From f30a33858f23b6bc3c77fef44167e919c4925fdd Mon Sep 17 00:00:00 2001
From: zeertzjq <zeertzjq@outlook.com>
Date: Tue, 30 Sep 2025 09:06:09 +0800
Subject: [PATCH] vim-patch:9.1.1800: completion: strange behaviour with 'ac'
 completeopt=longest,preinsert

Problem:  completion: strange behaviour with 'ac'
          completeopt=longest,preinsert (zeertzjq)
Solution: Let preinsert take precedence (Girish Palya)

fixes: vim/vim#18410
closes: vim/vim#18428

https://github.com/vim/vim/commit/d35e5e4237ec578962d3d577bc5a4e4f6bf4abb2

Co-authored-by: Girish Palya <girishji@gmail.com>
---
 src/nvim/insexpand.c                       |  3 ++-
 test/functional/editor/completion_spec.lua |  6 +++---
 test/old/testdir/test_ins_complete.vim     | 12 +++++++++++-
 3 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/src/nvim/insexpand.c b/src/nvim/insexpand.c
index 9a4d978079..aed25df3b9 100644
--- a/src/nvim/insexpand.c
+++ b/src/nvim/insexpand.c
@@ -2736,7 +2736,8 @@ bool ins_compl_prep(int c)
   // Set "compl_get_longest" when finding the first matches.
   if (ctrl_x_mode_not_defined_yet()
       || (ctrl_x_mode_normal() && !compl_started)) {
-    compl_get_longest = (get_cot_flags() & kOptCotFlagLongest) != 0;
+    compl_get_longest = (get_cot_flags() & kOptCotFlagLongest) != 0
+                        && !ins_compl_has_autocomplete();
     compl_used_match = true;
   }
 
diff --git a/test/functional/editor/completion_spec.lua b/test/functional/editor/completion_spec.lua
index 80aea84b3e..7dfdb50be9 100644
--- a/test/functional/editor/completion_spec.lua
+++ b/test/functional/editor/completion_spec.lua
@@ -1496,18 +1496,18 @@ describe('completion', function()
 
     -- During delay wait, user can open menu using CTRL_N completion
     feed('<Esc>')
-    command('set completeopt=menuone,longest')
+    command('set completeopt=menuone')
     feed('Sf<C-N>')
     screen:expect([[
       foo                                                         |
       foobar                                                      |
       foobarbaz                                                   |
       foo^                                                         |
-      {4:foo            }{1:                                             }|
+      {12:foo            }{1:                                             }|
       {4:foobar         }{1:                                             }|
       {4:foobarbaz      }{1:                                             }|
       {1:~                                                           }|*2
-      {5:-- Keyword completion (^N^P) }{19:Back at original}               |
+      {5:-- Keyword completion (^N^P) }{6:match 1 of 3}                   |
     ]])
 
     -- After the menu is open, ^N/^P and Up/Down should not delay
diff --git a/test/old/testdir/test_ins_complete.vim b/test/old/testdir/test_ins_complete.vim
index ca365fbe08..d362c6ed83 100644
--- a/test/old/testdir/test_ins_complete.vim
+++ b/test/old/testdir/test_ins_complete.vim
@@ -5834,7 +5834,7 @@ func Test_autocompletedelay()
   call VerifyScreenDump(buf, 'Test_autocompletedelay_6', {})
 
   " During delay wait, user can open menu using CTRL_N completion
-  call term_sendkeys(buf, "\<Esc>:set completeopt=menuone,longest\<CR>")
+  call term_sendkeys(buf, "\<Esc>:set completeopt=menuone\<CR>")
   call term_sendkeys(buf, "Sf\<C-N>")
   call VerifyScreenDump(buf, 'Test_autocompletedelay_7', {})
 
@@ -5984,6 +5984,16 @@ func Test_autocomplete_longest()
   call feedkeys("Go\<ESC>", 'tx')
   call DoTest("f\<C-N>\<C-N>\<BS>\<BS>\<BS>\<BS>", 'foo', 3)
 
+  " Issue #18410: When both 'preinsert' and 'longest' are set, 'preinsert'
+  " takes precedence
+  %delete
+  set autocomplete completeopt+=longest,preinsert
+  call setline(1, ['foobar', 'foofoo', 'foobaz', ''])
+  call feedkeys("G", 'tx')
+  call DoTest("f", 'foobar', 2)
+  call assert_equal(1, g:preinserted)
+
+  " Undo
   %delete _
   let &l:undolevels = &l:undolevels
   normal! ifoo