From 4d62faad02827d543dd8da7b605d3e3c972e36e0 Mon Sep 17 00:00:00 2001
From: David Michon <dmichon@microsoft.com>
Date: Tue, 16 Jul 2024 15:55:34 -0700
Subject: [PATCH] [heft] Handle errors when IPC messaging host (#4832)

Co-authored-by: David Michon <dmichon-msft@users.noreply.github.com>
---
 .../main_2024-07-15-21-27.json                | 10 ++++++++++
 libraries/operation-graph/src/WatchLoop.ts    | 20 ++++++++++++++++---
 2 files changed, 27 insertions(+), 3 deletions(-)
 create mode 100644 common/changes/@rushstack/operation-graph/main_2024-07-15-21-27.json

diff --git a/common/changes/@rushstack/operation-graph/main_2024-07-15-21-27.json b/common/changes/@rushstack/operation-graph/main_2024-07-15-21-27.json
new file mode 100644
index 00000000000..789587ea170
--- /dev/null
+++ b/common/changes/@rushstack/operation-graph/main_2024-07-15-21-27.json
@@ -0,0 +1,10 @@
+{
+  "changes": [
+    {
+      "packageName": "@rushstack/operation-graph",
+      "comment": "Handle errors when sending IPC messages to host.",
+      "type": "patch"
+    }
+  ],
+  "packageName": "@rushstack/operation-graph"
+}
\ No newline at end of file
diff --git a/libraries/operation-graph/src/WatchLoop.ts b/libraries/operation-graph/src/WatchLoop.ts
index 99b9e31537c..ca911c32bf7 100644
--- a/libraries/operation-graph/src/WatchLoop.ts
+++ b/libraries/operation-graph/src/WatchLoop.ts
@@ -133,6 +133,20 @@ export class WatchLoop implements IWatchLoopState {
       let runRequestedFromHost: boolean = true;
       let status: OperationStatus = OperationStatus.Ready;
 
+      function tryMessageHost(
+        message: ISyncEventMessage | IRequestRunEventMessage | IAfterExecuteEventMessage
+      ): void {
+        if (!host.send) {
+          return reject(new Error('Host does not support IPC'));
+        }
+
+        try {
+          host.send(message);
+        } catch (err) {
+          reject(new Error(`Unable to communicate with host: ${err}`));
+        }
+      }
+
       function requestRunFromHost(requestor?: string): void {
         if (runRequestedFromHost) {
           return;
@@ -145,7 +159,7 @@ export class WatchLoop implements IWatchLoopState {
           requestor
         };
 
-        host.send!(requestRunMessage);
+        tryMessageHost(requestRunMessage);
       }
 
       function sendSync(): void {
@@ -153,7 +167,7 @@ export class WatchLoop implements IWatchLoopState {
           event: 'sync',
           status
         };
-        host.send!(syncMessage);
+        tryMessageHost(syncMessage);
       }
 
       host.on('message', async (message: CommandMessageFromHost) => {
@@ -189,7 +203,7 @@ export class WatchLoop implements IWatchLoopState {
                 event: 'after-execute',
                 status
               };
-              host.send!(afterExecuteMessage);
+              tryMessageHost(afterExecuteMessage);
             }
             return;
           }