feat: only hide/restore unstaged modifications to partially staged files

This change simplifies and speeds up the git workflow by restoring the backup stash before running tasks, and only doing diff/apply to files with both staged and unstaged changes. It also means that a file with only unstaged changes will be present on disk while the tasks are running, so for example unstaged edits to eslint rules will still apply.  This can be considered a fix because the behaviour changed from v9->v10, and this restores the previous behaviour.

lib/file.js

@@ -4,25 +4,10 @@ const debug = require('debug')('lint-staged:file')
 const fs = require('fs')
 const { promisify } = require('util')
 
-const fsAccess = promisify(fs.access)
 const fsReadFile = promisify(fs.readFile)
 const fsUnlink = promisify(fs.unlink)
 const fsWriteFile = promisify(fs.writeFile)
 
-/**
- * Check if a file exists. Returns the filename if exists.
- * @param {String} filename
- * @returns {String|Boolean}
- */
-const exists = async filename => {
-  try {
-    await fsAccess(filename)
-    return filename
-  } catch {
-    return false
-  }
-}
-
 /**
  * Read contents of a file to buffer
  * @param {String} filename
@@ -44,21 +29,19 @@ const readFile = async (filename, ignoreENOENT = true) => {
 }
 
 /**
- * Unlink a file if it exists
+ * Remove a file
  * @param {String} filename
  * @param {Boolean} [ignoreENOENT=true] — Whether to throw if the file doesn't exist
  */
 const unlink = async (filename, ignoreENOENT = true) => {
-  if (filename) {
-    debug('Unlinking file `%s`', filename)
-    try {
-      await fsUnlink(filename)
-    } catch (error) {
-      if (ignoreENOENT && error.code === 'ENOENT') {
-        debug("File `%s` doesn't exist, ignoring...", filename)
-      } else {
-        throw error
-      }
+  debug('Removing file `%s`', filename)
+  try {
+    await fsUnlink(filename)
+  } catch (error) {
+    if (ignoreENOENT && error.code === 'ENOENT') {
+      debug("File `%s` doesn't exist, ignoring...", filename)
+    } else {
+      throw error
     }
   }
 }
@@ -74,7 +57,6 @@ const writeFile = async (filename, buffer) => {
 }
 
 module.exports = {
-  exists,
   readFile,
   unlink,
   writeFile