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

@@ -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())

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.

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 : */

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

src/version.c

@@ -729,6 +729,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1827,
 /**/
     1826,
 /**/