Correct Windows path handling in new aspnet-webpack feature

Author: SteveSandersonMS

src/Microsoft.AspNetCore.SpaServices/npm/aspnet-webpack/package.json

@@ -1,6 +1,6 @@
 {
   "name": "aspnet-webpack",
-  "version": "1.0.19",
+  "version": "1.0.20",
   "description": "Helpers for using Webpack in ASP.NET Core projects. Works in conjunction with the Microsoft.AspNetCore.SpaServices NuGet package.",
   "main": "index.js",
   "scripts": {

src/Microsoft.AspNetCore.SpaServices/npm/aspnet-webpack/src/WebpackDevMiddleware.ts

@@ -124,7 +124,7 @@ function attachWebpackDevMiddleware(app: any, webpackConfig: webpack.Configurati
 
 function copyRecursiveSync(from: typeof fs, to: typeof fs, rootDir: string, exclude: RegExp[]) {
     from.readdirSync(rootDir).forEach(filename => {
-        const fullPath = path.join(rootDir, filename);
+        const fullPath = pathJoinSafe(rootDir, filename);
         const shouldExclude = exclude.filter(re => re.test(fullPath)).length > 0;
         if (!shouldExclude) {
             const fileStat = from.statSync(fullPath);
@@ -138,6 +138,17 @@ function copyRecursiveSync(from: typeof fs, to: typeof fs, rootDir: string, excl
     });
 }
 
+function pathJoinSafe(rootPath: string, filePath: string) {
+    // On Windows, MemoryFileSystem's readdirSync output produces directory entries like 'C:'
+    // which then trigger errors if you call statSync for them. Avoid this by detecting drive
+    // names at the root, and adding a backslash (so 'C:' becomes 'C:\', which works).
+    if (rootPath === '/' && path.sep === '\\' && filePath.match(/^[a-z0-9]+\:$/i)) {
+        return filePath + '\\';
+    } else {
+        return path.join(rootPath, filePath);
+    }
+}
+
 function beginWebpackWatcher(webpackConfig: webpack.Configuration) {
     const compiler = webpack(webpackConfig);
     compiler.watch({ /* watchOptions */ }, (err, stats) => {