realpathSync('/') returns invalid result (edge case bug)

[williamstein]

This is easy to reproduce:

> memfs = require('memfs');
> memfs.vol.fromJSON({'./a':'a'}, '/');
> memfs.vol.realpathSync('/')
''

Notice that the output is an empty string, which isn't a valid path. This bug is caused by getPath() in node.ts:

  getPath(): string {
    return this.steps.join(SEP);
  }

The problem is the edge case of join when this.steps is [''], i.e., a list with a single empty string.

The following is what I would expect as output in this case:

> require('fs').realpathSync('/')
'/'

Perhaps a good fix would be:

  getPath(): string {
    const path = this.steps.join(SEP);
    return path ? path : "/";
  }

[williamstein]

My suggestion above breaks many tests. Here's an alternative that fixes this issue, and includes a jest test too (which passes):

diff --git a/src/__tests__/volume/realpathSync.test.ts b/src/__tests__/volume/realpathSync.test.ts
index 58d7746..251dfb3 100644
--- a/src/__tests__/volume/realpathSync.test.ts
+++ b/src/__tests__/volume/realpathSync.test.ts
@@ -1,6 +1,6 @@
 import { create } from '../util';
 
-describe('.realpath(...)', () => {
+describe('.realpathSync(...)', () => {
   it('works with symlinks, #463', () => {
     const vol = create({});
     vol.mkdirSync('/a');
@@ -12,3 +12,8 @@ describe('.realpath(...)', () => {
     expect(path).toBe('/c/index.js');
   });
 });
+
+describe("edge case -- realpathSync('/') returns '/'", () => {
+  const vol = create({'./a':'a'});
+  expect(vol.realpathSync('/')).toBe('/');
+});
\ No newline at end of file
diff --git a/src/volume.ts b/src/volume.ts
index 4f63532..b34860e 100644
--- a/src/volume.ts
+++ b/src/volume.ts
@@ -1493,7 +1493,8 @@ export class Volume {
     const realLink = this.getResolvedLink(steps);
     if (!realLink) throw createError(ENOENT, 'realpath', filename);
 
-    return strToEncoding(realLink.getPath(), encoding);
+    const path = realLink.getPath();
+    return strToEncoding(path ? path : "/", encoding);
   }
 
   realpathSync(path: PathLike, options?: IRealpathOptions | string): TDataOut {

[G-Rath]

@williamstein how would you feel about doing a PR? :)

[streamich]

🎉 This issue has been resolved in version 3.4.11 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