Fix UnhandledPromiseRejectionWarning in copy (#1058)

Author: RyanZim

lib/copy/copy.js

@@ -6,6 +6,7 @@ const { mkdirs } = require('../mkdirs')
 const { pathExists } = require('../path-exists')
 const { utimesMillis } = require('../util/utimes')
 const stat = require('../util/stat')
+const { asyncIteratorConcurrentProcess } = require('../util/async')
 
 async function copy (src, dest, opts = {}) {
  if (typeof opts === 'function') {
@@ -113,28 +114,20 @@ async function onDir (srcStat, destStat, src, dest, opts) {
  await fs.mkdir(dest)
  }
 
- const promises = []
-
- // loop through the files in the current directory to copy everything
- for await (const item of await fs.opendir(src)) {
+ // iterate through the files in the current directory to copy everything
+ await asyncIteratorConcurrentProcess(await fs.opendir(src), async (item) => {
  const srcItem = path.join(src, item.name)
  const destItem = path.join(dest, item.name)
 
- promises.push(
- runFilter(srcItem, destItem, opts).then(include => {
- if (include) {
- // only copy the item if it matches the filter function
- return stat.checkPaths(srcItem, destItem, 'copy', opts).then(({ destStat }) => {
- // If the item is a copyable file, `getStatsAndPerformCopy` will copy it
- // If the item is a directory, `getStatsAndPerformCopy` will call `onDir` recursively
- return getStatsAndPerformCopy(destStat, srcItem, destItem, opts)
- })
- }
- })
- )
- }
-
- await Promise.all(promises)
+ const include = await runFilter(srcItem, destItem, opts)
+ // only copy the item if it matches the filter function
+ if (include) {
+ const { destStat } = await stat.checkPaths(srcItem, destItem, 'copy', opts)
+ // If the item is a copyable file, `getStatsAndPerformCopy` will copy it
+ // If the item is a directory, `getStatsAndPerformCopy` will call `onDir` recursively
+ await getStatsAndPerformCopy(destStat, srcItem, destItem, opts)
+ }
+ })
 
  if (!destStat) {
  await fs.chmod(dest, srcStat.mode)

lib/util/async.js

@@ -0,0 +1,29 @@
+'use strict'
+
+// https://github.com/jprichardson/node-fs-extra/issues/1056
+// Performing parallel operations on each item of an async iterator is
+// surprisingly hard; you need to have handlers in place to avoid getting an
+// UnhandledPromiseRejectionWarning.
+// NOTE: This function does not presently handle return values, only errors
+async function asyncIteratorConcurrentProcess (iterator, fn) {
+ const promises = []
+ for await (const item of iterator) {
+ promises.push(
+ fn(item).then(
+ () => null,
+ (err) => err ?? new Error('unknown error')
+ )
+ )
+ }
+ await Promise.all(
+ promises.map((promise) =>
+ promise.then((possibleErr) => {
+ if (possibleErr !== null) throw possibleErr
+ })
+ )
+ )
+}
+
+module.exports = {
+ asyncIteratorConcurrentProcess
+}