From 638cf5b7b880f770fae8c3942352153a51f64965 Mon Sep 17 00:00:00 2001
From: Sheetal Nandi <shkamat@microsoft.com>
Date: Thu, 4 Oct 2018 15:55:17 -0700
Subject: [PATCH 1/2] Ignore the directory watchers invoked in non polling
 watch mode with no relative file name information Fixes #27326

---
 src/compiler/sys.ts | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/src/compiler/sys.ts b/src/compiler/sys.ts
index 713085f192..5aaa331f58 100644
--- a/src/compiler/sys.ts
+++ b/src/compiler/sys.ts
@@ -796,11 +796,10 @@ namespace ts {
                         dirName,
                         (_eventName: string, relativeFileName) => {
                             // When files are deleted from disk, the triggered "rename" event would have a relativefileName of "undefined"
-                            const fileName = !isString(relativeFileName)
-                                ? undefined! // TODO: GH#18217
-                                : getNormalizedAbsolutePath(relativeFileName, dirName);
+                            if (!isString(relativeFileName)) { return; }
+                            const fileName = getNormalizedAbsolutePath(relativeFileName, dirName);
                             // Some applications save a working file via rename operations
-                            const callbacks = fileWatcherCallbacks.get(toCanonicalName(fileName));
+                            const callbacks = fileName && fileWatcherCallbacks.get(toCanonicalName(fileName));
                             if (callbacks) {
                                 for (const fileCallback of callbacks) {
                                     fileCallback(fileName, FileWatcherEventKind.Changed);

From 585420e9fae2ee381ed64d7b92cd4b773f0d7ca3 Mon Sep 17 00:00:00 2001
From: Sheetal Nandi <shkamat@microsoft.com>
Date: Tue, 9 Oct 2018 08:42:27 -0700
Subject: [PATCH 2/2] Updated callback signature

---
 src/compiler/sys.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/compiler/sys.ts b/src/compiler/sys.ts
index 5aaa331f58..0f90748f3c 100644
--- a/src/compiler/sys.ts
+++ b/src/compiler/sys.ts
@@ -846,7 +846,7 @@ namespace ts {
                 }
             }
 
-            type FsWatchCallback = (eventName: "rename" | "change", relativeFileName: string) => void;
+            type FsWatchCallback = (eventName: "rename" | "change", relativeFileName: string | undefined) => void;
 
             function createFileWatcherCallback(callback: FsWatchCallback): FileWatcherCallback {
                 return (_fileName, eventKind) => callback(eventKind === FileWatcherEventKind.Changed ? "change" : "rename", "");