Add a cache to file path mapping (#1228)

* Add a cache to file path mapping
This greatly reduces the time needed to resolve FilePathKey objects on watch builds.

* Address PR comments

* Bump package.json and CHANGELOG.md

Co-authored-by: John Reilly <johnny_reilly@hotmail.com>

CHANGELOG.md

@@ -1,4 +1,6 @@
 # Changelog
+## v8.0.13
+* [Speed up builds by adding an in-memory cache to file path lookups](https://github.com/TypeStrong/ts-loader/pull/1228) - thanks @berickson1
 
 ## v8.0.12
 * [Instead of checking date, check time thats more accurate to see if something has changed](https://github.com/TypeStrong/ts-loader/pull/1217) - thanks @sheetalkamat

package.json

@@ -1,6 +1,6 @@
 {
   "name": "ts-loader",
-  "version": "8.0.12",
+  "version": "8.0.13",
   "description": "TypeScript loader for webpack",
   "main": "index.js",
   "types": "dist",

src/instances.ts

@@ -87,23 +87,35 @@ function createFilePathKeyMapper(
   compiler: typeof typescript,
   loaderOptions: LoaderOptions
 ) {
+  // Cache file path key - a map lookup is much faster than filesystem/regex operations & the result will never change
+  const filePathMapperCache = new Map<string, FilePathKey>();
   // FileName lowercasing copied from typescript
   const fileNameLowerCaseRegExp = /[^\u0130\u0131\u00DFa-z0-9\\/:\-_\. ]+/g;
   return useCaseSensitiveFileNames(compiler, loaderOptions)
     ? pathResolve
     : toFileNameLowerCase;
 
-  function pathResolve(x: string) {
-    return path.resolve(x) as FilePathKey;
+  function pathResolve(filePath: string) {
+    let cachedPath = filePathMapperCache.get(filePath);
+    if (!cachedPath) {
+      cachedPath = path.resolve(filePath) as FilePathKey;
+      filePathMapperCache.set(filePath, cachedPath);
+    }
+    return cachedPath;
   }
 
-  function toFileNameLowerCase(x: string) {
-    const filePathKey = pathResolve(x);
-    return fileNameLowerCaseRegExp.test(filePathKey)
-      ? (filePathKey.replace(fileNameLowerCaseRegExp, ch =>
-          ch.toLowerCase()
-        ) as FilePathKey)
-      : filePathKey;
+  function toFileNameLowerCase(filePath: string) {
+    let cachedPath = filePathMapperCache.get(filePath);
+    if (!cachedPath) {
+      const filePathKey = pathResolve(filePath);
+      cachedPath = fileNameLowerCaseRegExp.test(filePathKey)
+        ? (filePathKey.replace(fileNameLowerCaseRegExp, ch =>
+            ch.toLowerCase()
+          ) as FilePathKey)
+        : filePathKey;
+      filePathMapperCache.set(filePath, cachedPath);
+    }
+    return cachedPath;
   }
 }