mruby-bin-mirb: add command history with Up/Down navigation

Add in-memory command history for mirb sessions:
- Up arrow on first line: navigate to older history entries
- Down arrow on last line: navigate to newer history entries
- Current input is preserved when browsing and restored when
  navigating past the newest entry
- History uses a circular buffer (100 entries max)
- Duplicate consecutive entries are not added

Co-authored-by: Claude <noreply@anthropic.com>

mrbgems/mruby-bin-mirb/tools/mirb/mirb.c

@@ -750,6 +750,10 @@ main(int argc, char **argv)
           *(mrb->c->ci->stack + 1) = result;
 #endif
         }
+        /* Add to history after evaluation (success or error) */
+        if (use_editor) {
+          mirb_editor_history_add(&editor, ruby_code);
+        }
       }
       ruby_code[0] = '\0';
       last_code_line[0] = '\0';

mrbgems/mruby-bin-mirb/tools/mirb/mirb_editor.c

@@ -192,6 +192,12 @@ mirb_editor_init(mirb_editor *ed)
     return FALSE;
   }
 
+  if (!mirb_history_init(&ed->hist, MIRB_HISTORY_SIZE)) {
+    mirb_buffer_free(&ed->buf);
+    mirb_term_cleanup(&ed->term);
+    return FALSE;
+  }
+
   ed->prompt = "> ";
   ed->prompt_cont = "* ";
   ed->prompt_len = 2;
@@ -210,6 +216,7 @@ mirb_editor_cleanup(mirb_editor *ed)
 {
   if (!ed->initialized) return;
 
+  mirb_history_free(&ed->hist);
   mirb_buffer_free(&ed->buf);
   mirb_term_cleanup(&ed->term);
   ed->initialized = FALSE;
@@ -336,6 +343,8 @@ handle_key(mirb_editor *ed, int key, mirb_edit_result *result)
 {
   switch (key) {
   case MIRB_KEY_ENTER:
+    /* Stop history browsing */
+    mirb_history_browse_stop(&ed->hist);
     /* Check if input is complete */
     if (ed->check_complete) {
       char *code = mirb_buffer_to_string(&ed->buf);
@@ -392,12 +401,40 @@ handle_key(mirb_editor *ed, int key, mirb_edit_result *result)
 
   case MIRB_KEY_UP:
   case MIRB_KEY_CTRL_P:
-    mirb_buffer_cursor_up(&ed->buf);
+    /* If on first line, navigate history; otherwise move cursor up */
+    if (ed->buf.cursor_line == 0) {
+      /* Start history browsing if not already */
+      if (!ed->hist.browsing) {
+        char *current = mirb_buffer_to_string(&ed->buf);
+        mirb_history_browse_start(&ed->hist, current);
+        free(current);
+      }
+      const char *prev = mirb_history_prev(&ed->hist);
+      if (prev) {
+        mirb_buffer_set_string(&ed->buf, prev);
+        mirb_buffer_cursor_finish(&ed->buf);
+      }
+    }
+    else {
+      mirb_buffer_cursor_up(&ed->buf);
+    }
     return TRUE;
 
   case MIRB_KEY_DOWN:
   case MIRB_KEY_CTRL_N:
-    mirb_buffer_cursor_down(&ed->buf);
+    /* If on last line, navigate history; otherwise move cursor down */
+    if (ed->buf.cursor_line == ed->buf.line_count - 1) {
+      if (ed->hist.browsing) {
+        const char *next = mirb_history_next(&ed->hist);
+        if (next) {
+          mirb_buffer_set_string(&ed->buf, next);
+          mirb_buffer_cursor_finish(&ed->buf);
+        }
+      }
+    }
+    else {
+      mirb_buffer_cursor_down(&ed->buf);
+    }
     return TRUE;
 
   case MIRB_KEY_HOME:
@@ -447,6 +484,8 @@ handle_key(mirb_editor *ed, int key, mirb_edit_result *result)
   default:
     /* Insert printable characters */
     if (key >= 32 && key < 127) {
+      /* Stop history browsing when user types */
+      mirb_history_browse_stop(&ed->hist);
       mirb_buffer_insert_char(&ed->buf, (char)key);
       /* Check for auto-dedent after typing 'end' or '}' */
       if (should_dedent(&ed->buf, (char)key)) {
@@ -605,3 +644,12 @@ mirb_editor_read_simple(mirb_editor *ed, char **out_str)
   *out_str = total;
   return MIRB_EDIT_OK;
 }
+
+/*
+ * Add entry to history
+ */
+void
+mirb_editor_history_add(mirb_editor *ed, const char *entry)
+{
+  mirb_history_add(&ed->hist, entry);
+}

