__Custom Components file structure change:__ A significant change in how the "under the hood" of Home Assistant works has led to forcing platforms to be resolved based off the component path, if it exists.

Today, if you want, you can override the Hue light platform, but not the other parts of the Hue integration. If a future update evolves the Hue component, removing or changing internal methods that the custom platform relied upon, the custom platform will start failing ([like this report](https://github.com/home-assistant/home-assistant/issues/17943#issuecomment-462014778)).

To avoid this, we're going to __no longer allow custom components to be partial overlays__ (just a platform). Instead, if you want to override a built-in platform, __you will need to override the whole component__.

This is enforced by first resolving the platform as a component, and if it exists, limiting the lookup path to the component path.

Example: if I look up the hue component, and it is provided by a custom component, then all platform lookups will also be looked up in the custom component dir. The same works the other way around, if a user would only try to override `hue/light.py` but not` hue/__init__.py`, the custom platform will be ignored.

Paulus has written some detailed information about this change on the developers' blog, if you'd like more information. [The Great Migration by Paulus](https://developers.home-assistant.io/blog/2019/02/19/the-great-migration.html)

__Existing SmartThings configuration entries will be removed,__ including the SmartApp/Automation from the SmartThings app. Home Assistant will prompt you to configure the integration again or it can be invoked from the integrations page. The configuration process is the same as before. To prepare, have your _personal access token and a mobile device with the SmartThings Classic App handy._ This will not affect the naming of devices or entities and is a __one-time inconvenience.__ The implementation switches over to the SmartApp access token to synchronize subscriptions during setup of the config entry, which cannot be done using the personal access token.

- __HomeMatic component's wireless actors__ are having two RSSI values. The way the component was programmed one of them was being overwritten. With this new change, the __`rssi` attribute of HomeMatic entities has been removed.__ As a replacement the attributes rssi_device and rssi_peer have been added. The attribute of `rssi` will no longer be available, you'll need to __update to `rssi_device`,__ and you can add `rssi_peer` now as well! (fixes #20900) ([@dagobert] - [#20902]) ([homematic docs]) (breaking change)

- You can now specifiy an action when calling the __yeelight_start_flow service__ on your yeelights. The __default action will be 'recover'__ if you do not specify something else. This action will be taken after the flow stops. ([@zewelor] - [#21195]) ([light.yeelight docs]) (breaking change)

- Custom platforms that override a built-in platform that has a component, should now also include the component in the custom_components/ folder. So if you want to override `hue/light.py` with a custom version, __you will also need to provide/copy over `hue/__init__.py`.__ See details in main section about this change. ([@balloob] - [#21070]) (breaking change)

- Automatic discovery of __TP-Link switches, bulbs and dimmers.__ This is a continuation of #15329 and adds support for automatic discovery of TP-Link bulbs, switches, and dimmers based on the new config flow. The integration needs to be enabled either in the __integration configuration or__ alternatively by __adding tplink component__ to the configuration file. As the devices are now configured on the component, this is a __breaking change for light.tplink and switch.tplink.__ ([@rytilahti] - [#18091]) ([tplink docs]) ([light.tplink docs]) ([switch.tplink docs]) (breaking change)

- Enhance __SmartThings component__ subscription. See details in main section about this change. ([@andrewsayre] - [#21124]) ([smartthings docs]) (breaking change) (new-feature)

- The __iperf3 sensor platform__ has been __separated__ into a component and a sensor to remove the service from the sensor platform. Configuration options have changed, __please review the documentation__ and select the correct options. ([@rohankapoorcom] - [#21138]) ([iperf3 docs]) __([sensor.iperf3 docs])__ (breaking change) (new-platform)

- The __`google_travel_time`__ platform no longer has an update service, use __homeassistant.update with the appropriate entity_id(s) instead.__ ([@rohankapoorcom] - [#21153]) ([sensor.google_travel_time docs]) (breaking change)

- Add ADB server functionality to __Fire TV.__ This change __removes the `get_source`__ configuration option. ([@JeffLIrion] - [#21221]) ([media_player.firetv docs]) (breaking change)

- With the addition of the __SmartThings Cover__ platform, the SmartThings __Sensor platform will no longer represent Door, Garage Door and Window Share attributes.__ Additionally, if the cover device reports battery status, the value will be present as a __state attribute__ (battery_level) and not a discrete sensor. ([@andrewsayre] - [#21192]) ([cover docs]) ([smartthings docs]) (breaking change) (new-platform)

- The __Toon component__ was broken some time ago, so now requires a Toon API developer account and __can be configured using the Home Assistant integrations.__ Support for Switches & Smoke detectors has been removed. ([@frenck] - [#21186]) ([toon docs]) (breaking change) (new-platform)

- Addition of config for __trusted networks auth provider.__ It is a breaking changes for users who __manually configured__ trusted network auth provider. An invalid config error will be thrown and HA won't be able to fully started. (It is NOT a breaking changes for user who didn't manual configured trusted network auth provider.) ([@awarecan] - [#21111]) (breaking change)

- For some __HomeMatic devices the `sabotage` attribute is replaced by `error`.__ The value (if not 0) is a device specific error code. ([@dagobert] - [#21009]) ([homematic docs]) (breaking change)