Add a "back to indentation" key in copy mode to move the cursor to the first

non-whitespace character. ^ with vi and M-m with emacs key bindings. Another
from Kalle Olavi Niemitalo, thanks.

mode-key.c

@@ -105,8 +105,9 @@ mode_key_lookup_vi(struct mode_key_data *mdata, int key)
 			return (MODEKEYCMD_CHOOSE);
 		return (MODEKEYCMD_COPYSELECTION);
 	case '0':
-	case '^':
 		return (MODEKEYCMD_STARTOFLINE);
+	case '^':
+		return (MODEKEYCMD_BACKTOINDENTATION);
 	case '\033':
 		return (MODEKEYCMD_CLEARSELECTION);
 	case 'j':
@@ -160,6 +161,8 @@ mode_key_lookup_emacs(struct mode_key_data *mdata, int key)
 		return (MODEKEYCMD_CHOOSE);
 	case '\001':
 		return (MODEKEYCMD_STARTOFLINE);
+	case KEYC_ADDESC('m'):
+		return (MODEKEYCMD_BACKTOINDENTATION);
 	case '\007':
 		return (MODEKEYCMD_CLEARSELECTION);
 	case '\027':

status.c

@@ -709,6 +709,7 @@ status_prompt_key(struct client *c, int key)
 		}
 		break;
 	case MODEKEYCMD_STARTOFLINE:
+	case MODEKEYCMD_BACKTOINDENTATION:
 		if (c->prompt_index != 0) {
 			c->prompt_index = 0;
 			c->flags |= CLIENT_STATUS;

tmux.1

@@ -306,7 +306,8 @@ option).
 The following keys are supported as appropriate for the mode:
 .Bl -column "FunctionXXXXXXXXXXXX" "viXXXXXX" "emacs" -offset indent
 .It Sy "Function" Ta Sy "vi" Ta Sy "emacs"
-.It Li "Start of line" Ta "0 or ^" Ta "C-a"
+.It Li "Start of line" Ta "0" Ta "C-a"
+.It Li "Back to indentation" Ta "^" Ta "M-m"
 .It Li "Clear selection" Ta "Escape" Ta "C-g"
 .It Li "Copy selection" Ta "Enter" Ta "M-w"
 .It Li "Cursor down" Ta "j" Ta "Down"

tmux.h

@@ -357,6 +357,7 @@ struct msg_resize_data {
 /* Editing keys. */
 enum mode_key_cmd {
 	MODEKEYCMD_BACKSPACE = 0x1000,
+	MODEKEYCMD_BACKTOINDENTATION,
 	MODEKEYCMD_CHOOSE,
 	MODEKEYCMD_CLEARSELECTION,
 	MODEKEYCMD_COMPLETE,

window-copy.c

@@ -50,6 +50,7 @@ int	window_copy_is_space(struct window_pane *, u_int, u_int);
 u_int	window_copy_find_length(struct window_pane *, u_int);
 void	window_copy_set_cursor_x(struct window_pane *, u_int);
 void	window_copy_cursor_start_of_line(struct window_pane *);
+void	window_copy_cursor_back_to_indentation(struct window_pane *);
 void	window_copy_cursor_end_of_line(struct window_pane *);
 void	window_copy_cursor_left(struct window_pane *);
 void	window_copy_cursor_right(struct window_pane *);
@@ -207,6 +208,9 @@ window_copy_key(struct window_pane *wp, struct client *c, int key)
 	case MODEKEYCMD_STARTOFLINE:
 		window_copy_cursor_start_of_line(wp);
 		break;
+	case MODEKEYCMD_BACKTOINDENTATION:
+		window_copy_cursor_back_to_indentation(wp);
+		break;
 	case MODEKEYCMD_ENDOFLINE:
 		window_copy_cursor_end_of_line(wp);
 		break;
@@ -600,6 +604,33 @@ window_copy_cursor_start_of_line(struct window_pane *wp)
 		window_copy_update_cursor(wp);
 }
 
+void
+window_copy_cursor_back_to_indentation(struct window_pane *wp)
+{
+	struct window_copy_mode_data	*data = wp->modedata;
+	u_int				 px, py, xx;
+	const struct grid_cell		*gc;
+
+	px = 0;
+	py = screen_hsize(&wp->base) + data->cy - data->oy;
+	xx = window_copy_find_length(wp, py);
+
+	/*
+	 * Don't use window_copy_is_space because that treats some word
+	 * delimiters as spaces.
+	 */
+	while (px < xx) {
+		gc = grid_peek_cell(wp->base.grid, px, py);
+		if (gc->flags & GRID_FLAG_UTF8)
+			break;
+		if (gc->data != ' ')
+			break;
+		px++;
+	}
+
+	window_copy_set_cursor_x(wp, px);
+}
+
 void
 window_copy_cursor_end_of_line(struct window_pane *wp)
 {