here is updated version of this patch, calling the messages logical (decoding) messages consistently everywhere and removing any connection to standby messages. Moving this to it's own module gave me place to write some brief explanation about this so the code documentation has hopefully improved as well.
The functionality itself didn't change.
I'd like to mention that there is my upcoming patch which is named generic WAL records.
But it has to be distinct feature from your generic WAL logical messages. Theoretically, we could have generic messages with arbitrary content and both having custom WAL reply function and being decoded by output plugin. But custom WAL reply function would let extension bug break recovery, archiving and physical replication. And that doesn't seem to be acceptable. This is why we have to develop these as separate features.
Should we think more about naming? Does two kinds of generic records confuse people?
Logical messages
Generic WAL records
Seems like I can tell them apart. Worth checking, but I think we're OK.
I was worrying because topic name is "Generic WAL logical messages". But if we name them just "Logical messages" then it's OK for me.