mruby-bin-mirb: show incrementing line numbers in multi-line prompts

Previously, all continuation lines showed the same line number (e.g.,
"1*" for every line). Now each line shows its actual line number:

  1> class Foo
  2*   def bar
  3*   end
  4* end

Add mirb_editor_set_prompt_format() which accepts printf-style format
strings (e.g., "%d> ", "%d* ") and calculates the correct prompt length
for each line to ensure proper cursor positioning.

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

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

@@ -557,12 +557,9 @@ main(int argc, char **argv)
     if (use_editor && mirb_editor_supported(&editor)) {
       /* Use multi-line editor */
       char *input;
-      char prompt[16], prompt_cont[16];
       mirb_edit_result res;
 
-      snprintf(prompt, sizeof(prompt), "%d> ", line_num);
-      snprintf(prompt_cont, sizeof(prompt_cont), "%d* ", line_num);
-      mirb_editor_set_prompts(&editor, prompt, prompt_cont);
+      mirb_editor_set_prompt_format(&editor, "%d> ", "%d* ", line_num);
 
       res = mirb_editor_read(&editor, &input);
 

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

@@ -202,6 +202,9 @@ mirb_editor_init(mirb_editor *ed)
   ed->prompt_cont = "* ";
   ed->prompt_len = 2;
   ed->prompt_cont_len = 2;
+  ed->prompt_fmt = NULL;
+  ed->prompt_cont_fmt = NULL;
+  ed->line_num_base = 1;
   ed->use_color = FALSE;
   ed->initialized = TRUE;
 
@@ -223,7 +226,7 @@ mirb_editor_cleanup(mirb_editor *ed)
 }
 
 /*
- * Set prompts
+ * Set prompts (fixed strings)
  */
 void
 mirb_editor_set_prompts(mirb_editor *ed, const char *prompt, const char *prompt_cont)
@@ -232,6 +235,23 @@ mirb_editor_set_prompts(mirb_editor *ed, const char *prompt, const char *prompt_
   ed->prompt_cont = prompt_cont;
   ed->prompt_len = strlen(prompt);
   ed->prompt_cont_len = strlen(prompt_cont);
+  ed->prompt_fmt = NULL;
+  ed->prompt_cont_fmt = NULL;
+}
+
+/*
+ * Set prompt format strings for line-numbered prompts
+ */
+void
+mirb_editor_set_prompt_format(mirb_editor *ed, const char *prompt_fmt,
+                               const char *prompt_cont_fmt, int line_num)
+{
+  ed->prompt_fmt = prompt_fmt;
+  ed->prompt_cont_fmt = prompt_cont_fmt;
+  ed->line_num_base = line_num;
+  /* Estimate prompt length (assuming line numbers up to 999) */
+  ed->prompt_len = strlen(prompt_fmt) + 2;  /* %d -> up to 3 digits, minus 2 for %d */
+  ed->prompt_cont_len = strlen(prompt_cont_fmt) + 2;
 }
 
 /*
@@ -262,20 +282,50 @@ mirb_editor_supported(mirb_editor *ed)
   return ed->term.supported;
 }
 
+/*
+ * Calculate prompt length for given line
+ */
+static size_t
+calc_prompt_len(mirb_editor *ed, size_t line_idx)
+{
+  if (ed->prompt_fmt != NULL) {
+    /* Format string: calculate actual length */
+    int line_num = ed->line_num_base + (int)line_idx;
+    const char *fmt = (line_idx == 0) ? ed->prompt_fmt : ed->prompt_cont_fmt;
+    return (size_t)snprintf(NULL, 0, fmt, line_num);
+  }
+  else {
+    /* Fixed prompt string */
+    return (line_idx == 0) ? ed->prompt_len : ed->prompt_cont_len;
+  }
+}
+
 /*
  * Print prompt for given line
  */
 static void
 print_prompt(mirb_editor *ed, size_t line_idx)
 {
-  const char *p = (line_idx == 0) ? ed->prompt : ed->prompt_cont;
+  int line_num = ed->line_num_base + (int)line_idx;
 
   if (ed->use_color) {
-    printf("%s%s%s", COLOR_GREEN, p, COLOR_RESET);
+    printf("%s", COLOR_GREEN);
+  }
+
+  if (ed->prompt_fmt != NULL) {
+    /* Use format string with line number */
+    const char *fmt = (line_idx == 0) ? ed->prompt_fmt : ed->prompt_cont_fmt;
+    printf(fmt, line_num);
   }
   else {
+    /* Use fixed prompt string */
+    const char *p = (line_idx == 0) ? ed->prompt : ed->prompt_cont;
     printf("%s", p);
   }
+
+  if (ed->use_color) {
+    printf("%s", COLOR_RESET);
+  }
 }
 
 /*
@@ -289,7 +339,6 @@ print_prompt(mirb_editor *ed, size_t line_idx)
 static void
 refresh_display(mirb_editor *ed)
 {
-  size_t prompt_len;
   size_t lines_to_go_up;
 
   /* Calculate how many lines up we need to go to reach start of input */
@@ -323,8 +372,8 @@ refresh_display(mirb_editor *ed)
     mirb_term_cursor_up((int)lines_up_from_end);
   }
 
-  /* Position column on cursor line */
-  prompt_len = (ed->buf.cursor_line == 0) ? ed->prompt_len : ed->prompt_cont_len;
+  /* Position column on cursor line (calculate actual prompt length) */
+  size_t prompt_len = calc_prompt_len(ed, ed->buf.cursor_line);
   mirb_term_cursor_col((int)(prompt_len + ed->buf.cursor_col + 1));
 
   /* Update tracking */

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

@@ -42,6 +42,10 @@ typedef struct mirb_editor {
   size_t prompt_len;          /* length of primary prompt */
   size_t prompt_cont_len;     /* length of continuation prompt */
 
+  const char *prompt_fmt;     /* prompt format string (e.g., "%d> ") */
+  const char *prompt_cont_fmt;/* continuation format (e.g., "%d* ") */
+  int line_num_base;          /* starting line number for prompts */
+
   mirb_check_complete_fn *check_complete;  /* completion checker */
   void *check_complete_data;              /* user data for checker */
 
@@ -64,12 +68,22 @@ mrb_bool mirb_editor_init(mirb_editor *ed);
 void mirb_editor_cleanup(mirb_editor *ed);
 
 /*
- * Set prompts
+ * Set prompts (fixed strings)
  */
 void mirb_editor_set_prompts(mirb_editor *ed,
                               const char *prompt,
                               const char *prompt_cont);
 
+/*
+ * Set prompt format strings for line-numbered prompts
+ * Format strings should contain %d for line number (e.g., "%d> ", "%d* ")
+ * line_num is the starting line number
+ */
+void mirb_editor_set_prompt_format(mirb_editor *ed,
+                                    const char *prompt_fmt,
+                                    const char *prompt_cont_fmt,
+                                    int line_num);
+
 /*
  * Set completion checker callback
  */