Use CosmosSdk as the chain type if omitted, for backward compatibility

Doing this requires a bit of hack, due to serde's lack of support
for specifying a default variant when a tag is not provided.

See the doc comment on the `ChainConfig` struct for more details.

config.toml

@@ -140,7 +140,8 @@ port = 5555
 # Specify the chain ID. Required
 id = 'ibc-0'
 
-# Specify the chain type, currently only `"CosmosSdk"` is supported.
+# Specify the chain type, currently only `CosmosSdk` is supported.
+# Default: CosmosSdk
 type = "CosmosSdk"
 
 # Whether or not this is a CCV consumer chain. Default: false
@@ -408,7 +409,6 @@ memo_prefix = ''
 
 [[chains]]
 id = 'ibc-1'
-type = "CosmosSdk"
 rpc_addr = 'http://127.0.0.1:26557'
 grpc_addr = 'http://127.0.0.1:9091'
 event_source = { mode = 'push', url = 'ws://127.0.0.1:26557/websocket', batch_delay = '500ms' }

crates/relayer-cli/src/chain_registry.rs

@@ -121,6 +121,7 @@ where
     };
 
     Ok(ChainConfig::CosmosSdk(CosmosSdkConfig {
+        r#type: Default::default(),
         id: chain_data.chain_id,
         rpc_addr: rpc_data.rpc_address,
         grpc_addr: grpc_address,

crates/relayer/Cargo.toml

@@ -70,6 +70,7 @@ strum = { version = "0.25", features = ["derive"] }
 tokio-stream = "0.1.14"
 once_cell = "1.19.0"
 tracing-subscriber = { version = "0.3.14", features = ["fmt", "env-filter", "json"] }
+monostate = "0.1.11"
 
 [dependencies.byte-unit]
 version = "4.0.19"

crates/relayer/src/chain/cosmos/config.rs

@@ -2,6 +2,7 @@ use core::time::Duration;
 use std::path::PathBuf;
 
 use byte_unit::Byte;
+use monostate::MustBe;
 use serde_derive::{Deserialize, Serialize};
 use tendermint_rpc::Url;
 
@@ -23,6 +24,11 @@ pub mod error;
 #[derive(Clone, Debug, PartialEq, Deserialize, Serialize)]
 #[serde(deny_unknown_fields)]
 pub struct CosmosSdkConfig {
+    /// The type of this chain, must be "CosmosSdk"
+    /// This is the default if not specified.
+    #[serde(default)]
+    pub r#type: MustBe!("CosmosSdk"),
+
     /// The chain's network identifier
     pub id: ChainId,
 

crates/relayer/src/config.rs

@@ -16,7 +16,7 @@ use core::time::Duration;
 use std::{fs, fs::File, io::Write, ops::Range, path::Path};
 
 use byte_unit::Byte;
-use serde_derive::{Deserialize, Serialize};
+use serde::{Deserialize, Serialize};
 use tendermint::block::Height as BlockHeight;
 use tendermint_rpc::Url;
 use tendermint_rpc::WebSocketClientUrl;
@@ -603,9 +603,18 @@ pub enum EventSourceMode {
     },
 }
 
+// NOTE:
+// To work around a limitation of serde, which does not allow
+// to specify a default variant if not tag is present,
+// every underlying chain config MUST have a field `r#type` of
+// type `monotstate::MustBe!("VariantName")`.
+//
+// For chains other than CosmosSdk, this field MUST NOT be annotated
+// with `#[serde(default)]`.
+//
+// See https://github.com/serde-rs/serde/issues/2231
 #[derive(Clone, Debug, PartialEq, Deserialize, Serialize)]
-#[serde(deny_unknown_fields)]
-#[serde(tag = "type")]
+#[serde(untagged)]
 pub enum ChainConfig {
     CosmosSdk(CosmosSdkConfig),
 }

tools/test-framework/src/types/single/node.rs

@@ -155,6 +155,7 @@ impl FullNode {
         };
 
         Ok(config::ChainConfig::CosmosSdk(CosmosSdkConfig {
+            r#type: Default::default(),
             id: self.chain_driver.chain_id.clone(),
             rpc_addr: Url::from_str(&self.chain_driver.rpc_address())?,
             grpc_addr: Url::from_str(&self.chain_driver.grpc_address())?,