Change vi-mode tilde to toggle character case

This updates the behavior of tilde to match the behavior found in vim.
In vim, tilde toggles the case of the character under the cursor and
advances one character. In visual mode, the case of each selected
character is toggled, the cursor position moves to the beginning of
the selection, and the mode is changed to normal. In fish, tilde
capitalizes the current letter and advances one word. There is no
current tilde command for visual mode in fish.

This patch adds the readline commands `togglecase-letter` and
`togglecase-selection` to match the behavior of vim more closely. The
only difference is that in visual mode, the cursor is not modified.
Modifying the cursor in visual mode would require either moving it in
`togglecase-selection`, which seems outside its scope or adding
something like a `move-to-selection-start` readline command.

share/functions/fish_vi_key_bindings.fish

@@ -187,7 +187,7 @@ function fish_vi_key_bindings --description 'vi-like key bindings for fish'
     bind -s --preset -m insert ci backward-jump-till and repeat-jump-reverse and begin-selection repeat-jump kill-selection end-selection repaint-mode
     bind -s --preset -m insert ca backward-jump and repeat-jump-reverse and begin-selection repeat-jump kill-selection end-selection repaint-mode
 
-    bind -s --preset '~' capitalize-word
+    bind -s --preset '~' togglecase-char forward-char
     bind -s --preset gu downcase-word
     bind -s --preset gU upcase-word
 
@@ -291,6 +291,7 @@ function fish_vi_key_bindings --description 'vi-like key bindings for fish'
     bind -s --preset -M visual -m default X kill-whole-line end-selection repaint-mode
     bind -s --preset -M visual -m default y kill-selection yank end-selection repaint-mode
     bind -s --preset -M visual -m default '"*y' "commandline -s | xsel -p; commandline -f end-selection repaint-mode"
+    bind -s --preset -M visual -m default '~' togglecase-selection end-selection repaint-mode
 
     bind -s --preset -M visual -m default \cc end-selection repaint-mode
     bind -s --preset -M visual -m default \e end-selection repaint-mode

src/input.cpp

@@ -123,6 +123,8 @@ static const input_function_metadata_t input_function_metadata[] = {
     {readline_cmd_t::upcase_word, L"upcase-word"},
     {readline_cmd_t::downcase_word, L"downcase-word"},
     {readline_cmd_t::capitalize_word, L"capitalize-word"},
+    {readline_cmd_t::togglecase_char, L"togglecase-char"},
+    {readline_cmd_t::togglecase_selection, L"togglecase-selection"},
     {readline_cmd_t::execute, L"execute"},
     {readline_cmd_t::beginning_of_buffer, L"beginning-of-buffer"},
     {readline_cmd_t::end_of_buffer, L"end-of-buffer"},

src/input_common.h

@@ -48,6 +48,8 @@ enum class readline_cmd_t {
     upcase_word,
     downcase_word,
     capitalize_word,
+    togglecase_char,
+    togglecase_selection,
     execute,
     beginning_of_buffer,
     end_of_buffer,

src/reader.cpp

@@ -3219,6 +3219,72 @@ void reader_data_t::handle_readline_command(readline_cmd_t c, readline_loop_stat
             }
             break;
         }
+        case rl::togglecase_char: {
+            editable_line_t *el = active_edit_line();
+            size_t buff_pos = el->position();
+
+            // Check that the cursor is on a character
+            if (buff_pos < el->size()) {
+                wchar_t chr = el->text().at(buff_pos);
+                wcstring replacement;
+
+                // Toggle the case of the current character
+                bool make_uppercase = iswlower(chr);
+                if (make_uppercase) {
+                    chr = towupper(chr);
+                } else {
+                    chr = tolower(chr);
+                }
+
+                replacement.push_back(chr);
+                el->replace_substring(buff_pos, (size_t)1, std::move(replacement));
+
+                // Restore the buffer position since replace_substring moves
+                // the buffer position ahead of the replaced text.
+                update_buff_pos(el, buff_pos);
+
+                command_line_changed(el);
+                super_highlight_me_plenty();
+                reader_repaint_needed();
+            }
+            break;
+        }
+        case rl::togglecase_selection: {
+            editable_line_t *el = active_edit_line();
+
+            // Check that we have an active selection and get the bounds.
+            size_t start, len;
+            if (reader_get_selection(&start, &len)) {
+                size_t buff_pos = el->position();
+                wcstring replacement;
+
+                // Loop through the selected characters and toggle their case.
+                for (size_t pos = start; pos < start + len && pos < el->size(); pos++) {
+                    wchar_t chr = el->text().at(pos);
+
+                    // Toggle the case of the current character.
+                    bool make_uppercase = iswlower(chr);
+                    if (make_uppercase) {
+                        chr = towupper(chr);
+                    } else {
+                        chr = tolower(chr);
+                    }
+
+                    replacement.push_back(chr);
+                }
+
+                el->replace_substring(start, len, std::move(replacement));
+
+                // Restore the buffer position since replace_substring moves
+                // the buffer position ahead of the replaced text.
+                update_buff_pos(el, buff_pos);
+
+                command_line_changed(el);
+                super_highlight_me_plenty();
+                reader_repaint_needed();
+            }
+            break;
+        }
         case rl::upcase_word:
         case rl::downcase_word:
         case rl::capitalize_word: {