vim-patch:8.2.4090: after restoring a session buffer order can be quite different (#17112)

Problem:    After restoring a session buffer order can be quite different.
Solution:   Create buffers first. (Evgeni Chasnovski, closes vim/vim#9520)
https://github.com/vim/vim/commit/26ebf1f036517ebeacf571c333a83cca7e13bbe2

---------------
As in Vim, this basically reverts 8.1.0829 providing different solution
(see vim/vim#9520).

Regarding Neovim, this basically reverts changes from #15062. Test about
restoring same terminals was a bit too restrictive with using actual
buffer ids, which changed with this patch (now they should be in the
same order as at `mksession` call), so I tweaked it.

1 files changed, 25 insertions, 0 deletions

diff --git a/src/nvim/testdir/test_mksession.vim b/src/nvim/testdir/test_mksession.vim
index a87691abf9..a8e50af510 100644
--- a/src/nvim/testdir/test_mksession.vim
+++ b/src/nvim/testdir/test_mksession.vim
@@ -309,6 +309,31 @@ func Test_mksession_buffer_count()
   set nohidden
 endfunc
 
+func Test_mksession_buffer_order()
+  %bwipe!
+  e Xfoo | e Xbar | e Xbaz | e Xqux
+  bufdo write
+  mksession! Xtest_mks.out
+
+  " Verify that loading the session preserves order of buffers
+  %bwipe!
+  source Xtest_mks.out
+
+  let s:buf_info = getbufinfo()
+  call assert_true(s:buf_info[0]['name'] =~# 'Xfoo$')
+  call assert_true(s:buf_info[1]['name'] =~# 'Xbar$')
+  call assert_true(s:buf_info[2]['name'] =~# 'Xbaz$')
+  call assert_true(s:buf_info[3]['name'] =~# 'Xqux$')
+
+  " Clean up.
+  call delete('Xfoo')
+  call delete('Xbar')
+  call delete('Xbaz')
+  call delete('Xqux')
+  call delete('Xtest_mks.out')
+  %bwipe!
+endfunc
+
 if has('extra_search')
 
 func Test_mksession_hlsearch()