patch 8.1.0225: mode() does not indicate using CTRL-O from Insert mode

Problem:    Mode() does not indicate using CTRL-O from Insert mode.
Solution:   Add "niI", "niR" and "niV" to mode() result. (closes #3000)

runtime/doc/eval.txt

@@ -6224,32 +6224,38 @@ mode([expr])	Return a string that indicates the current mode.
 		a non-empty String (|non-zero-arg|), then the full mode is
 		returned, otherwise only the first letter is returned.
 
-			n	Normal, Terminal-Normal
+		   n	    Normal, Terminal-Normal
-			no	Operator-pending
+		   no	    Operator-pending
-			v	Visual by character
+		   niI	    Normal using |i_CTRL-O| in |Insert-mode|
-			V	Visual by line
+		   niR	    Normal using |i_CTRL-O| in |Replace-mode|
-			CTRL-V	Visual blockwise
+		   niV	    Normal using |i_CTRL-O| in |Virtual-Replace-mode|
-			s	Select by character
+		   v	    Visual by character
-			S	Select by line
+		   V	    Visual by line
-			CTRL-S	Select blockwise
+		   CTRL-V   Visual blockwise
-			i	Insert
+		   s	    Select by character
-			ic	Insert mode completion |compl-generic|
+		   S	    Select by line
-			ix	Insert mode |i_CTRL-X| completion
+		   CTRL-S   Select blockwise
-			R	Replace |R|
+		   i	    Insert
-			Rc	Replace mode completion |compl-generic|
+		   ic	    Insert mode completion |compl-generic|
-			Rv	Virtual Replace |gR|
+		   ix	    Insert mode |i_CTRL-X| completion
-			Rx	Replace mode |i_CTRL-X| completion
+		   R	    Replace |R|
-			c	Command-line editing
+		   Rc	    Replace mode completion |compl-generic|
-			cv	Vim Ex mode |gQ|
+		   Rv	    Virtual Replace |gR|
-			ce	Normal Ex mode |Q|
+		   Rx	    Replace mode |i_CTRL-X| completion
-			r	Hit-enter prompt
+		   c	    Command-line editing
-			rm	The -- more -- prompt
+		   cv	    Vim Ex mode |gQ|
-			r?	A |:confirm| query of some sort
+		   ce	    Normal Ex mode |Q|
-			!	Shell or external command is executing
+		   r	    Hit-enter prompt
-			t	Terminal-Job mode: keys go to the job
+		   rm	    The -- more -- prompt
+		   r?	    A |:confirm| query of some sort
+		   !	    Shell or external command is executing
+		   t	    Terminal-Job mode: keys go to the job
 		This is useful in the 'statusline' option or when used
 		with |remote_expr()| In most other places it always returns
 		"c" or "n".
+		Note that in the future more modes and more specific modes may
+		be added. It's better not to compare the whole string but only
+		the leading character(s).
 		Also see |visualmode()|.
 
 mzeval({expr})							*mzeval()*

src/evalfunc.c

@@ -8366,10 +8366,9 @@ f_mkdir(typval_T *argvars, typval_T *rettv)
     static void
 f_mode(typval_T *argvars, typval_T *rettv)
 {
-    char_u	buf[3];
+    char_u	buf[4];
 
-    buf[1] = NUL;
+    vim_memset(buf, 0, sizeof(buf));
-    buf[2] = NUL;
 
     if (time_for_testing == 93784)
     {
@@ -8435,6 +8434,12 @@ f_mode(typval_T *argvars, typval_T *rettv)
 	buf[0] = 'n';
 	if (finish_op)
 	    buf[1] = 'o';
+	else if (restart_edit == 'I' || restart_edit == 'R'
+							|| restart_edit == 'V')
+	{
+	    buf[1] = 'i';
+	    buf[2] = restart_edit;
+	}
     }
 
     /* Clear out the minor mode when the argument is not a non-zero number or

src/testdir/test_functions.vim

@@ -464,6 +464,18 @@ func Test_mode()
   call assert_equal('n', mode(0))
   call assert_equal('n', mode(1))
 
+  " i_CTRL-O
+  exe "normal i\<C-O>:call Save_mode()\<Cr>\<Esc>"
+  call assert_equal("n-niI", g:current_modes)
+
+  " R_CTRL-O
+  exe "normal R\<C-O>:call Save_mode()\<Cr>\<Esc>"
+  call assert_equal("n-niR", g:current_modes)
+
+  " gR_CTRL-O
+  exe "normal gR\<C-O>:call Save_mode()\<Cr>\<Esc>"
+  call assert_equal("n-niV", g:current_modes)
+
   " How to test operator-pending mode?
 
   call feedkeys("v", 'xt')

src/version.c

@@ -798,6 +798,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    225,
 /**/
     224,
 /**/