Add subentry support for MQTT date, datetime and time entity platforms

[jbouwh]

Proposed change

Add subentry support for MQTT date, datetime and time entities

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: Add MQTT subentry support for date, datetime and time platform home-assistant.io#45454
• Link to developer documentation pull request:
• Link to frontend pull request:

Checklist

• I understand the code I am submitting and can explain how it works.
• 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 Ruff (ruff format homeassistant tests)
• Tests have been added to verify that the new code works.
• Any generated code has been carefully reviewed for correctness and compliance with project standards.

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 diff between library versions and ideally a link to the changelog/release notes is added to the PR description.

To help with the load of incoming pull requests:

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

[home-assistant]

Hey there @emontnemery, @bdraco, mind taking a look at this pull request as it has been labeled with an integration (mqtt) you are listed as a code owner for? Thanks!

Code owner commands

Code owners of mqtt can trigger bot actions by commenting:

• @home-assistant close Closes the pull request.
• @home-assistant mark-draft Mark the pull request as draft.
• @home-assistant ready-for-review Remove the draft status from the pull request.
• @home-assistant rename Awesome new title Renames the pull request.
• @home-assistant reopen Reopen the pull request.
• @home-assistant unassign mqtt Removes the current integration label and assignees on the pull request, add the integration domain after the command.
• @home-assistant update-branch Update the pull request branch with the base branch.
• @home-assistant add-label needs-more-information Add a label (needs-more-information, problem in dependency, problem in custom component, problem in config, problem in device, feature-request) to the pull request.
• @home-assistant remove-label needs-more-information Remove a label (needs-more-information, problem in dependency, problem in custom component, problem in config, problem in device, feature-request) on the pull request.

[Copilot]

Pull request overview

This PR extends the MQTT integration’s device subentry/config-flow support to include date, datetime, and time entities, aligning UI-driven subentry creation/migration with the platforms already supported by MQTT.

Changes:

• Added MQTT device subentry platform support for date, datetime, and time in the MQTT config flow, including required MQTT field definitions.
• Introduced a shared CONF_TIMEZONE constant for MQTT datetime configuration and exposed a timezone field in the config flow/strings.
• Expanded config flow migration tests and common test fixtures to cover the new subentry platforms.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
homeassistant/components/mqtt/config_flow.py	Adds date/datetime/time to subentry platforms, defines their MQTT field requirements, and introduces a timezone help URL placeholder.
homeassistant/components/mqtt/const.py	Adds CONF_TIMEZONE constant for shared use within the MQTT integration.
homeassistant/components/mqtt/datetime.py	Switches to importing CONF_TIMEZONE from MQTT constants instead of defining it locally.
homeassistant/components/mqtt/strings.json	Adds UI label/help text for timezone and enables date/datetime/time in the subentry platform selector strings.
tests/components/mqtt/common.py / tests/components/mqtt/test_config_flow.py	Adds fixtures and parametrized migration tests for date/datetime/time subentries.

[Copilot]

Copilot encountered an error and was unable to review this pull request. You can try again by re-requesting a review.