mrbgems/mruby-bin-mirb/tools/mirb/mirb_editor.h

@@ -10,6 +10,7 @@
 #include <mruby.h>
 #include "mirb_term.h"
 #include "mirb_buffer.h"
+#include "mirb_history.h"
 
 /*
  * Editor result codes
@@ -34,6 +35,7 @@ typedef mrb_bool mirb_check_complete_fn(const char *code, void *user_data);
 typedef struct mirb_editor {
   mirb_term term;             /* terminal state */
   mirb_buffer buf;            /* editing buffer */
+  mirb_history hist;          /* command history */
 
   const char *prompt;         /* primary prompt (e.g., "> ") */
   const char *prompt_cont;    /* continuation prompt (e.g., "* ") */
@@ -99,4 +101,10 @@ mirb_edit_result mirb_editor_read(mirb_editor *ed, char **out_str);
  */
 mirb_edit_result mirb_editor_read_simple(mirb_editor *ed, char **out_str);
 
+/*
+ * Add entry to history
+ * Called after successful command execution
+ */
+void mirb_editor_history_add(mirb_editor *ed, const char *entry);
+
 #endif /* MIRB_EDITOR_H */

mrbgems/mruby-bin-mirb/tools/mirb/mirb_history.c

@@ -0,0 +1,180 @@
+/*
+** mirb_history.c - Command history for mirb editor
+**
+** See Copyright Notice in mruby.h
+*/
+
+#include "mirb_history.h"
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+/*
+ * Initialize history
+ */
+mrb_bool
+mirb_history_init(mirb_history *hist, size_t capacity)
+{
+  memset(hist, 0, sizeof(*hist));
+
+  if (capacity == 0) capacity = MIRB_HISTORY_SIZE;
+
+  hist->entries = (char**)calloc(capacity, sizeof(char*));
+  if (hist->entries == NULL) return FALSE;
+
+  hist->capacity = capacity;
+  hist->count = 0;
+  hist->start = 0;
+  hist->pos = 0;
+  hist->saved_input = NULL;
+  hist->browsing = FALSE;
+
+  return TRUE;
+}
+
+/*
+ * Free history resources
+ */
+void
+mirb_history_free(mirb_history *hist)
+{
+  if (hist->entries) {
+    for (size_t i = 0; i < hist->capacity; i++) {
+      free(hist->entries[i]);
+    }
+    free(hist->entries);
+    hist->entries = NULL;
+  }
+  free(hist->saved_input);
+  hist->saved_input = NULL;
+  hist->count = 0;
+  hist->capacity = 0;
+}
+
+/*
+ * Get actual index in circular buffer
+ */
+static size_t
+actual_index(mirb_history *hist, size_t logical_idx)
+{
+  return (hist->start + logical_idx) % hist->capacity;
+}
+
+/*
+ * Add entry to history
+ */
+void
+mirb_history_add(mirb_history *hist, const char *entry)
+{
+  if (entry == NULL || entry[0] == '\0') return;
+
+  /* Don't add if same as last entry */
+  if (hist->count > 0) {
+    size_t last_idx = actual_index(hist, hist->count - 1);
+    if (strcmp(hist->entries[last_idx], entry) == 0) {
+      return;
+    }
+  }
+
+  char *copy = strdup(entry);
+  if (copy == NULL) return;
+
+  if (hist->count < hist->capacity) {
+    /* Still have room */
+    size_t idx = actual_index(hist, hist->count);
+    hist->entries[idx] = copy;
+    hist->count++;
+  }
+  else {
+    /* Buffer is full, overwrite oldest */
+    size_t idx = hist->start;
+    free(hist->entries[idx]);
+    hist->entries[idx] = copy;
+    hist->start = (hist->start + 1) % hist->capacity;
+  }
+
+  /* Reset browsing state */
+  hist->browsing = FALSE;
+  hist->pos = hist->count;
+}
+
+/*
+ * Start browsing history
+ */
+void
+mirb_history_browse_start(mirb_history *hist, const char *current_input)
+{
+  if (hist->browsing) return;
+
+  free(hist->saved_input);
+  hist->saved_input = current_input ? strdup(current_input) : NULL;
+  hist->browsing = TRUE;
+  hist->pos = hist->count;  /* Start past the end (at current input) */
+}
+
+/*
+ * Stop browsing history
+ */
+void
+mirb_history_browse_stop(mirb_history *hist)
+{
+  free(hist->saved_input);
+  hist->saved_input = NULL;
+  hist->browsing = FALSE;
+  hist->pos = hist->count;
+}
+
+/*
+ * Get previous entry (older)
+ */
+const char *
+mirb_history_prev(mirb_history *hist)
+{
+  if (hist->count == 0) return NULL;
+
+  if (!hist->browsing) {
+    /* Should call browse_start first, but handle gracefully */
+    hist->browsing = TRUE;
+    hist->pos = hist->count;
+  }
+
+  if (hist->pos == 0) {
+    /* Already at oldest entry */
+    return NULL;
+  }
+
+  hist->pos--;
+  return hist->entries[actual_index(hist, hist->pos)];
+}
+
+/*
+ * Get next entry (newer)
+ */
+const char *
+mirb_history_next(mirb_history *hist)
+{
+  if (!hist->browsing) return NULL;
+
+  if (hist->pos >= hist->count) {
+    /* Already at current input */
+    return NULL;
+  }
+
+  hist->pos++;
+
+  if (hist->pos >= hist->count) {
+    /* Moved past newest entry, return saved input */
+    return hist->saved_input ? hist->saved_input : "";
+  }
+
+  return hist->entries[actual_index(hist, hist->pos)];
+}
+
+/*
+ * Get current entry count
+ */
+size_t
+mirb_history_count(mirb_history *hist)
+{
+  return hist->count;
+}

