feat(terminal): implement <c-\><c-o> for terminal mode

this works similar to <c-o> or <c-\><c-o> in insert mode

10 files changed, 86 insertions, 16 deletions

diff --git a/runtime/doc/builtin.txt b/runtime/doc/builtin.txt
index e2a8e098d2..61d04c6660 100644
--- a/runtime/doc/builtin.txt
+++ b/runtime/doc/builtin.txt
@@ -5311,6 +5311,7 @@ mode([expr])	Return a string that indicates the current mode.
 		   niV	    Normal using |i_CTRL-O| in |Virtual-Replace-mode|
 		   nt	    Normal in |terminal-emulator| (insert goes to
 				Terminal mode)
+		   ntT	    Normal using |t_CTRL-\_CTRL-O| in |terminal-mode|
 		   v	    Visual by character
 		   vs	    Visual by character using |v_CTRL-O| in Select mode
 		   V	    Visual by line
diff --git a/runtime/doc/index.txt b/runtime/doc/index.txt
index 25b98ae4ab..7d8a89887a 100644
--- a/runtime/doc/index.txt
+++ b/runtime/doc/index.txt
@@ -1101,8 +1101,11 @@ tag		command		action in Command-line editing mode	~
 5. Terminal mode				*terminal-mode-index*
 
 In a |terminal| buffer all keys except CTRL-\ are forwarded to the terminal
-job.  If CTRL-\ is pressed, the next key is forwarded unless it is CTRL-N.
+job.  If CTRL-\ is pressed, the next key is forwarded unless it is CTRL-N
+or CTRL-O.
 Use |CTRL-\_CTRL-N| to go to Normal mode.
+Use |t_CTRL-\_CTRL-O| to execute one normal mode command and then return
+to terminal mode.
 
 
 You found it, Arthur!				*holy-grail*
diff --git a/runtime/doc/intro.txt b/runtime/doc/intro.txt
index 92ba7b4079..ae80935032 100644
--- a/runtime/doc/intro.txt
+++ b/runtime/doc/intro.txt
@@ -458,7 +458,7 @@ Ex mode			Like Command-line mode, but after entering a command
 Terminal mode		In Terminal mode all input (except CTRL-\) is sent to
 			the process running in the current |terminal| buffer.
 			If CTRL-\ is pressed, the next key is sent unless it
-			is CTRL-N (|CTRL-\_CTRL-N|).
+			is CTRL-N (|CTRL-\_CTRL-N|) or CTRL-O (|t_CTRL-\_CTRL-O|).
 			If the 'showmode' option is on "-- TERMINAL --" is shown
 			at the bottom of the window.
 
@@ -550,7 +550,8 @@ Ex		 :vi	  --	  --	 --	    --	      --
 *6 Go from Select mode to Insert mode by typing a printable character.  The
    selection is deleted and the character is inserted.
 
-	*CTRL-\_CTRL-N* *i_CTRL-\_CTRL-N* *c_CTRL-\_CTRL-N* *v_CTRL-\_CTRL-N*
+			*CTRL-\_CTRL-N* *i_CTRL-\_CTRL-N* *c_CTRL-\_CTRL-N*
+				      *v_CTRL-\_CTRL-N* *t_CTRL-\_CTRL-N*
 Additionally the command CTRL-\ CTRL-N or <C-\><C-N> can be used to go to
 Normal mode from any other mode.  This can be used to make sure Vim is in
 Normal mode, without causing a beep like <Esc> would.  However, this does not
diff --git a/runtime/doc/nvim_terminal_emulator.txt b/runtime/doc/nvim_terminal_emulator.txt
index a7be9ff98f..546f92e92f 100644
--- a/runtime/doc/nvim_terminal_emulator.txt
+++ b/runtime/doc/nvim_terminal_emulator.txt
@@ -47,8 +47,10 @@ Input						*terminal-input*
 
