call mkdirP also when drive doesn't exist

packages/io/__tests__/io.test.ts

@@ -867,17 +867,16 @@ describe('mkdirP', () => {
 
   if (ioUtil.IS_WINDOWS) {
     it('show error only if Windows drive does not exist', async () => {
-      let errMsg: string
-      const driveRoot = path.parse(getTestTemp()).root
-      // Assuming 'A:\' is not a common Windows drive lets us test for a non-existing drive
-      for (const testPath of [driveRoot, 'A:\\']) {
+      const root = path.parse(getTestTemp()).root
+      // Assuming A:\ isn't a common Windows drive letter lets us test for a non-existing drive
+      const testPaths = [root, 'A:\\']
+      for (const testPath of testPaths) {
         if (await ioUtil.exists(testPath)) {
           await io.mkdirP(testPath)
         } else {
-          errMsg = `Drive '${testPath}' does not exist.`
           await expect(io.mkdirP(testPath)).rejects.toHaveProperty(
-            'message',
-            errMsg
+            'code',
+            'ENOENT'
           )
         }
       }

packages/io/src/io.ts

@@ -141,17 +141,16 @@ export async function rmRF(inputPath: string): Promise<void> {
  */
 export async function mkdirP(fsPath: string): Promise<void> {
   ok(fsPath, 'a path argument must be provided')
-  // mkdirP would throw EPERM error if `fsPath` is a Windows drive root dir, e.g. 'C:\'
-  // even when it exists. This aligns with node's fs.mkdir impl. However, mkdirP shouldn't
-  // throw errors if `fsPath` exists regardless of the underlying platform.
-  // In this case, we will only check if drive exists and throw an error if it doesn't.
-  if (ioUtil.IS_WINDOWS && path.parse(fsPath).root === fsPath) {
-    if (!(await ioUtil.exists(fsPath))) {
-      throw new Error(`Drive '${fsPath}' does not exist.`)
-    }
-  } else {
-    await ioUtil.mkdir(fsPath, {recursive: true})
+  // don't call mkdirP for root paths (e.g. C:\) on Windows. This leads to
+  // 'EPERM: operation not permitted' error when drive already exists.
+  if (
+    ioUtil.IS_WINDOWS &&
+    path.parse(fsPath).root === fsPath &&
+    (await ioUtil.exists(fsPath))
+  ) {
+    return
   }
+  await ioUtil.mkdir(fsPath, {recursive: true})
 }
 
 /**