Explicitly shut down the build server when SourceKit-LSP is shut down

The build server is automatically shut down using a background task when `BuildSystemManager` is deallocated.

This, however, leads to possible race conditions where the shutdown task might not finish before the test is done, which could result in the connection being reported as a leak. To avoid this problem, we want to explicitly shut, down the build server when the `SourceKitLSPServer` gets shut down.

Author: ahoppen

Sources/BuildSystemIntegration/BuildSystemManager.swift

@@ -399,6 +399,23 @@ package actor BuildSystemManager: QueueBasedMessageHandler {
     }
   }
 
+  /// Explicitly shut down the build server.
+  ///
+  /// The build server is automatically shut down using a background task when `BuildSystemManager` is deallocated.
+  /// This, however, leads to possible race conditions where the shutdown task might not finish before the test is done,
+  /// which could result in the connection being reported as a leak. To avoid this problem, we want to explicitly shut
+  /// down the build server when the `SourceKitLSPServer` gets shut down.
+  package func shutdown() async {
+    guard let connectionToBuildSystem = await connectionToBuildSystem else {
+      return
+    }
+    await orLog("Sending shutdown request to build server") {
+      _ = try await connectionToBuildSystem.send(BuildShutdownRequest())
+      connectionToBuildSystem.send(OnBuildExitNotification())
+    }
+    _connectionToBuildSystem = nil
+  }
+
   deinit {
     // Shut down the build server before closing the connection to it
     Task { [connectionToBuildSystem = _connectionToBuildSystem, initializeResult] in

Sources/SourceKitLSP/SourceKitLSPServer.swift

@@ -1210,6 +1210,11 @@ extension SourceKitLSPServer {
           await service.shutdown()
         }
       }
+      for workspace in workspaces {
+        taskGroup.addTask {
+          await workspace.buildSystemManager.shutdown()
+        }
+      }
     }
 
     // We have a semantic guarantee that no request or notification should be