 To send input, enter |Terminal-mode| with |i|, |I|, |a|, |A| or
 |:startinsert|. In this mode all keys except <C-\> are sent to the underlying
-program. If <C-\> is pressed, the next key is sent unless it is <C-N>. Use
-<C-\><C-N> to return to normal-mode. |CTRL-\_CTRL-N|
+program. If <C-\> is pressed, the next key is sent unless it is <C-N> or <C-O>.
+Use <C-\><C-N> to return to normal mode. |CTRL-\_CTRL-N|
+Use <C-\><C-O> to execute one normal mode command and then return to terminal
+mode. *t_CTRL-\_CTRL-O*
 
 Terminal-mode forces these local options:
 
diff --git a/runtime/doc/various.txt b/runtime/doc/various.txt
index 9eb6470962..cae9c76030 100644
--- a/runtime/doc/various.txt
+++ b/runtime/doc/various.txt
@@ -239,7 +239,8 @@ g8			Print the hex values of the bytes used in the
 
 			Type |i| to enter |Terminal-mode|, then keys are sent to
 			the job running in the terminal. Type <C-\><C-N> to
-			leave Terminal-mode. |CTRL-\_CTRL-N|
+			leave Terminal-mode. |CTRL-\_CTRL-N|. Type <C-\><C-O>
+			to execute a single normal mode command |t_CTRL-\_CTRL-O|
 
 			Fails if changes have been made to the current buffer,
 			unless 'hidden' is set.
diff --git a/src/nvim/edit.c b/src/nvim/edit.c
index e7a8f81813..5861e4c52b 100644
--- a/src/nvim/edit.c
+++ b/src/nvim/edit.c
@@ -1223,10 +1223,10 @@ bool edit(int cmdchar, bool startln, long count)
       // the value of `restart_edit` before `ex_normal` returns.
       restart_edit = 'i';
       force_restart_edit = true;
+      return false;
     } else {
-      terminal_enter();
+      return terminal_enter();
     }
-    return false;
   }
 
   // Don't allow inserting in the sandbox.
diff --git a/src/nvim/screen.c b/src/nvim/screen.c
index 80f6f75fea..0d3b936c48 100644
--- a/src/nvim/screen.c
+++ b/src/nvim/screen.c
@@ -6026,7 +6026,11 @@ int showmode(void)
           msg_puts_attr(_(" INSERT"), attr);
         } else if (restart_edit == 'I' || restart_edit == 'i'
                    || restart_edit == 'a' || restart_edit == 'A') {
-          msg_puts_attr(_(" (insert)"), attr);
+          if (curbuf->terminal) {
+            msg_puts_attr(_(" (terminal)"), attr);
+          } else {
+            msg_puts_attr(_(" (insert)"), attr);
+          }
         } else if (restart_edit == 'R') {
           msg_puts_attr(_(" (replace)"), attr);
         } else if (restart_edit == 'V') {
diff --git a/src/nvim/state.c b/src/nvim/state.c
index be8017ea83..d6cca71ad8 100644
--- a/src/nvim/state.c
+++ b/src/nvim/state.c
@@ -211,12 +211,15 @@ void get_mode(char *buf)
       buf[i++] = 'o';
       // to be able to detect force-linewise/blockwise/charwise operations
       buf[i++] = (char)motion_force;
+    } else if (curbuf->terminal) {
+      buf[i++] = 't';
+      if (restart_edit == 'I') {
+        buf[i++] = 'T';
+      }
     } else if (restart_edit == 'I' || restart_edit == 'R'
                || restart_edit == 'V') {
       buf[i++] = 'i';
       buf[i++] = (char)restart_edit;
-    } else if (curbuf->terminal) {
-      buf[i++] = 't';
     }
   }
 
diff --git a/src/nvim/terminal.c b/src/nvim/terminal.c
index fc02d9d53a..c23aff00cb 100644
--- a/src/nvim/terminal.c
+++ b/src/nvim/terminal.c
@@ -82,6 +82,7 @@ typedef struct terminal_state {
   int save_rd;              // saved value of RedrawingDisabled
   bool close;
   bool got_bsl;             // if the last input was <C-\>
+  bool got_bsl_o;           // if left terminal mode with <c-\><c-o>
 } TerminalState;
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
@@ -388,12 +389,11 @@ void terminal_check_size(Terminal *term)
 }
 
