From 067a1c4b7000a30fed4e7d9e467b594685efc1b3 Mon Sep 17 00:00:00 2001
From: Angela P Wen <angelapwen@github.com>
Date: Tue, 14 May 2024 15:56:18 +0000
Subject: [PATCH] Handle exit and error events for query server child processes

---
 .../src/query-server/query-server-client.ts   | 28 +++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

diff --git a/extensions/ql-vscode/src/query-server/query-server-client.ts b/extensions/ql-vscode/src/query-server/query-server-client.ts
index 2fb46471c55..c342e3b4996 100644
--- a/extensions/ql-vscode/src/query-server/query-server-client.ts
+++ b/extensions/ql-vscode/src/query-server/query-server-client.ts
@@ -240,8 +240,32 @@ export class QueryServerClient extends DisposableObject {
     this.nextCallback = 0;
     this.nextProgress = 0;
     this.progressCallbacks = {};
-    child.on("close", () => {
-      this.restartQueryServerOnFailure();
+
+    // 'exit' may or may not fire after 'error' event, so we want to guard against restarting the
+    // query server twice if both events fire.
+    let wasExitOrErrorHandled = false;
+    child.on("error", (err: Error) => {
+      if (!wasExitOrErrorHandled) {
+        void this.logger.log(`Query server terminated with error: ${err}.`);
+        this.restartQueryServerOnFailure();
+        wasExitOrErrorHandled = true;
+      }
+    });
+    child.on("exit", (code: number, signal: string) => {
+      if (!wasExitOrErrorHandled) {
+        if (code !== null) {
+          void this.logger.log(
+            `Query server terminated with exit code: ${code}.`,
+          );
+        }
+        if (signal !== null) {
+          void this.logger.log(
+            `Query server terminated due to receipt of signal: ${signal}.`,
+          );
+        }
+        this.restartQueryServerOnFailure();
+        wasExitOrErrorHandled = true;
+      }
     });
   }