In stm32L4xx_hal_uart.c and usart.c for the HAL Driver version 1.10.0, a call to HAL_UART_IRQHandler returns back to the caller if no errors instead of HAL_UART_RxCpltCallback. This is contrary to the descriptive comments in the beginning of the driver source that says a callback is used for non-blocking mode. Non-blocking in DMA mode returns to a callback.
Unlike the HAL COMM_IT example I am using a 1 word buffer.
I have not checked other driver versions.