oh, so that's how 'go generate' works.

main.go

@@ -1,5 +1,7 @@
 package main
 
+//go:generate ./mkprotos
+
 import (
 	"compress/bzip2"
 	"flag"

message.go

@@ -9,6 +9,9 @@ import (
 	"github.com/jordanorelli/hyperstone/dota"
 )
 
+// message represents the top-level envelope in the dota replay format. Each
+// datum is contained within a message envelope. Each message envelope is at
+// most 1<<16 bytes.
 type message struct {
 	cmd        dota.EDemoCommands
 	tick       int64

mkprotos

@@ -6,6 +6,9 @@ echo "Did you update the GameTracking submodule? You want to do that."
 echo "clearing existing proto files in ./dota"
 rm dota/*.proto
 
+echo "clearing existing generated go files in ./dota"
+rm dota/*.pb.go
+
 echo "copying protos from GameTracking/Protobufs/dota"
 cp GameTracking/Protobufs/dota/*.proto ./dota