rcfile: when a vital function is not mapped, mention in which menu

Add the reverse of the name-to-menu function to accomplish this.

This fixes https://savannah.gnu.org/bugs/?54449.

src/global.c

@@ -1710,6 +1710,18 @@ int strtomenu(const char *input)
 
 	return -1;
 }
+
+/* Return the name that corresponds to the given menu symbol. */
+char *menu_to_name(int menu)
+{
+	int index = -1;
+
+	while (++index < NUMBER_OF_MENUS)
+		if (menusymbols[index] == menu)
+			return menunames[index];
+
+	return "boooo";
+}
 #endif /* ENABLE_NANORC */
 
 

src/proto.h

@@ -330,6 +330,7 @@ const subnfunc *sctofunc(const sc *s);
 const char *flagtostr(int flag);
 sc *strtosc(const char *input);
 int strtomenu(const char *input);
+char *menu_to_name(int menu);
 #ifdef DEBUG
 void thanks_for_all_the_fish(void);
 #endif

src/rcfile.c

@@ -882,7 +882,8 @@ static void check_vitals_mapped(void)
 				const sc *s = first_sc_for(inmenus[v], f->func);
 				if (!s) {
 					fprintf(stderr, _("No key is bound to function '%s' in "
-										"some menu.  Exiting.\n"), f->desc);
+										"menu '%s'.  Exiting.\n"), f->desc,
+										menu_to_name(inmenus[v]));
 					fprintf(stderr, _("If needed, use nano with the -I option "
 										"to adjust your nanorc settings.\n"));
 					exit(1);