vim-patch:9.1.1820: completion: some issues with 'acl' (#36007)

Problem:  completion: some issues with 'acl' when "preinsert" and
          "longest" is in 'completeopt' (musonius, after v9.1.1638)
Solution: Fix various issues (see details below) (Girish Palya)

This commit addresses multiple issues in the 'autocompletedelay' behavior with
"preinsert" and "longest":

- Prevents spurious characters from being inserted.
- Ensures the completion menu is not shown until `autocompletedelay` has
  expired.
- Shows the "preinsert" effect immediately.
- Keeps the "preinsert" effect visible even when a character is deleted.

fixes: vim/vim#18443
closes: vim/vim#18460

f77c187277

Co-authored-by: Girish Palya <girishji@gmail.com>

test/old/testdir/test_ins_complete.vim

@@ -5869,7 +5869,7 @@ func Test_autocomplete_longest()
   call Ntest_override("char_avail", 1)
   new
   inoremap <buffer><F5> <C-R>=GetLine()<CR>
-  set completeopt=longest autocomplete
+  set completeopt+=longest autocomplete
   call setline(1, ["foobar", "foozbar"])
   call feedkeys("Go\<ESC>", 'tx')
 
@@ -6109,4 +6109,45 @@ func Test_refresh_always_with_fuzzy()
   call Ntest_override("char_avail", 0)
 endfunc
 
+func Test_autocompletedelay_longest_preinsert()
+  CheckScreendump
+  let lines =<< trim [SCRIPT]
+    call setline(1, ['autocomplete', 'autocomxxx'])
+    set autocomplete completeopt+=longest autocompletedelay=500
+  [SCRIPT]
+  call writefile(lines, 'XTest_autocompletedelay', 'D')
+  let buf = RunVimInTerminal('-S XTest_autocompletedelay', {'rows': 10})
+
+  " No spurious characters when autocompletedelay is in effect
+  call term_sendkeys(buf, "Goau")
+  sleep 10m
+  call term_sendkeys(buf, "toc")
+  sleep 100m
+  call VerifyScreenDump(buf, 'Test_autocompletedelay_longest_1', {})
+  sleep 500m
+  call VerifyScreenDump(buf, 'Test_autocompletedelay_longest_2', {})
+
+  " Deleting a char should still show longest text
+  call term_sendkeys(buf, "\<Esc>Saut")
+  sleep 10m
+  call term_sendkeys(buf, "\<BS>")
+  sleep 100m
+  call VerifyScreenDump(buf, 'Test_autocompletedelay_longest_3', {})
+  sleep 500m
+  call VerifyScreenDump(buf, 'Test_autocompletedelay_longest_4', {})
+
+  " Preinsert
+  call term_sendkeys(buf, "\<Esc>:set completeopt& completeopt+=preinsert\<CR>")
+
+  " Show preinserted text right away but display popup later
+  call term_sendkeys(buf, "\<Esc>Sau")
+  sleep 100m
+  call VerifyScreenDump(buf, 'Test_autocompletedelay_preinsert_1', {})
+  sleep 500m
+  call VerifyScreenDump(buf, 'Test_autocompletedelay_preinsert_2', {})
+
+  call term_sendkeys(buf, "\<esc>")
+  call StopVimInTerminal(buf)
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab nofoldenable