add two checks to make sure we never update the protobuf files

coding.go

@@ -13,6 +13,11 @@ import (
 	ipld "github.com/ipfs/go-ipld-format"
 )
 
+// Make sure the user doesn't upgrade this file.
+// We need to check *here* as well as inside the `pb` package *just* in case the
+// user replaces *all* go files in that package.
+const _ = pb.DoNotUpgradeFileEverItWillChangeYourHashes
+
 // for now, we use a PBNode intermediate thing.
 // because native go objects are nice.
 

pb/merkledag.pb.go

@@ -31,6 +31,15 @@ import strconv "strconv"
 
 import bytes "bytes"
 
+// DoNotUpgradeFileEverItWillChangeYourHashes warns users about not breaking
+// their file hashes.
+const DoNotUpgradeFileEverItWillChangeYourHashes = `
+This file does not produce canonical protobufs. Unfortunately, if we change it,
+we'll change the hashes of the files we produce.
+
+Do *not regenerate this file.
+`
+
 // Reference imports to suppress errors if they are not otherwise used.
 var _ = proto.Marshal
 var _ = math.Inf

pb/upgrade_check.go

+package merkledag_pb
+
+// Make sure the user doesn't upgrade this package!
+// This will fail to build if the user does.
+const _ = DoNotUpgradeFileEverItWillChangeYourHashes