Beispiel #1
0
struct expr *expr_trans_compare(struct expr *e, enum expr_type type, struct symbol *sym)
{
	struct expr *e1, *e2;

	if (!e) {
		e = expr_alloc_symbol(sym);
		if (type == E_UNEQUAL)
			e = expr_alloc_one(E_NOT, e);
		return e;
	}
	switch (e->type) {
	case E_AND:
		e1 = expr_trans_compare(e->left.expr, E_EQUAL, sym);
		e2 = expr_trans_compare(e->right.expr, E_EQUAL, sym);
		if (sym == &symbol_yes)
			e = expr_alloc_two(E_AND, e1, e2);
		if (sym == &symbol_no)
			e = expr_alloc_two(E_OR, e1, e2);
		if (type == E_UNEQUAL)
			e = expr_alloc_one(E_NOT, e);
		return e;
	case E_OR:
		e1 = expr_trans_compare(e->left.expr, E_EQUAL, sym);
		e2 = expr_trans_compare(e->right.expr, E_EQUAL, sym);
		if (sym == &symbol_yes)
			e = expr_alloc_two(E_OR, e1, e2);
		if (sym == &symbol_no)
			e = expr_alloc_two(E_AND, e1, e2);
		if (type == E_UNEQUAL)
			e = expr_alloc_one(E_NOT, e);
		return e;
	case E_NOT:
		return expr_trans_compare(e->left.expr, type == E_EQUAL ? E_UNEQUAL : E_EQUAL, sym);
	case E_UNEQUAL:
	case E_EQUAL:
		if (type == E_EQUAL) {
			if (sym == &symbol_yes)
				return expr_copy(e);
			if (sym == &symbol_mod)
				return expr_alloc_symbol(&symbol_no);
			if (sym == &symbol_no)
				return expr_alloc_one(E_NOT, expr_copy(e));
		} else {
			if (sym == &symbol_yes)
				return expr_alloc_one(E_NOT, expr_copy(e));
			if (sym == &symbol_mod)
				return expr_alloc_symbol(&symbol_yes);
			if (sym == &symbol_no)
				return expr_copy(e);
		}
		break;
	case E_SYMBOL:
		return expr_alloc_comp(type, e->left.sym, sym);
	case E_LIST:
	case E_RANGE:
	case E_NONE:
		/* panic */;
	}
	return NULL;
}
void menu_finalize(struct menu *parent)
{
	struct menu *menu, *last_menu;
	struct symbol *sym;
	struct property *prop;
	struct expr *parentdep, *basedep, *dep, *dep2, **ep;

	sym = parent->sym;
	if (parent->list) {
		if (sym && sym_is_choice(sym)) {
			if (sym->type == S_UNKNOWN) {
				/* find the first choice value to find out choice type */
				current_entry = parent;
				for (menu = parent->list; menu; menu = menu->next) {
					if (menu->sym && menu->sym->type != S_UNKNOWN) {
						menu_set_type(menu->sym->type);
						break;
					}
				}
			}
			if (parent->prompt &&
			    !expr_is_yes(parent->prompt->visible.expr)) {
				parent->visibility = expr_alloc_and (parent->visibility,
								     parent->prompt->visible.expr);
			}
			/* set the type of the remaining choice values */
			for (menu = parent->list; menu; menu = menu->next) {
				current_entry = menu;
				if (menu->sym && menu->sym->type == S_UNKNOWN)
					menu_set_type(sym->type);
			}
			parentdep = expr_alloc_symbol(sym);
		} else if (parent->prompt)
			parentdep = parent->prompt->visible.expr;
		else
			parentdep = parent->dep;

