vim-patch:9.1.0207: No autocommand when writing session file (#28048)

Problem:  No autocommand when writing session file
Solution: Add SessionWritePost autocommand
          (Colin Kennedy)

fixes: vim/vim#14242
closes: vim/vim#14288

e5f2280381

Co-authored-by: Colin Kennedy <colinvfx@gmail.com>

test/old/testdir/test_autocmd.vim

@@ -3901,4 +3901,60 @@ func Test_autocmd_creates_new_buffer_on_bufleave()
   bw c.txt
 endfunc
 
+" Ensure `expected` was just recently written as a Vim session
+func s:assert_session_path(expected)
+  call assert_equal(a:expected, v:this_session)
+endfunc
+
+" Check for `expected` after a session is written to-disk.
+func s:watch_for_session_path(expected)
+  execute 'autocmd SessionWritePost * ++once execute "call s:assert_session_path(\"'
+        \ . a:expected
+        \ . '\")"'
+endfunc
+
+" Ensure v:this_session gets the full session path, if explicitly stated
+func Test_explicit_session_absolute_path()
+  %bwipeout!
+
+  let directory = getcwd()
+
+  let v:this_session = ""
+  let name = "some_file.vim"
+  let expected = fnamemodify(name, ":p")
+  call s:watch_for_session_path(expected)
+  execute "mksession! " .. expected
+
+  call delete(expected)
+endfunc
+
+" Ensure v:this_session gets the full session path, if explicitly stated
+func Test_explicit_session_relative_path()
+  %bwipeout!
+
+  let directory = getcwd()
+
+  let v:this_session = ""
+  let name = "some_file.vim"
+  let expected = fnamemodify(name, ":p")
+  call s:watch_for_session_path(expected)
+  execute "mksession! " .. name
+
+  call delete(expected)
+endfunc
+
+" Ensure v:this_session gets the full session path, if not specified
+func Test_implicit_session()
+  %bwipeout!
+
+  let directory = getcwd()
+
+  let v:this_session = ""
+  let expected = fnamemodify("Session.vim", ":p")
+  call s:watch_for_session_path(expected)
+  mksession!
+
+  call delete(expected)
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab