fix within on windows

src/files.ts

@@ -7,13 +7,8 @@ import {cwd} from "node:process";
 import {fileURLToPath} from "node:url";
 import {isEnoent} from "./error.js";
 
-export function toOsPath(path: string): string {
-  return path.split(sep).join(op.sep);
-}
-
-export function fromOsPath(path: string): string {
-  return path.split(op.sep).join(sep);
-}
+export const toOsPath = sep === op.sep ? (path: string) => path : (path: string) => path.split(sep).join(op.sep);
+export const fromOsPath = sep === op.sep ? (path: string) => path : (path: string) => path.split(op.sep).join(sep);
 
 /**
  * Returns the relative path from the current working directory to the given

src/path.ts

@@ -1,4 +1,6 @@
-import {dirname, isAbsolute, join, normalize, relative, resolve} from "node:path/posix";
+import op from "node:path";
+import {dirname, join, normalize, relative, resolve} from "node:path/posix";
+import {fromOsPath} from "./files.js";
 
 /**
  * Returns the normalized relative path from "/file/path/to/a" to
@@ -86,6 +88,7 @@ export function parseRelativeUrl(url: string): {pathname: string; search: string
 }
 
 export function within(root: string, path: string): boolean {
+  const {relative, normalize, resolve, isAbsolute} = op;
   path = relative(normalize(resolve(root)), normalize(resolve(path)));
   return !path.startsWith("..") && !isAbsolute(path);
 }