[BUG] git stash pop --quiet deletes files in git 2.24.0

[Grzegorz Rajchman <rayman17@gmail.com>]

Hi, this is the first time I report an issue in git so I hope I'm
doing it right.

I have experienced some unexpected behaviour with git stash pop
--quiet in git 2.24.0. I use stash in a pre-commit hook script. In it,
I stash non-staged changes to keep the working directory clean while
running some linters, then I restore the stash by running pop, but
after the recent git update I noticed that it stages all previously
checked files as deleted.

Steps to reproduce:

  mkdir test-git-stash
  cd test-git-stash/
  git init
  echo foo > foo.txt
  git add . && git commit -m 'init'
  echo bar > foo.txt
  git stash save --quiet --include-untracked --keep-index
  git stash pop --quiet
  git status

This will unexpectedly output:

  On branch master
  Changes to be committed:
    (use "git restore --staged <file>..." to unstage)
      deleted:    foo.txt

  Untracked files:
    (use "git add <file>..." to include in what will be committed)
      foo.txt

Notice that foo.txt was staged as deleted whilst still being present
on the disk.

However, if I remove --quiet flag from stash pop:

  git restore --staged foo.txt
  git stash save --quiet --include-untracked --keep-index
  git stash pop
  git status

Then it works as expected. It used to work as expected in git prior to 2.24.0

My OS is Ubuntu 19.04.