From f3d0d089074c4517b26ea3d2253eaae36c6212eb Mon Sep 17 00:00:00 2001
From: Girish Palya <girishji@gmail.com>
Date: Sun, 5 Oct 2025 13:14:10 +0000
Subject: [PATCH] patch 9.1.1827: completion: v9.1.1797 broke Ctrl-Y behaviour

Problem:  completion: v9.1.1797 broke Ctrl-Y behaviour
          (ddad431, after v9.1.1797)
Solution: Restore correct behaviour (Girish Palya).

closes: #18494

Signed-off-by: Girish Palya <girishji@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
---
 src/edit.c                        |  7 +++++--
 src/insexpand.c                   |  9 +++++++++
 src/proto/insexpand.pro           |  1 +
 src/testdir/test_ins_complete.vim | 21 +++++++++++++++++++++
 src/version.c                     |  2 ++
 5 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/src/edit.c b/src/edit.c
index d564e2c9e6..c544df46f9 100644
--- a/src/edit.c
+++ b/src/edit.c
@@ -693,12 +693,15 @@ edit(
 			&& stop_arrow() == OK)
 		{
 		    ins_compl_delete();
-		    ins_compl_insert(FALSE, !ins_compl_has_preinsert());
-		    if (ins_compl_preinsert_longest())
+		    if (ins_compl_preinsert_longest()
+			    && !ins_compl_is_match_selected())
 		    {
+			ins_compl_insert(FALSE, TRUE);
 			ins_compl_init_get_longest();
 			continue;
 		    }
+		    else
+			ins_compl_insert(FALSE, FALSE);
 		}
 		// Delete preinserted text when typing special chars
 		else if (IS_WHITE_NL_OR_NUL(c) && ins_compl_preinsert_effect())
diff --git a/src/insexpand.c b/src/insexpand.c
index 38b2095632..40ba818668 100644
--- a/src/insexpand.c
+++ b/src/insexpand.c
@@ -853,6 +853,15 @@ is_nearest_active(void)
 	&& !(flags & COT_FUZZY);
 }
 
+/*
+ * TRUE if a match is selected (even if it is not inserted).
+ */
+    int
+ins_compl_is_match_selected(void)
+{
+    return compl_shown_match != NULL && !is_first_match(compl_shown_match);
+}
+
 /*
  * Returns TRUE if autocomplete is active and the pre-insert effect targets the
  * longest prefix.
diff --git a/src/proto/insexpand.pro b/src/proto/insexpand.pro
index 31d1ccb351..bff291171f 100644
--- a/src/proto/insexpand.pro
+++ b/src/proto/insexpand.pro
@@ -77,4 +77,5 @@ int ins_complete(int c, int enable_pum);
 void ins_compl_enable_autocomplete(void);
 void free_insexpand_stuff(void);
 void f_preinserted(typval_T *argvars, typval_T *rettv);
+int ins_compl_is_match_selected(void);
 /* vim: set ft=c : */
diff --git a/src/testdir/test_ins_complete.vim b/src/testdir/test_ins_complete.vim
index c2465030dd..a340d476e6 100644
--- a/src/testdir/test_ins_complete.vim
+++ b/src/testdir/test_ins_complete.vim
@@ -6036,4 +6036,25 @@ func Test_autocompletedelay_longest_preinsert()
   call StopVimInTerminal(buf)
 endfunc
 
+" Issue 18493
+func Test_longest_preinsert_accept()
+  call test_override("char_avail", 1)
+  new
+  call setline(1, ['func1', 'xfunc', 'func2'])
+  set completeopt+=noselect
+
+  call feedkeys("Gof\<C-N>\<Down>\<C-Y>", 'tx')
+  call assert_equal('func1', getline('.'))
+
+  set completeopt+=longest autocomplete
+  call feedkeys("Sf\<Down>\<C-Y>", 'tx')
+  call assert_equal('func2', getline('.'))
+  call feedkeys("Sf\<C-Y>", 'tx')
+  call assert_equal('func', getline('.'))
+
+  set completeopt& autocomplete&
+  bw!
+  call test_override("char_avail", 0)
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab nofoldenable
diff --git a/src/version.c b/src/version.c
index 6680030645..81368c1c9e 100644
--- a/src/version.c
+++ b/src/version.c
@@ -729,6 +729,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1827,
 /**/
     1826,
 /**/