mkdirP: don't throw errors if windows drive exists

packages/io/__tests__/io.test.ts

@@ -864,6 +864,25 @@ describe('mkdirP', () => {
       (await fs.lstat(path.join(realDirPath, 'sub_dir'))).isDirectory()
     ).toBe(true)
   })
+
+  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:\\']) {
+        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
+          )
+        }
+      }
+    })
+  }
 })
 
 describe('which', () => {

packages/io/src/io.ts

@@ -141,7 +141,17 @@ export async function rmRF(inputPath: string): Promise<void> {
  */
 export async function mkdirP(fsPath: string): Promise<void> {
   ok(fsPath, 'a path argument must be provided')
-  await ioUtil.mkdir(fsPath, {recursive: true})
+  // 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})
+  }
 }
 
 /**