't unload the MQTT config entry if the connection is severed, I think it's OK to not block it from loading either?

[MartinHjelmare]

Why doesn't the subscription store work when the entry isn't setup?

[emontnemery]

The subscription store is reset every time loading the MQTT entry is retried because async_setup_entry will create a new MQTT instance:

core/homeassistant/components/mqtt/__init__.py

Line 630 in 5855246

hass.data[DATA_MQTT] = MQTT(

[MartinHjelmare]

Looks good! Just a small comment.

[MartinHjelmare]

Thanks!

[frenck]

/AzurePipelines run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[MartinHjelmare]

It's better to use the core interface, hass.config_entries.async_setup.