From this section:

Logging methods cannot be generic.

This seems to be an unnecessary restriction that also works against the whole notion of high-performance logging.

I would like to be able to write a logging method like so:

[LoggerMessage(0, LogLevel.Trace, "C -> S {EndPoint}: {Channel}:{Code} ({Length} bytes)")]
public static partial void PacketReceived<TCode>(ILogger logger, IPEndPoint endPoint, ConnectionChannel channel, TCode code, int length)
    where TCode : struct, Enum;

Here, the type argument for TCode depends on the value of Channel. Of course, I could make the logging method non-generic and accept an Enum-typed value, but then I get unconditional boxing... certainly not what I want when logging in a fairly hot path. Alternatively, I could duplicate the method for as many TCodes as I have (which is what I'll do for now), but this is not great either, for all the expected maintenance reasons.

I think this restriction should just be lifted. Maybe there's a good reason for it, but if there is, it's not obvious to me.