fix(arborist): shrinkwrap throws when trying to read a folder without…

… permissions (npm#4258)

* fix(arborist): shrinkwrap throws trying to read a folder without permissions

Fix an issue where shrinkwrap throws an error when trying to read
a folder that it doesn't have permissions to, instead of returning
a correct object with an error

workspaces/arborist/lib/shrinkwrap.js

@@ -476,8 +476,13 @@ class Shrinkwrap {
       // all good!  hidden lockfile is the newest thing in here.
       return data
     }).catch(er => {
-      const rel = relpath(this.path, this.filename)
-      this.log.verbose('shrinkwrap', `failed to load ${rel}`, er)
+      /* istanbul ignore else */
+      if (typeof this.filename === 'string') {
+        const rel = relpath(this.path, this.filename)
+        this.log.verbose('shrinkwrap', `failed to load ${rel}`, er)
+      } else {
+        this.log.verbose('shrinkwrap', `failed to load ${this.path}`, er)
+      }
       this.loadingError = er
       this.loadedFromDisk = false
       this.ancientLockfile = false

workspaces/arborist/test/shrinkwrap.js

@@ -1597,4 +1597,19 @@ t.test('setting lockfileVersion from the file contents', async t => {
   })
 
   t.equal(Shrinkwrap.defaultLockfileVersion, 2, 'default is 2')
+
+  t.test('load should return error correctly when it cant access folder',
+    { skip: process.platform === 'win32' ? 'skip chmod in windows' : false },
+    async t => {
+      const dir = t.testdir({})
+      try {
+        fs.chmodSync(dir, '000')
+        const res = await Shrinkwrap.load({ path: dir })
+        t.ok(res.loadingError, 'loading error should exist')
+        t.strictSame(res.loadingError.errno, -13)
+        t.strictSame(res.loadingError.code, 'EACCES')
+      } finally {
+        fs.chmodSync(dir, '666')
+      }
+    })
 })