kitten choose-files: Add a new binding of Alt+Enter to modify the name of an existing file when choosing a save file name

Fixes #9387

kittens/choose_files/main.go

@@ -479,6 +479,26 @@ func (h *Handler) switch_to_save_file_name_mode() error {
 	if h.state.SearchText() != "" {
 		name = h.state.SearchText()
 	}
+	if name == "" {
+		name = h.current_abspath()
+		if name != "" {
+			if r, err := filepath.Rel(h.state.CurrentDir(), name); err == nil {
+				name = r
+			}
+		}
+	}
+	h.initialize_save_file_name(name)
+	return h.draw_screen()
+}
+
+func (h *Handler) switch_to_save_file_name_mode_based_on_existing() error {
+	name := h.current_abspath()
+	if name == "" {
+		return h.switch_to_save_file_name_mode()
+	}
+	if r, err := filepath.Rel(h.state.CurrentDir(), name); err == nil {
+		name = r
+	}
 	h.initialize_save_file_name(name)
 	return h.draw_screen()
 }
@@ -573,6 +593,12 @@ func (h *Handler) dispatch_action(name, args string) (err error) {
 		} else {
 			return h.switch_to_save_file_name_mode()
 		}
+	case "modifyname":
+		if h.state.mode.CanSelectNonExistent() {
+			return h.switch_to_save_file_name_mode_based_on_existing()
+		} else {
+			h.lp.Beep()
+		}
 	case "toggle":
 		switch args {
 		case "preview":

kittens/choose_files/main.py

@@ -133,6 +133,13 @@ When choosing existing directories, will accept the directory whoose
 contents are being currently displayed as the choice.
 Does not work when selecting files to open rather than to save.
 ''')
+map('Modify file name', 'modifyname alt+enter modifyname', long_text='''
+Modify the name of an existing file and select it for saving.
+Useful when specifying a file or directory name for saving that does not yet exist,
+but is based on an existing file name.
+Does not work when selecting files to open rather than to save.
+''')
+
 
 map('Next result', 'next_result down next 1')
 map('Previous result', 'prev_result up next -1')

kittens/choose_files/save-file.go

@@ -24,6 +24,7 @@ func FilePromptCompleter(getcwd func() string) func(string, string) *cli.Complet
 			return ans
 		}
 	}
+	debugprintln(1111111, getcwd())
 	return func(before_cursor, after_cursor string) (ans *cli.Completions) {
 		defer func() {
 			if r := recover(); r != nil {
@@ -39,6 +40,7 @@ func FilePromptCompleter(getcwd func() string) func(string, string) *cli.Complet
 			prefix = d + utils.IfElse(strings.HasSuffix(d, string(os.PathSeparator)), "", string(os.PathSeparator))
 		}
 		dir := ""
+		debugprintln(2222222, getcwd())
 		if path == "" {
 			path = getcwd()
 			dir = path