This is how API dispatching worked before this commit:
- The generated `msgpack_rpc_dispatch` function receives a the `msgpack_packer`
argument.
- The response is incrementally built while validating/calling the API.
- Return values/errors are also packed into the `msgpack_packer` while the
final response is being calculated.
Now the `msgpack_packer` argument is no longer provided, and the
`msgpack_rpc_dispatch` function returns `Object`/`Error` values to
`msgpack_rpc_call`, which will use those values to build the response in a
single pass.
This was done because the new `channel_send_call` function created the
possibility of having recursive API invocations, and this wasn't possible when
sharing a single `msgpack_sbuffer` across call frames(it was shared implicitly
through the `msgpack_packer` instance).
Since we only start to build the response when the necessary information has
been computed, it's now safe to share a single `msgpack_sbuffer` instance
across all channels and API invocations.
Some other changes also had to be performed:
- Handling of the metadata discover was moved to `msgpack_rpc_call`
- Expose more types as subtypes of `Object`, this was required to forward the
return value from `msgpack_rpc_dispatch` to `msgpack_rpc_call`
- Added more helper macros for casting API types to `Object`
any
When receiving strings *from* msgpack, we don't need to duplicate/free since
the data only lives in the msgpack parse buffer until the end of the call.
But in order to reuse `msgpack_rpc_free_object` when sending event data(which is
sent *to* msgpack), Strings must be freed, which means they must also be
allocated separately.
- Define specialized arrays for each remote object type
- Implement msgpack_rpc functions for dealing with the new types
- Refactor all functions dealing with buffers, windows and tabpages to
return/accept handles instead of list indexes.
