It appears that inside BLOCK, the type of x is unknown and there is no type inference. Am I doing something wrong, or is this just the way things are with IntelliJ's dealing with the futures::select! macro ?
Actually, since this is due to the use of proc macros, I wonder if Tokio's select! works better here, as that macro uses a declarative macro rather than a proc macro. I don't have IntelliJ myself, so I can't really test it.