Migration Guide

This page provides a guide for the changes necessary to switch between major versions of proto-lens.

0.4

Cabal configuration

In version 0.4, we have split proto-lens-protoc into several packages:

• proto-lens-protoc just contains the binary
• proto-lens-runtime contains the runtime libraries needed by generated code
• proto-lens-setup enables building custom Setup scripts. It depends on proto-lens-protoc.

To upgrade from v0.3 to v0.4:

• In the setup-depends field of the custom-setup clause, change proto-lens-protoc to proto-lens-setup.
• In the build-depends fields of libraries, tests and executables, change proto-lens-protoc to proto-lens-runtime.

See the README for more detailed instructions.

Proto construction

In proto-lens v0.3 and earlier, we used the def message from Data.Default.Class (from the data-default-class package) to construct default protobuf messages:

class Data.Default.Class.Default a => Message a where
    ...

In version 0.4, we have changed that to a custom method. (See #194 for the motivation). The new API is:

class Message a where
    defMessage :: a

Any previous code that tries to build a protobuf message with Data.Default.Class.def will break. There are two ways to fix this:

1. Replace all uses of def with defMessage. That method is exported from both Data.ProtoLens and Data.ProtoLens.Message.

2. (Simpler, legacy option): use Data.ProtoLens.Default.def, which is defined as

   def :: Message a => a
   def = defMessage
   

   That is, change any module imports from

   import Data.ProtoLens (def, encodeMessage, ...)
   

   to

   import Data.ProtoLens (encodeMessage, ...)
   import Data.ProtoLens.Default (def)
   

Command line flags

Direct users of protoc-gen-haskell (such as Bazel build rules) should change --no-reexports flag to --no-runtime.

Generated Instances

proto-lens-protoc now generates an explicit NFData instance for each protocol buffer message type. Any previously-added (orphan) instances of NFData should be removed.