Describe the bug

minpac#update() alters 'cpo'.

To Reproduce

Run this shell command:

vim -Nu NONE -S <(cat <<'EOF'
    vim9script
    set pp=/tmp/.vim rtp=/tmp/.vim
    delete('/tmp/.vim', 'rf')
    system('git clone https://github.com/k-takata/minpac.git /tmp/.vim/pack/minpac/opt/minpac')
    packadd minpac
    minpac#init()
    minpac#add('k-takata/minpac', {type: 'opt'})
    set cpo=BceFsMny>
    var cpo = &cpo
    minpac#update()
    timer_start(1'000, (_) => {
        echom 'cpo BEFORE #update(): ' .. cpo
        echom 'cpo AFTER #update():  ' .. &cpo
    })
EOF
)

Wait for minpac#update() to finish, then run :mess to read the messages.

This is printed:

cpo BEFORE #update(): BceFsMny>
cpo AFTER #update():  aABceFs

Expected behavior

This is printed:

cpo BEFORE #update(): BceFsMny>
cpo AFTER #update():  BceFsMny>

Because minpac should not alter the value of 'cpo' as set by the user.

Environment

• Vim version: 8.2 Included patches: 1-2772
• OS: Ubuntu 16.04.7 LTS
• Terminal: xterm(367)

Additional context

I think the issue comes from autoload/minpac/job.vim which resets 'cpo' to its default Vim value, without restoring it at the end. Considering that no other other script in minpac resets 'cpo', I guess those 2 lines should be removed:

diff --git a/autoload/minpac/job.vim b/autoload/minpac/job.vim
index 219fabc..f6d7a86 100644
--- a/autoload/minpac/job.vim
+++ b/autoload/minpac/job.vim
@@ -24,9 +24,6 @@
 "   SOFTWARE.
 " }}}
 
-let s:save_cpo = &cpo
-set cpo&vim
-
 let s:jobidseq = 0
 let s:jobs = {} " { job, opts, type: 'vimjob|nvimjob'}
 let s:job_type_nvimjob = 'nvimjob'

If, for some reason, 'cpo' really need to be temporarily reset to its default value, then it should be restored at the end:

diff --git a/autoload/minpac/job.vim b/autoload/minpac/job.vim
index 219fabc..ec17d38 100644
--- a/autoload/minpac/job.vim
+++ b/autoload/minpac/job.vim
@@ -263,3 +263,5 @@ function! minpac#job#wait(jobids, ...) abort
     return s:job_wait(a:jobids, l:timeout)
 endfunction
 " }}}
+let &cpo = s:save_cpo
+unlet! s:save_cpo