From ca71c5242795aa666f7b47317394b30608eb397b Mon Sep 17 00:00:00 2001
From: Victor <70475442+vsolano9@users.noreply.github.com>
Date: Thu, 15 Oct 2026 17:24:07 +0200
Subject: [PATCH] fix(arborist): reuse a link target spelled with a different
 drive-letter case

On Windows, junctions keep the target spelling they were created with, so
links can name one directory as D:\pkg and d:\pkg. loadActual cached link
targets by the exact realpath string but placed nodes by a case-insensitive
relative location, so a second spelling built a duplicate target that evicted
the first and left its links without a target. Adding the next link then read
null.package in set root.

Reuse the node already at the target's inventory location before falling back
to the realpath cache.

Refs: #9079

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
---
 .../arborist/lib/arborist/load-actual.js      | 10 ++++--
 .../arborist/test/arborist/load-actual.js     | 34 +++++++++++++++++++
 2 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/workspaces/arborist/lib/arborist/load-actual.js b/workspaces/arborist/lib/arborist/load-actual.js
index 02a466e655aa6..4bf30db0d0725 100644
--- a/workspaces/arborist/lib/arborist/load-actual.js
+++ b/workspaces/arborist/lib/arborist/load-actual.js
@@ -13,6 +13,7 @@ const calcDepFlags = require('../calc-dep-flags.js')
 const Node = require('../node.js')
 const Link = require('../link.js')
 const realpath = require('../realpath.js')
+const relpath = require('../relpath.js')
 const PackageExtensions = require('../package-extensions.js')
 const NpmExtension = require('../npm-extension.js')
 
@@ -361,8 +362,13 @@ module.exports = cls => class ActualLoader extends cls {
   async #newLink (options) {
     const { realpath } = options
     this.#topNodes.add(realpath)
-    const target = this.#cache.get(realpath)
-    const link = new Link({ ...options, target })
+    // On Windows, links can spell one target differently (e.g. `D:\pkg` and `d:\pkg`).
+    // Those spellings share an inventory location, so a second target node there would evict
+    // the first and leave its links without a target. Reuse the node already at that location.
+    const root = options.root || options.parent?.root
+    const target = root?.inventory.get(relpath(root.realpath, realpath)) ||
+      this.#cache.get(realpath)
+    const link = new Link({ ...options, realpath: target?.path || realpath, target })
 
     if (!target) {
       // Link set its target itself in this case
diff --git a/workspaces/arborist/test/arborist/load-actual.js b/workspaces/arborist/test/arborist/load-actual.js
index 4552248b7ab94..fe59c632a8722 100644
--- a/workspaces/arborist/test/arborist/load-actual.js
+++ b/workspaces/arborist/test/arborist/load-actual.js
@@ -934,3 +934,37 @@ t.test('a project located under a .store path still loads its own devDependencie
   t.equal(tree.isInStore, false, 'loaded root is not flagged isInStore')
   t.ok(tree.edgesOut.get('a-dev-dep'), 'root devDependency is a required edge')
 })
+
+t.test('links that spell one target with different drive-letter case share it', {
+  skip: process.platform !== 'win32' && 'drive letters are Windows-only',
+}, async t => {
+  // Windows junctions keep the target spelling they were created with (npm/cli#9079).
+  const path = t.testdir({
+    pkg: { 'package.json': JSON.stringify({ name: 'pkg', version: '1.0.0' }) },
+    app: {
+      'package.json': JSON.stringify({
+        name: 'app',
+        version: '1.0.0',
+        dependencies: { a: 'file:../pkg', b: 'file:../pkg', c: 'file:../pkg' },
+      }),
+      node_modules: {},
+    },
+  })
+  const pkg = resolve(path, 'pkg')
+  const flipped = pkg[0] === pkg[0].toUpperCase()
+    ? pkg[0].toLowerCase() + pkg.slice(1)
+    : pkg[0].toUpperCase() + pkg.slice(1)
+  for (const [name, target] of [['a', pkg], ['b', flipped], ['c', pkg]]) {
+    fs.symlinkSync(target, resolve(path, 'app/node_modules', name), 'junction')
+  }
+
+  const tree = await loadActual(resolve(path, 'app'))
+  const links = ['a', 'b', 'c'].map(name => tree.children.get(name))
+  const [target] = links.map(link => link.target)
+  t.ok(target, 'links have a target')
+  t.equal(target.root, tree, 'the target is in the tree')
+  for (const link of links) {
+    t.equal(link.target, target, `${link.name} shares the target`)
+  }
+  t.equal(target.linksIn.size, 3, 'the target knows all three links')
+})