fix: update objMerge implementation (#4678)

### Description

Updating the `objMerge` implementation

A bug in the original implementation meant that the
`update-agent-config` script did _not_ overwrite the
`blocks.reorgPeriod` if there was a change, this new version does.

### Drive-by changes

- gracefully handle missing startBlock data when generating agent config
- fix objMerge calls that had the wrong order

### Related issues

definitely want to fix this bug before attempting to update our agent
configs with changes in
https://github.com/hyperlane-xyz/hyperlane-registry/pull/276

### Backward compatibility

should be, yes

### Testing

ci, manual testing when generating agent config files

.changeset/dirty-clocks-repeat.md

@@ -0,0 +1,5 @@
+---
+'@hyperlane-xyz/utils': patch
+---
+
+Fix objMerge implementation

typescript/cli/src/config/agent.ts

@@ -87,7 +87,7 @@ async function getStartBlocks(
   chainAddresses: ChainMap<ChainAddresses>,
   core: HyperlaneCore,
   chainMetadata: any,
-) {
+): Promise<ChainMap<number | undefined>> {
   return promiseObjAll(
     objMap(chainAddresses, async (chain, _) => {
       const indexFrom = chainMetadata[chain].index?.from;
@@ -103,6 +103,7 @@ async function getStartBlocks(
         errorRed(
           `❌ Failed to get deployed block to set an index for ${chain}, this is potentially an issue with rpc provider or a misconfiguration`,
         );
+        return undefined;
       }
     }),
   );

typescript/infra/scripts/agents/update-agent-config.ts

@@ -101,7 +101,7 @@ export async function writeAgentConfig(
             'Error:',
             err,
           );
-          return 0;
+          return undefined;
         }
       },
     ),

typescript/sdk/src/metadata/agentConfig.ts

@@ -418,7 +418,7 @@ export function buildAgentConfig(
   chains: ChainName[],
   multiProvider: MultiProvider,
   addresses: ChainMap<HyperlaneDeploymentArtifacts>,
-  startBlocks: ChainMap<number>,
+  startBlocks: ChainMap<number | undefined>,
   additionalConfig?: ChainMap<any>,
 ): AgentConfig {
   const chainConfigs: ChainMap<AgentChainMetadata> = {};
@@ -438,9 +438,11 @@ export function buildAgentConfig(
       ...metadata,
       ...addresses[chain],
       ...(additionalConfig ? additionalConfig[chain] : {}),
-      index: {
-        from: startBlocks[chain],
-      },
+      ...(startBlocks[chain] !== undefined && {
+        index: {
+          from: startBlocks[chain],
+        },
+      }),
     };
     chainConfigs[chain] = chainConfig;
   }

typescript/utils/src/objects.test.ts

@@ -35,6 +35,13 @@ describe('Object utilities', () => {
     expect(merged).to.eql({ a: 2, b: { c: ['arr2'] } });
   });
 
+  it('objMerge overwrites nested values', () => {
+    const obj1 = { a: { b: 10 }, c: 'value' };
+    const obj2 = { a: { b: 20 } };
+    const merged = objMerge(obj1, obj2);
+    expect(merged).to.eql({ a: { b: 20 }, c: 'value' });
+  });
+
   it('objOmit', () => {
     const obj1 = { a: 1, b: { c: ['arr1'], d: 'string' } };
     const obj2 = { a: true, b: { c: true } };

typescript/utils/src/objects.ts

@@ -99,8 +99,11 @@ export function pick<K extends string, V = any>(obj: Record<K, V>, keys: K[]) {
 }
 
 /**
- *  Returns a new object that recursively merges b into a
- *  Where there are conflicts, b takes priority over a
+ *  Returns a new object that recursively merges B into A
+ *  Where there are conflicts, B takes priority over A
+ *  If B has a value for a key that A does not have, B's value is used
+ *  If B has a value for a key that A has, and both are objects, the merge recurses into those objects
+ *  If B has a value for a key that A has, and both are arrays, the merge concatenates them with B's values taking priority
  * @param a - The first object
  * @param b - The second object
  * @param max_depth - The maximum depth to recurse
@@ -112,29 +115,34 @@ export function objMerge<T = any>(
   max_depth = 10,
   mergeArrays = false,
 ): T {
+  // If we've reached the max depth, throw an error
   if (max_depth === 0) {
     throw new Error('objMerge tried to go too deep');
   }
+  // If either A or B is not an object, return the other value
   if (!isObject(a) || !isObject(b)) {
-    return (b ? b : a) as T;
+    return (b ?? a) as T;
   }
-  const ret: Record<string, any> = {};
-  const aKeys = new Set(Object.keys(a));
-  const bKeys = new Set(Object.keys(b));
-  const allKeys = new Set([...aKeys, ...bKeys]);
-  for (const key of allKeys.values()) {
-    if (aKeys.has(key) && bKeys.has(key)) {
-      if (mergeArrays && Array.isArray(a[key]) && Array.isArray(b[key])) {
-        ret[key] = [...b[key], ...a[key]];
-      } else {
-        ret[key] = objMerge(a[key], b[key], max_depth - 1, mergeArrays);
-      }
-    } else if (aKeys.has(key)) {
-      ret[key] = a[key];
-    } else {
+  // Initialize returned object with values from A
+  const ret: Record<string, any> = { ...a };
+  // Iterate over keys in B
+  for (const key in b) {
+    // If both A and B have the same key, recursively merge the values from B into A
+    if (isObject(a[key]) && isObject(b[key])) {
+      ret[key] = objMerge(a[key], b[key], max_depth - 1, mergeArrays);
+    }
+    // If A & B are both arrays, and we're merging them, concatenate them with B's values taking priority before A
+    else if (mergeArrays && Array.isArray(a[key]) && Array.isArray(b[key])) {
+      ret[key] = [...b[key], ...a[key]];
+    }
+    // If B has a value for the key, set the value to B's value
+    // This better handles the case where A has a value for the key, but B does not
+    // In which case we want to keep A's value
+    else if (b[key] !== undefined) {
       ret[key] = b[key];
     }
   }
+  // Return the merged object
   return ret as T;
 }