system/readline: Add support for line movements and editing

This commit adds support to nsh> command line editing. This is one
of the most missing feature of the NuttShell. If you typed a long
command line and make a mistake you need to press Backspace and
remove everything until reach that typo. Only the basic editing
feature is enabled by default (left/right keys movement, Home/End
to move to the beginning or ending of the command line).

More advanced features are available when CONFIG_READLINE_EDIT_EMACS
is selected. It enables the Emacs-style control keys (Ctrl+A/B/D/E/F/K/U/W)
that allow more flexible line editing.

Other more advanced feature is enabled when CONFIG_READLINE_CMD_HISTORY
and CONFIG_READLINE_EDIT_EMACS_REVERSE_SEARCH are enabled. It allows the
user to press Ctrl+R to do reverse search in the command line history.

Signed-off-by: Alan C. Assis <acassis@gmail.com>
Assisted-by: Claude Code

nshlib/nsh_session.c

@@ -223,6 +223,12 @@ int nsh_session(FAR struct console_stdio_s *pstate,
 
       write(OUTFD(pstate), nsh_prompt(), strlen(nsh_prompt()));
 
+#ifdef CONFIG_READLINE_TABCOMPLETION
+      /* Set the prompt so readline can redraw it for editing features */
+
+      readline_prompt(nsh_prompt());
+#endif
+
       /* readline() normally returns the number of characters read, but
        * will return EOF on end of file or if an error occurs.  EOF
        * will cause the session to terminate.

system/readline/Kconfig

@@ -54,6 +54,25 @@ config READLINE_MAX_EXTCMDS
 
 endif # READLINE_TABCOMPLETION
 
+config READLINE_EDIT
+	bool "Command line editing"
+	default y if !DEFAULT_SMALL
+	---help---
+		Build in support for full command-line editing using cursor keys,
+		Home/End, Delete. Requires a VT100/ANSI-compatible terminal.
+
+if READLINE_EDIT
+
+config READLINE_EDIT_EMACS
+	bool "Emacs-style control keys"
+	default n
+	---help---
+		Enable emacs-style control key bindings:
+		Ctrl+A Home, Ctrl+E End, Ctrl+K kill-to-end,
+		Ctrl+U kill-to-start, Ctrl+Left/Right word movement.
+
+endif # READLINE_EDIT
+
 config READLINE_CMD_HISTORY
 	bool "Command line history"
 	default n
@@ -96,6 +115,17 @@ config READLINE_CMD_HISTORY_LEN
 		will be READLINE_CMD_HISTORY_LINELEN x READLINE_CMD_HISTORY_LEN.
 		Default: 16
 
+config READLINE_EDIT_EMACS_REVERSE_SEARCH
+	bool "Reverse incremental search (Ctrl+R)"
+	default y
+	depends on READLINE_EDIT_EMACS
+	---help---
+		Enable bash-style Ctrl+R reverse incremental search through the
+		command history.  Typing narrows the search to the most recent
+		matching command; Ctrl+R again searches further back; Enter
+		submits the match; Ctrl+G/Ctrl+C cancels back to the line being
+		edited before Ctrl+R was pressed.
+
 endif # READLINE_CMD_HISTORY
 endif # READLINE_ECHO
 endif # SYSTEM_READLINE