mrbgems/mruby-bin-mirb/tools/mirb/mirb_history.h

@@ -0,0 +1,76 @@
+/*
+** mirb_history.h - Command history for mirb editor
+**
+** See Copyright Notice in mruby.h
+*/
+
+#ifndef MIRB_HISTORY_H
+#define MIRB_HISTORY_H
+
+#include <mruby.h>
+#include <stddef.h>
+
+/* Default history size */
+#define MIRB_HISTORY_SIZE 100
+
+/*
+ * History entry
+ */
+typedef struct mirb_history {
+  char **entries;         /* array of history entries */
+  size_t capacity;        /* max number of entries */
+  size_t count;           /* current number of entries */
+  size_t start;           /* index of oldest entry (circular buffer) */
+  size_t pos;             /* current browsing position */
+  char *saved_input;      /* saved current input when browsing */
+  mrb_bool browsing;      /* TRUE if currently browsing history */
+} mirb_history;
+
+/*
+ * Initialize history
+ * Returns TRUE on success
+ */
+mrb_bool mirb_history_init(mirb_history *hist, size_t capacity);
+
+/*
+ * Free history resources
+ */
+void mirb_history_free(mirb_history *hist);
+
+/*
+ * Add entry to history
+ * Empty strings are not added
+ * Duplicate of last entry is not added
+ */
+void mirb_history_add(mirb_history *hist, const char *entry);
+
+/*
+ * Start browsing history
+ * Saves the current input for later restoration
+ */
+void mirb_history_browse_start(mirb_history *hist, const char *current_input);
+
+/*
+ * Stop browsing history
+ */
+void mirb_history_browse_stop(mirb_history *hist);
+
+/*
+ * Get previous entry (older)
+ * Returns NULL if at oldest entry or history is empty
+ */
+const char *mirb_history_prev(mirb_history *hist);
+
+/*
+ * Get next entry (newer)
+ * Returns saved input if moving past newest entry
+ * Returns NULL if not browsing
+ */
+const char *mirb_history_next(mirb_history *hist);
+
+/*
+ * Get current entry count
+ */
+size_t mirb_history_count(mirb_history *hist);
+
+#endif /* MIRB_HISTORY_H */