 /// Implements MODE_TERMINAL state. :help Terminal-mode
-void terminal_enter(void)
+bool terminal_enter(void)
 {
   buf_T *buf = curbuf;
   assert(buf->terminal);  // Should only be called when curbuf has a terminal.
-  TerminalState state, *s = &state;
-  memset(s, 0, sizeof(TerminalState));
+  TerminalState s[1] = { 0 };
   s->term = buf->terminal;
   stop_insert_mode = false;
 
@@ -443,7 +443,9 @@ void terminal_enter(void)
   s->state.check = terminal_check;
   state_enter(&s->state);
 
-  restart_edit = 0;
+  if (!s->got_bsl_o) {
+    restart_edit = 0;
+  }
   State = save_state;
   RedrawingDisabled = s->save_rd;
   apply_autocmds(EVENT_TERMLEAVE, NULL, NULL, false, curbuf);
@@ -467,7 +469,11 @@ void terminal_enter(void)
   if (curbuf->terminal == s->term && !s->close) {
     terminal_check_cursor();
   }
-  unshowmode(true);
+  if (restart_edit) {
+    showmode();
+  } else {
+    unshowmode(true);
+  }
   ui_busy_stop();
   if (s->close) {
     bool wipe = s->term->buf_handle != 0;
@@ -477,6 +483,8 @@ void terminal_enter(void)
       do_cmdline_cmd("bwipeout!");
     }
   }
+
+  return s->got_bsl_o;
 }
 
 static void terminal_check_cursor(void)
@@ -564,6 +572,14 @@ static int terminal_execute(VimState *state, int key)
     }
     FALLTHROUGH;
 
+  case Ctrl_O:
+    if (s->got_bsl) {
+      s->got_bsl_o = true;
+      restart_edit = 'I';
+      return 0;
+    }
+    FALLTHROUGH;
+
   default:
     if (key == Ctrl_BSL && !s->got_bsl) {
       s->got_bsl = true;
diff --git a/test/functional/terminal/buffer_spec.lua b/test/functional/terminal/buffer_spec.lua
index ec3066c20d..23430a620b 100644
--- a/test/functional/terminal/buffer_spec.lua
+++ b/test/functional/terminal/buffer_spec.lua
@@ -13,6 +13,7 @@ local exc_exec = helpers.exc_exec
 local matches = helpers.matches
 local exec_lua = helpers.exec_lua
 local sleep = helpers.sleep
+local funcs = helpers.funcs
 
 describe(':terminal buffer', function()
   local screen
@@ -300,6 +301,44 @@ describe(':terminal buffer', function()
     feed_command('put a')  -- register a is empty
     helpers.assert_alive()
   end)
+
+  it([[can use temporary normal mode <c-\><c-o>]], function()
+    eq('t', funcs.mode(1))
+    feed [[<c-\><c-o>]]
+    screen:expect{grid=[[
+      tty ready                                         |
+      {2:^ }                                                 |
+                                                        |
+                                                        |
+                                                        |
+                                                        |
+      {3:-- (terminal) --}                                  |
+    ]]}
+    eq('ntT', funcs.mode(1))
+
+    feed [[:let g:x = 17]]
+    screen:expect{grid=[[
+      tty ready                                         |
+      {2: }                                                 |
+                                                        |
+                                                        |
+                                                        |
+                                                        |
+      :let g:x = 17^                                     |
+    ]]}
+
+    feed [[<cr>]]
+    screen:expect{grid=[[
+      tty ready                                         |
+      {1: }                                                 |
+                                                        |
+                                                        |
+                                                        |
+                                                        |
+      {3:-- TERMINAL --}                                    |
+    ]]}
+    eq('t', funcs.mode(1))
+  end)
 end)
 
 describe('No heap-buffer-overflow when using', function()