I beleve it relates to the ESPAsyncWebServer library.
when building I am getting:
Looking for Hash library in registry
Warning! Library {u'platforms': [u'espressif8266'], u'name': u'Hash'} has not been found in PlatformIO Registry.
You can ignore this message, if {u'platforms': [u'espressif8266'], u'name': u'Hash'} is a built-in library (included in framework, SDK). E.g., SPI, Wire, etc.
The build finishes fine, but why am I getting this warning and how do I make it go?
The message can be ignored because Hash is indeed a library built into Arduino-ESP8266 (Arduino/libraries/Hash at master · esp8266/Arduino · GitHub). I think PlatformIO hasn’t scanned framework-internal libraries at this point and just tries to find the library in the PIO registry, which it doesn’t.
You can create an issue at Issues · platformio/platformio-core · GitHub to notify the developers of your request of changing / removing the message in wrong cases (If PIO can be 100% sure).