command and binding for transpose-chars

input.cpp

@@ -113,6 +113,7 @@ static const wchar_t * const name_arr[] =
     L"history-token-search-backward",
     L"history-token-search-forward",
     L"self-insert",
+    L"transpose-chars",
     L"null",
     L"eof",
     L"vi-arg-digit",
@@ -197,6 +198,7 @@ static const wchar_t code_arr[] =
     R_HISTORY_TOKEN_SEARCH_BACKWARD,
     R_HISTORY_TOKEN_SEARCH_FORWARD,
     R_SELF_INSERT,
+    R_TRANSPOSE_CHARS,
     R_NULL,
     R_EOF,
     R_VI_ARG_DIGIT,

input.h

@@ -42,6 +42,7 @@ enum
     R_HISTORY_TOKEN_SEARCH_BACKWARD,
     R_HISTORY_TOKEN_SEARCH_FORWARD,
     R_SELF_INSERT,
+    R_TRANSPOSE_CHARS,
     R_VI_ARG_DIGIT,
     R_VI_DELETE_TO,
     R_EXECUTE,

reader.cpp

@@ -3542,6 +3542,33 @@ const wchar_t *reader_readline(void)
                 break;
             }
 
+            case R_TRANSPOSE_CHARS:
+            {
+                if (data->command_length() < 2) {
+                    break;
+                }
+
+                /* If the cursor is at the end, transpose the last two characters of the line */
+                if (data->buff_pos == data->command_length())
+                {
+                    data->buff_pos--;
+                }
+
+                /*
+                 Drag the character before the cursor forward over the character at the cursor, moving
+                 the cursor forward as well.
+                 */
+                if (data->buff_pos > 0)
+                {
+                    wchar_t tmp = data->command_line[data->buff_pos];
+                    data->command_line[data->buff_pos] = data->command_line[data->buff_pos-1];
+                    data->command_line[data->buff_pos-1] = tmp;
+                    data->buff_pos++;
+                    reader_repaint();
+                }
+                break;
+            }
+
             /* Other, if a normal character, we add it to the command */
             default:
             {

share/functions/fish_default_key_bindings.fish

@@ -67,6 +67,7 @@ function fish_default_key_bindings -d "Default (Emacs-like) key bindings for fis
 	bind \cn history-search-forward
 	bind \cf forward-char
 	bind \cb backward-char
+	bind \ct transpose-chars
 	bind \e\x7f backward-kill-word
 	bind \eb backward-word
 	bind \ef forward-word