Bug: Trees presorted phantom self-nested dir

[theopak]

Prerequisites

• I have searched for duplicate or closed issues
• I have read the contributing guidelines

Describe the issue

preparePresortedFileTreeInput produces a phantom, self-nested directory when the presorted input contains a directory row (trailing slash) immediately followed by one of its descendants. The shared-prefix cache inside appendPresortedPaths records the parent's prefix paired with the leaf's depth (off by one), so the next path that hits the cache fast-path re-creates the leaf directory as a child of itself.

Reproduction

import { preparePresortedFileTreeInput } from '@pierre/trees';

// Presorted, canonical-order directory paths (trailing slashes = directories).
const input = preparePresortedFileTreeInput([
  '/home/user/photos/',
  '/home/user/photos/raw/',
]);
// Build a tree from `input` (e.g. new PathStore({ preparedInput: input }),
// or a FileTree) and enumerate the directory nodes.

Expected directories:

/home/  →  /home/user/  →  /home/user/photos/  →  /home/user/photos/raw/

Actual — an extra phantom branch appears:

/home/user/photos/photos/
/home/user/photos/photos/raw/

(Any parent dir followed by a deeper descendant sharing its prefix triggers it; deeper inputs like ['/a/b/', '/a/b/c/', '/a/b/c/d/'] compound it into /a/b/b/, /a/b/b/c/c/, …. prepareFileTreeInput is unaffected — only the presorted path.)

Suggested fix

In appendPresortedPaths (path-store/src/builder.js), the trailing-slash leaf branch creates the leaf directory node and increments currentDepth, but never advances segmentStart. The subsequent cachedDirPrefix/cachedDirDepth write then stores the parent prefix at the leaf's depth — inconsistent by one level. Advancing segmentStart past the leaf restores the invariant:

--- a/path-store/src/builder.js
+++ b/path-store/src/builder.js
@@ -236,6 +236,9 @@ appendPresortedPaths(paths, containsDirectories = null) {
 						});
 						stackTop++;
 						dirStack[stackTop] = nodeId;
+						// Advance past the leaf dir so the cachedDirPrefix/cachedDirDepth
+						// write below pairs the leaf's full path with the leaf's depth,
+						// not the parent prefix at the leaf depth (off by one).
+						segmentStart = endIndex + 1;
 					}
 					const directoryId = dirStack[stackTop];
 					if (directoryId === void 0) throw new Error(`Unable to resolve directory node for "${path}"`);

This makes the cache record the leaf directory's full path at the leaf's depth, matching the file-path branch's existing (correct) behavior.

What browser(s) are you seeing the problem on?

Chrome

What version of @pierre/diffs are you using?

1.0.0-beta.4

---

AI disclosure: issue written with assistance from Claude Opus 4.8 based on usage in my private codebase.