Error message to indicate if there are no validators (#2099)

### Description

Adds a more descriptive error message for failing to reach validator
quorum when there are no validators defined.

### Drive-by changes

No

### Related issues

- Fixes #2031 

### Backward compatibility

_Are these changes backward compatible?_

Yes

_Are there any infrastructure implications, e.g. changes that would
prohibit deploying older commits using this infra tooling?_

None


### Testing

_What kind of testing have these changes undergone?_

None

rust/agents/relayer/src/msg/metadata/base.rs

@@ -1,22 +1,22 @@
-use async_trait::async_trait;
-use hyperlane_core::accumulator::merkle::Proof;
-use num_derive::FromPrimitive;
-use num_traits::FromPrimitive;
 use std::str::FromStr;
 use std::sync::Arc;
 use std::{collections::HashMap, fmt::Debug};
 
+use async_trait::async_trait;
 use derive_new::new;
 use eyre::{Context, Result};
+use num_derive::FromPrimitive;
+use num_traits::FromPrimitive;
 use tokio::sync::RwLock;
 use tracing::{debug, instrument, warn};
 
 use hyperlane_base::{
     ChainConf, CheckpointSyncer, CheckpointSyncerConf, CoreMetrics, MultisigCheckpointSyncer,
 };
+use hyperlane_core::accumulator::merkle::Proof;
 use hyperlane_core::{
-    HyperlaneMessage, MultisigIsm, MultisigSignedCheckpoint, RoutingIsm, ValidatorAnnounce, H160,
-    H256,
+    HyperlaneDomain, HyperlaneMessage, MultisigIsm, MultisigSignedCheckpoint, RoutingIsm,
+    ValidatorAnnounce, H160, H256,
 };
 
 use crate::merkle_tree_builder::MerkleTreeBuilder;
@@ -41,11 +41,8 @@ pub enum SupportedIsmTypes {
 #[async_trait]
 pub trait MetadataBuilder: Send + Sync {
     #[allow(clippy::async_yields_async)]
-    async fn build(
-        &self,
-        ism_address: H256,
-        message: &HyperlaneMessage,
-    ) -> eyre::Result<Option<Vec<u8>>>;
+    async fn build(&self, ism_address: H256, message: &HyperlaneMessage)
+        -> Result<Option<Vec<u8>>>;
 }
 
 #[derive(Clone, new)]
@@ -78,7 +75,7 @@ impl MetadataBuilder for BaseMetadataBuilder {
         &self,
         ism_address: H256,
         message: &HyperlaneMessage,
-    ) -> eyre::Result<Option<Vec<u8>>> {
+    ) -> Result<Option<Vec<u8>>> {
         const CTX: &str = "When fetching module type";
         let ism = self
             .chain_setup
@@ -106,7 +103,11 @@ impl MetadataBuilder for BaseMetadataBuilder {
 }
 
 impl BaseMetadataBuilder {
-    pub fn clone_with_incremented_depth(&self) -> eyre::Result<BaseMetadataBuilder> {
+    pub fn domain(&self) -> &HyperlaneDomain {
+        &self.chain_setup.domain
+    }
+
+    pub fn clone_with_incremented_depth(&self) -> Result<BaseMetadataBuilder> {
         let mut cloned = self.clone();
         cloned.depth += 1;
         if cloned.depth > cloned.max_depth {
@@ -162,7 +163,7 @@ impl BaseMetadataBuilder {
     pub async fn build_checkpoint_syncer(
         &self,
         validators: &[H256],
-    ) -> eyre::Result<MultisigCheckpointSyncer> {
+    ) -> Result<MultisigCheckpointSyncer> {
         let storage_locations = self
             .validator_announce
             .get_announced_storage_locations(validators)

rust/agents/relayer/src/msg/metadata/multisig.rs

@@ -1,14 +1,14 @@
-use async_trait::async_trait;
-use ethers::abi::Token;
-use hyperlane_core::accumulator::merkle::Proof;
 use std::collections::HashMap;
 use std::fmt::Debug;
 use std::ops::Deref;
 
+use async_trait::async_trait;
 use derive_new::new;
+use ethers::abi::Token;
 use eyre::Context;
 use tracing::{debug, info, instrument};
 
+use hyperlane_core::accumulator::merkle::Proof;
 use hyperlane_core::{
     HyperlaneMessage, MultisigIsm, MultisigSignedCheckpoint, SignatureWithSigner, H256,
 };
@@ -48,10 +48,18 @@ impl MetadataBuilder for MultisigIsmMetadataBuilder {
         let Some(checkpoint) = self.fetch_checkpoint(&validators, threshold.into(), message)
             .await.context(CTX)?
         else {
-            info!(
-                ?validators, threshold,
-                "Could not fetch metadata: Unable to reach quorum"
-            );
+            if validators.is_empty() {
+                info!(
+                    ism=%multisig_ism.address(),
+                    chain=%self.base.domain().name(),
+                    "Could not fetch metadata: No validator set for chain is configured on the recipient's ISM"
+                );
+            } else {
+                info!(
+                    ?validators, threshold, ism=%multisig_ism.address(),
+                    "Could not fetch metadata: Unable to reach quorum"
+                );
+            }
             return Ok(None);
         };