From 015c6a686d2d17f140b6417ef068c3c6cd8f327d Mon Sep 17 00:00:00 2001
From: JoostK <joost.koehoorn@gmail.com>
Date: Sun, 16 Aug 2020 13:17:06 +0200
Subject: [PATCH] fix(@angular-devkit/core): avoid RxJS performance penalty in
 sync fs calls

---
 .../angular_devkit/core/src/virtual-fs/host/sync.ts  | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/packages/angular_devkit/core/src/virtual-fs/host/sync.ts b/packages/angular_devkit/core/src/virtual-fs/host/sync.ts
index d28097c69bf1..cbc8629081cc 100644
--- a/packages/angular_devkit/core/src/virtual-fs/host/sync.ts
+++ b/packages/angular_devkit/core/src/virtual-fs/host/sync.ts
@@ -37,11 +37,13 @@ export class SyncDelegateHost<T extends object = {}> {
     let completed = false;
     let result: ResultT | undefined = undefined;
     let errorResult: Error | undefined = undefined;
-    observable.subscribe({
-      next(x: ResultT) { result = x; },
-      error(err: Error) { errorResult = err; },
-      complete() { completed = true; },
-    });
+    // Perf note: this is not using an observer object to avoid a performance penalty in RxJS.
+    // See https://github.com/ReactiveX/rxjs/pull/5646 for details.
+    observable.subscribe(
+      (x: ResultT) => result = x,
+      (err: Error) => errorResult = err,
+      () => completed = true,
+    );
 
     if (errorResult !== undefined) {
       throw errorResult;