feat(move-file): add move fallback for weird errors

lib/util/move-file.js

@@ -1,9 +1,12 @@
 'use strict'
 
-var fs = require('graceful-fs')
+const fs = require('graceful-fs')
+const Promise = require('bluebird')
+let move
+let pinflight
 
 module.exports = moveFile
-function moveFile (src, dest, cb) {
+function moveFile (src, dest) {
   // This isn't quite an fs.rename -- the assumption is that
   // if `dest` already exists, and we get certain errors while
   // trying to move it, we should just not bother.
@@ -13,16 +16,35 @@ function moveFile (src, dest, cb) {
   // content their own way.
   //
   // Note that, as the name suggests, this strictly only supports file moves.
-  fs.link(src, dest, function (err) {
-    if (err) {
-      if (err.code === 'EEXIST' || err.code === 'EBUSY') {
-        // file already exists, so whatever
-      } else if (err.code === 'EPERM' && process.platform === 'win32') {
-        // file handle stayed open even past graceful-fs limits
-      } else {
-        return cb(err)
+  return Promise.fromNode(cb => {
+    fs.link(src, dest, err => {
+      if (err) {
+        if (err.code === 'EEXIST' || err.code === 'EBUSY') {
+          // file already exists, so whatever
+        } else if (err.code === 'EPERM' && process.platform === 'win32') {
+          // file handle stayed open even past graceful-fs limits
+        } else {
+          return cb(err)
+        }
       }
+      return fs.unlink(src, cb)
+    })
+  }).catch(err => {
+    if (process.platform !== 'win32') {
+      throw err
+    } else {
+      if (!pinflight) { pinflight = require('promise-inflight') }
+      return pinflight('cacache-move-file:' + dest, () => {
+        return Promise.promisify(fs.stat)(dest).catch(err => {
+          if (err !== 'ENOENT') {
+            // Something else is wrong here. Bail bail bail
+            throw err
+          }
+          // file doesn't already exist! let's try a rename -> copy fallback
+          if (!move) { move = require('@npmcorp/move') }
+          return move(src, dest, { Promise, fs })
+        })
+      })
     }
-    fs.unlink(src, cb)
   })
 }