eliminate large enum in prost

[xxchan]

❯ cargo clippy -p risingwave_pb
   Compiling risingwave_pb v2.3.0-alpha (/Users/xxchan/Projects/risingwave/src/prost)
warning: large size difference between variants
   --> src/prost/src/expr.rs:867:5
    |
867 | /     pub enum RexNode {
868 | |         #[prost(uint32, tag = "4")]
869 | |         InputRef(u32),
870 | |         #[prost(message, tag = "5")]
871 | |         Constant(super::super::data::Datum),
    | |         ----------------------------------- the second-largest variant contains at least 24 bytes
...   |
875 | |         Udf(super::UserDefinedFunction),
    | |         ------------------------------- the largest variant contains at least 248 bytes
876 | |         #[prost(message, tag = "8")]
877 | |         Now(NowRexNode),
878 | |     }
    | |_____^ the entire enum is at least 248 bytes
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#large_enum_variant
    = note: `#[warn(clippy::large_enum_variant)]` on by default
help: consider boxing the large fields to reduce the total size of the enum
    |
875 |         Udf(Box<super::UserDefinedFunction>),
    |             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

warning: large size difference between variants
    --> src/prost/src/expr.rs:1539:5
     |
1539 | /     pub enum Type {
1540 | |         #[prost(enumeration = "GeneralType", tag = "1")]
1541 | |         General(i32),
     | |         ------------ the second-largest variant contains at least 4 bytes
1542 | |         /// Deprecated since we have a new `aggregate2` variant.
...    |
1546 | |         Aggregate2(super::AggType),
     | |         -------------------------- the largest variant contains at least 600 bytes
1547 | |     }
     | |_____^ the entire enum is at least 600 bytes
     |
     = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#large_enum_variant
help: consider boxing the large fields to reduce the total size of the enum
     |
1546 |         Aggregate2(Box<super::AggType>),
     |                    ~~~~~~~~~~~~~~~~~~~

warning: large size difference between variants
   --> src/prost/src/meta.rs:826:5
    |
826 | /     pub enum RelationInfo {
827 | |         #[prost(message, tag = "1")]
828 | |         Table(super::super::catalog::Table),
    | |         ----------------------------------- the largest variant contains at least 904 bytes
829 | |         #[prost(message, tag = "2")]
...   |
834 | |         Index(super::super::catalog::Index),
    | |         ----------------------------------- the second-largest variant contains at least 184 bytes
...   |
838 | |         Subscription(super::super::catalog::Subscription),
839 | |     }
    | |_____^ the entire enum is at least 0 bytes
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#large_enum_variant
help: consider boxing the large fields to reduce the total size of the enum
    |
828 |         Table(Box<super::super::catalog::Table>),
    |               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

warning: large size difference between variants
   --> src/prost/src/meta.rs:916:5
    |
916 | /     pub enum Info {
917 | |         #[prost(message, tag = "4")]
918 | |         Database(super::super::catalog::Database),
919 | |         #[prost(message, tag = "5")]
...   |
922 | |         Function(super::super::catalog::Function),
    | |         ----------------------------------------- the second-largest variant contains at least 312 bytes
...   |
932 | |         Snapshot(super::MetaSnapshot),
    | |         ----------------------------- the largest variant contains at least 688 bytes
...   |
952 | |         Secret(super::super::catalog::Secret),
953 | |     }
    | |_____^ the entire enum is at least 688 bytes
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#large_enum_variant
help: consider boxing the large fields to reduce the total size of the enum
    |
932 |         Snapshot(Box<super::MetaSnapshot>),
    |                  ~~~~~~~~~~~~~~~~~~~~~~~~

warning: large size difference between variants
   --> src/prost/src/stream_plan.rs:290:5
    |
290 | /     pub enum StreamMessage {
291 | |         #[prost(message, tag = "1")]
292 | |         StreamChunk(super::super::data::StreamChunk),
293 | |         #[prost(message, tag = "2")]
294 | |         Barrier(super::Barrier),
    | |         ----------------------- the largest variant contains at least 320 bytes
295 | |         #[prost(message, tag = "3")]
296 | |         Watermark(super::Watermark),
    | |         --------------------------- the second-largest variant contains at least 104 bytes
297 | |     }
    | |_____^ the entire enum is at least 320 bytes
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#large_enum_variant
help: consider boxing the large fields to reduce the total size of the enum
    |
294 |         Barrier(Box<super::Barrier>),
    |                 ~~~~~~~~~~~~~~~~~~~

warning: large size difference between variants
   --> src/prost/src/stream_plan.rs:561:5
    |
561 | /     pub enum Inner {
562 | |         #[prost(message, tag = "1")]
563 | |         ValueState(ValueState),
    | |         ---------------------- the second-largest variant contains at least 0 bytes
564 | |         #[prost(message, tag = "3")]
565 | |         MaterializedInputState(MaterializedInputState),
    | |         ---------------------------------------------- the largest variant contains at least 976 bytes
566 | |     }
    | |_____^ the entire enum is at least 976 bytes
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#large_enum_variant
help: consider boxing the large fields to reduce the total size of the enum
    |
565 |         MaterializedInputState(Box<MaterializedInputState>),
    |                                ~~~~~~~~~~~~~~~~~~~~~~~~~~~

warning: large size difference between variants
    --> src/prost/src/stream_plan.rs:1273:5
     |
1273 | /     pub enum NodeBody {
1274 | |         #[prost(message, tag = "100")]
1275 | |         Source(super::SourceNode),
1276 | |         #[prost(message, tag = "101")]
...    |
1291 | |         HashJoin(super::HashJoinNode),
     | |         ----------------------------- the largest variant contains at least 4120 bytes
...    |
1319 | |         DynamicFilter(super::DynamicFilterNode),
     | |         --------------------------------------- the second-largest variant contains at least 2144 bytes
...    |
1367 | |         AsOfJoin(super::AsOfJoinNode),
1368 | |     }
     | |_____^ the entire enum is at least 0 bytes
     |
     = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#large_enum_variant
help: consider boxing the large fields to reduce the total size of the enum
     |
1291 |         HashJoin(Box<super::HashJoinNode>),
     |                  ~~~~~~~~~~~~~~~~~~~~~~~~

warning: large size difference between variants
   --> src/prost/src/stream_service.rs:168:5
    |
168 | /     pub enum Request {
169 | |         #[prost(message, tag = "1")]
170 | |         Init(InitRequest),
171 | |         #[prost(message, tag = "2")]
172 | |         InjectBarrier(super::InjectBarrierRequest),
    | |         ------------------------------------------ the largest variant contains at least 496 bytes
173 | |         #[prost(message, tag = "3")]
174 | |         RemovePartialGraph(RemovePartialGraphRequest),
    | |         --------------------------------------------- the second-largest variant contains at least 32 bytes
...   |
178 | |         ResetDatabase(ResetDatabaseRequest),
179 | |     }
    | |_____^ the entire enum is at least 496 bytes
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#large_enum_variant
help: consider boxing the large fields to reduce the total size of the enum
    |
172 |         InjectBarrier(Box<super::InjectBarrierRequest>),
    |                       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

[xxchan]

We need either tokio-rs/prost#1211 or tokio-rs/prost#1209 to do it elegantly