fix: reserve paths case-insensitively

The path reservation system prevents multiple file entries clobbering
one another while in flight, while allowing maximal parallelization
in unpacking otherwise.

However, on case-insensitive file systems, this can still introduce a
race condition if the entries in the archive have different cases, as
capital and lowercase entries will not be treated as reserving the same
path.

Normalize slashes and cases immediately when reserving paths, such that
paths which differ only in case or slash repetition are treated as
identical paths.

lib/path-reservations.js

@@ -8,6 +8,7 @@
 
 const assert = require('assert')
 const normPath = require('./normalize-windows-path.js')
+const { join } = require('path')
 
 module.exports = () => {
   // path => [function or Set]
@@ -19,9 +20,8 @@ module.exports = () => {
   const reservations = new Map()
 
   // return a set of parent dirs for a given path
-  const { join } = require('path')
   const getDirs = path =>
-    normPath(join(path)).split('/').slice(0, -1).reduce((set, path) =>
+    path.split('/').slice(0, -1).reduce((set, path) =>
       set.length ? set.concat(normPath(join(set[set.length - 1], path)))
       : [path], [])
 
@@ -99,6 +99,7 @@ module.exports = () => {
   }
 
   const reserve = (paths, fn) => {
+    paths = paths.map(p => normPath(join(p)).toLowerCase())
     const dirs = new Set(
       paths.map(path => getDirs(path)).reduce((a, b) => a.concat(b))
     )

test/path-reservations.js

@@ -49,7 +49,7 @@ t.test('basic race', t => {
   }
 
   t.ok(reserve(['a/b/c/d'], file), 'file starts right away')
-  t.notOk(reserve(['a/b/c/d', 'a/b/e'], link), 'link waits')
+  t.notOk(reserve(['a/B/c////D', 'a/b/e'], link), 'link waits')
   t.notOk(reserve(['a/b/e/f'], dir), 'dir waits')
   t.notOk(reserve(['a/b'], dir2), 'dir2 waits')
   t.notOk(reserve(['a/b/x'], dir3), 'dir3 waits')