lib/mp-readline: Add word-based move/delete EMACS key sequences.

This commit adds backward-word, backward-kill-word, forward-word,
forward-kill-word sequences for the REPL, with bindings to Alt+F, Alt+B,
Alt+D and Alt+Backspace respectively.  It is disabled by default and can be
enabled via MICROPY_REPL_EMACS_WORDS_MOVE.

Further enabling MICROPY_REPL_EMACS_EXTRA_WORDS_MOVE adds extra bindings
for these new sequences: Ctrl+Right, Ctrl+Left and Ctrl+W.

The features are enabled on unix micropython-coverage and micropython-dev.

2 files changed, 87 insertions, 0 deletions

diff --git a/lib/mp-readline/readline.c b/lib/mp-readline/readline.c
index 1500873f6..296c8aa4a 100644
--- a/lib/mp-readline/readline.c
+++ b/lib/mp-readline/readline.c
@@ -99,6 +99,35 @@ typedef struct _readline_t {
 
 STATIC readline_t rl;
 
+#if MICROPY_REPL_EMACS_WORDS_MOVE
+STATIC size_t cursor_count_word(int forward) {
+    const char *line_buf = vstr_str(rl.line);
+    size_t pos = rl.cursor_pos;
+    bool in_word = false;
+
+    for (;;) {
+        // if moving backwards and we've reached 0... break
+        if (!forward && pos == 0) {
+            break;
+        }
+        // or if moving forwards and we've reached to the end of line... break
+        else if (forward && pos == vstr_len(rl.line)) {
+            break;
+        }
+
+        if (unichar_isalnum(line_buf[pos + (forward - 1)])) {
+            in_word = true;
+        } else if (in_word) {
+            break;
+        }
+
+        pos += forward ? forward : -1;
+    }
+
+    return forward ? pos - rl.cursor_pos : rl.cursor_pos - pos;
+}
+#endif
+
 int readline_process_char(int c) {
     size_t last_line_len = rl.line->len;
     int redraw_step_back = 0;
@@ -149,6 +178,10 @@ int readline_process_char(int c) {
             redraw_step_back = rl.cursor_pos - rl.orig_line_len;
             redraw_from_cursor = true;
         #endif
+        #if MICROPY_REPL_EMACS_EXTRA_WORDS_MOVE
+        } else if (c == CHAR_CTRL_W) {
+            goto backward_kill_word;
+        #endif
         } else if (c == '\r') {
             // newline
             mp_hal_stdout_tx_str("\r\n");
@@ -222,9 +255,40 @@ int readline_process_char(int c) {
             case 'O':
                 rl.escape_seq = ESEQ_ESC_O;
                 break;
+            #if MICROPY_REPL_EMACS_WORDS_MOVE
+            case 'b':
+#if MICROPY_REPL_EMACS_EXTRA_WORDS_MOVE
+backward_word:
+#endif
+                redraw_step_back = cursor_count_word(0);
+                rl.escape_seq = ESEQ_NONE;
+                break;
+            case 'f':
+#if MICROPY_REPL_EMACS_EXTRA_WORDS_MOVE
+forward_word:
+#endif
+                redraw_step_forward = cursor_count_word(1);
+                rl.escape_seq = ESEQ_NONE;
+                break;
+            case 'd':
+                vstr_cut_out_bytes(rl.line, rl.cursor_pos, cursor_count_word(1));
+                redraw_from_cursor = true;
+                rl.escape_seq = ESEQ_NONE;
+                break;
+            case 127:
+#if MICROPY_REPL_EMACS_EXTRA_WORDS_MOVE
+backward_kill_word:
+#endif
+                redraw_step_back = cursor_count_word(0);
+                vstr_cut_out_bytes(rl.line, rl.cursor_pos - redraw_step_back, redraw_step_back);
+                redraw_from_cursor = true;
+                rl.escape_seq = ESEQ_NONE;
+                break;
+            #endif
             default:
                 DEBUG_printf("(ESC %d)", c);
                 rl.escape_seq = ESEQ_NONE;
+                break;
         }
     } else if (rl.escape_seq == ESEQ_ESC_BRACKET) {
         if ('0' <= c && c <= '9') {
@@ -312,6 +376,24 @@ delete_key:
             } else {
                 DEBUG_printf("(ESC [ %c %d)", rl.escape_seq_buf[0], c);
             }
+        #if MICROPY_REPL_EMACS_EXTRA_WORDS_MOVE
+        } else if (c == ';' && rl.escape_seq_buf[0] == '1') {
+            // ';' is used to separate parameters. so first parameter was '1',
+            // that's used for sequences like ctrl+left, which we will try to parse.
+            // escape_seq state is reset back to ESEQ_ESC_BRACKET, as if we've just received
+            // the opening bracket, because more parameters are to come.
+            // we don't track the parameters themselves to keep low on logic and code size. that
+            // might be required in the future if more complex sequences are added.
+            rl.escape_seq = ESEQ_ESC_BRACKET;
+            // goto away from the state-machine, as rl.escape_seq will be overridden.
+            goto redraw;
+        } else if (rl.escape_seq_buf[0] == '5' && c == 'C') {
+            // ctrl+right
+            goto forward_word;
+        } else if (rl.escape_seq_buf[0] == '5' && c == 'D') {
+            // ctrl+left
+            goto backward_word;
+        #endif
         } else {
             DEBUG_printf("(ESC [ %c %d)", rl.escape_seq_buf[0], c);
         }
@@ -330,6 +412,10 @@ delete_key:
         rl.escape_seq = ESEQ_NONE;
     }
 
+#if MICROPY_REPL_EMACS_EXTRA_WORDS_MOVE
+redraw:
+#endif
+
     // redraw command prompt, efficiently
     if (redraw_step_back > 0) {
         mp_hal_move_cursor_back(redraw_step_back);
diff --git a/lib/mp-readline/readline.h b/lib/mp-readline/readline.h
index 00aa9622a..a19e1209a 100644
--- a/lib/mp-readline/readline.h
+++ b/lib/mp-readline/readline.h
@@ -36,6 +36,7 @@
 #define CHAR_CTRL_N (14)
 #define CHAR_CTRL_P (16)
 #define CHAR_CTRL_U (21)
+#define CHAR_CTRL_W (23)
 
 void readline_init0(void);
 int readline(vstr_t *line, const char *prompt);