From b6029eb6271e325045aab627f133095151d78016 Mon Sep 17 00:00:00 2001
From: Brent Erickson <berickson1@users.noreply.github.com>
Date: Wed, 10 Mar 2021 13:33:00 -0800
Subject: [PATCH 1/2] Optimize fileExists callback path Instead of looking up
 filePathKey twice, cache in in the local scope. This isn't a hugely expensive
 lookup path, but is a hot path on large project recompiles (especially after
 caches are blown away). Profiling shows that even the Map lookup shows
 non-trivial cache lookup aggregate time

---
 src/servicesHost.ts | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/src/servicesHost.ts b/src/servicesHost.ts
index 170d03918..2447ba419 100644
--- a/src/servicesHost.ts
+++ b/src/servicesHost.ts
@@ -683,10 +683,14 @@ export function makeSolutionBuilderHost(
     scriptRegex,
     loader,
     instance,
-    fileName =>
-      !!instance.files.has(filePathKeyMapper(fileName)) ||
-      !!instance.otherFiles.get(filePathKeyMapper(fileName)) ||
-      compiler.sys.fileExists(fileName),
+    fileName => {
+      const filePathKey = filePathKeyMapper(fileName);
+      return (
+        instance.files.has(filePathKey) ||
+        instance.otherFiles.has(filePathKey) ||
+        compiler.sys.fileExists(fileName)
+      );
+    },
     /*enableFileCaching*/ true
   );
 

From 2b8fc3c7a958867dcef720f0cc30b3e270ff727a Mon Sep 17 00:00:00 2001
From: Brent Erickson <berickson1@users.noreply.github.com>
Date: Wed, 10 Mar 2021 22:45:45 -0800
Subject: [PATCH 2/2] Update Changelog & package.json

---
 CHANGELOG.md | 3 +++
 package.json | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 96b67abfa..96a3e42a4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,8 @@
 # Changelog
 
+## v8.0.18
+* [Perf: Optimize fileExists callback path](https://github.com/TypeStrong/ts-loader/issues/1266) - thanks @berickson1
+
 ## v8.0.17
 * [Included correct webpack source location in emitted errors](https://github.com/TypeStrong/ts-loader/issues/1199) - thanks @lorenzodallavecchia
 
diff --git a/package.json b/package.json
index c13d40f41..b9760fb33 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "ts-loader",
-  "version": "8.0.17",
+  "version": "8.0.18",
   "description": "TypeScript loader for webpack",
   "main": "index.js",
   "types": "dist",