implement swap-selection-start-stop function

The swap-selection-start-stop function goes to the other end of the highlighted text, the equivalent of `o' for vim visual mode.

Add binding to the swap-selection-start-stop function, `o' when in visual
mode.

Document swap-selection-start-stop, begin-selection, end-selection, kill-selection.

doc_src/bind.txt

@@ -75,6 +75,8 @@ The following special input functions are available:
 
 - `beginning-of-line`, move to the beginning of the line
 
+- `begin-selection`, start selecting text
+
 - `capitalize-word`, make the current word begin with a capital letter
 
 - `complete`, guess the remainder of the current token
@@ -93,6 +95,8 @@ The following special input functions are available:
 
 - `end-of-line`, move to the end of the line
 
+- `end-selection`, end selecting text
+
 - `explain`, print a description of possible problems with the current command
 
 - `forward-bigword`, move one whitespace-delimited word to the right
@@ -109,12 +113,16 @@ The following special input functions are available:
 
 - `kill-line`, move everything from the cursor to the end of the line to the killring
 
+- `kill-selection`, move the selected text to the killring
+
 - `kill-whole-line`, move the line to the killring
 
 - `kill-word`, move the next word to the killring
 
 - `suppress-autosuggestion`, remove the current autosuggestion
 
+- `swap-selection-start-stop`, go to the other end of the highlighted text without changing the selection
+
 - `transpose-chars`,  transpose two characters to the left of the cursor
 
 - `transpose-words`, transpose two words to the left of the cursor

share/functions/fish_vi_key_bindings.fish

@@ -200,6 +200,7 @@ function fish_vi_key_bindings --description 'vi-like key bindings for fish'
   bind -M visual W forward-bigword
   bind -M visual e forward-word
   bind -M visual E forward-bigword
+  bind -M visual o swap-selection-start-stop force-repaint
 
   for key in $eol_keys
       bind -M visual $key end-of-line

src/input.cpp

@@ -132,6 +132,7 @@ static const wchar_t * const name_arr[] =
     L"suppress-autosuggestion",
     L"accept-autosuggestion",
     L"begin-selection",
+    L"swap-selection-start-stop",
     L"end-selection",
     L"kill-selection",
     L"forward-jump",
@@ -242,6 +243,7 @@ static const wchar_t code_arr[] =
     R_SUPPRESS_AUTOSUGGESTION,
     R_ACCEPT_AUTOSUGGESTION,
     R_BEGIN_SELECTION,
+    R_SWAP_SELECTION_START_STOP,
     R_END_SELECTION,
     R_KILL_SELECTION,
     R_FORWARD_JUMP,

src/input_common.h

@@ -68,6 +68,7 @@ enum
     R_SUPPRESS_AUTOSUGGESTION,
     R_ACCEPT_AUTOSUGGESTION,
     R_BEGIN_SELECTION,
+    R_SWAP_SELECTION_START_STOP,
     R_END_SELECTION,
     R_KILL_SELECTION,
     R_FORWARD_JUMP,

src/reader.cpp

@@ -4026,6 +4026,17 @@ const wchar_t *reader_readline(int nchars)
                 break;
             }
 
+            case R_SWAP_SELECTION_START_STOP:
+            {
+                if (!data->sel_active) break;
+                size_t tmp = data->sel_begin_pos;
+                data->sel_begin_pos = data->command_line.position;
+                data->sel_start_pos = data->command_line.position;
+                editable_line_t *el = data->active_edit_line();
+                update_buff_pos(el, tmp);
+                break;
+            }
+
             case R_END_SELECTION:
             {
                 data->sel_active = false;