		for (menu = parent->list; menu; menu = menu->next) {
			basedep = expr_transform(menu->dep);
			basedep = expr_alloc_and(expr_copy(parentdep), basedep);
			basedep = expr_eliminate_dups(basedep);
			menu->dep = basedep;
			if (menu->sym)
				prop = menu->sym->prop;
			else
				prop = menu->prompt;
			for (; prop; prop = prop->next) {
				if (prop->menu != menu)
					continue;
				dep = expr_transform(prop->visible.expr);
				dep = expr_alloc_and(expr_copy(basedep), dep);
				dep = expr_eliminate_dups(dep);
				if (menu->sym && menu->sym->type != S_TRISTATE)
					dep = expr_trans_bool(dep);
				prop->visible.expr = dep;
				if (prop->type == P_SELECT) {
					struct symbol *es = prop_get_symbol(prop);
					es->rev_dep.expr = expr_alloc_or(es->rev_dep.expr,
							expr_alloc_and(expr_alloc_symbol(menu->sym), expr_copy(dep)));
				}
			}
		}
		for (menu = parent->list; menu; menu = menu->next)
			menu_finalize(menu);
	} else if (sym) {
		basedep = parent->prompt ? parent->prompt->visible.expr : NULL;
		basedep = expr_trans_compare(basedep, E_UNEQUAL, &symbol_no);
		basedep = expr_eliminate_dups(expr_transform(basedep));
		last_menu = NULL;
		for (menu = parent->next; menu; menu = menu->next) {
			dep = menu->prompt ? menu->prompt->visible.expr : menu->dep;
			if (!expr_contains_symbol(dep, sym))
				break;
			if (expr_depends_symbol(dep, sym))
				goto next;
			dep = expr_trans_compare(dep, E_UNEQUAL, &symbol_no);
			dep = expr_eliminate_dups(expr_transform(dep));
			dep2 = expr_copy(basedep);
			expr_eliminate_eq(&dep, &dep2);
			expr_free(dep);
			if (!expr_is_yes(dep2)) {
				expr_free(dep2);
				break;
			}
			expr_free(dep2);
		next:
			menu_finalize(menu);
			menu->parent = parent;
			last_menu = menu;
		}
		if (last_menu) {
			parent->list = parent->next;
			parent->next = last_menu->next;
			last_menu->next = NULL;
		}

		sym->dir_dep.expr = expr_alloc_or(sym->dir_dep.expr, parent->dep);
	}
	for (menu = parent->list; menu; menu = menu->next) {
		if (sym && sym_is_choice(sym) &&
		    menu->sym && !sym_is_choice_value(menu->sym)) {
			current_entry = menu;
			menu->sym->flags |= SYMBOL_CHOICEVAL;
			if (!menu->prompt)
				menu_warn(menu, "choice value must have a prompt");
			for (prop = menu->sym->prop; prop; prop = prop->next) {
				if (prop->type == P_DEFAULT)
					prop_warn(prop, "defaults for choice "
						  "values not supported");
				if (prop->menu == menu)
					continue;
				if (prop->type == P_PROMPT &&
				    prop->menu->parent->sym != sym)
					prop_warn(prop, "choice value used outside its choice group");
			}
			/* Non-tristate choice values of tristate choices must
			 * depend on the choice being set to Y. The choice
			 * values' dependencies were propagated to their
			 * properties above, so the change here must be re-
			 * propagated.
			 */
			if (sym->type == S_TRISTATE && menu->sym->type != S_TRISTATE) {
				basedep = expr_alloc_comp(E_EQUAL, sym, &symbol_yes);
				menu->dep = expr_alloc_and(basedep, menu->dep);
				for (prop = menu->sym->prop; prop; prop = prop->next) {
					if (prop->menu != menu)
						continue;
					prop->visible.expr = expr_alloc_and(expr_copy(basedep),
									    prop->visible.expr);
				}
			}
			menu_add_symbol(P_CHOICE, sym, NULL);
			prop = sym_get_choice_prop(sym);
			for (ep = &prop->expr; *ep; ep = &(*ep)->left.expr)
				;
			*ep = expr_alloc_one(E_LIST, NULL);
			(*ep)->right.sym = menu->sym;
		}
		if (menu->list && (!menu->prompt || !menu->prompt->text)) {
			for (last_menu = menu->list; ; last_menu = last_menu->next) {
				last_menu->parent = parent;
				if (!last_menu->next)
					break;
			}
			last_menu->next = menu->next;
			menu->next = menu->list;
			menu->list = NULL;
		}
	}

	if (sym && !(sym->flags & SYMBOL_WARNED)) {
		if (sym->type == S_UNKNOWN)
			menu_warn(parent, "config symbol defined without type");

		if (sym_is_choice(sym) && !parent->prompt)
			menu_warn(parent, "choice must have a prompt");

		/* Check properties connected to this symbol */
		sym_check_prop(sym);
		sym->flags |= SYMBOL_WARNED;
	}

	if (sym && !sym_is_optional(sym) && parent->prompt) {
		sym->rev_dep.expr = expr_alloc_or(sym->rev_dep.expr,
				expr_alloc_and(parent->prompt->visible.expr,
					expr_alloc_symbol(&symbol_mod)));
	}
}
Beispiel #3
0
/*
 * e1 || e2 -> ?
 */
struct expr *
expr_join_or(struct expr *e1, struct expr *e2)
{
    struct expr *tmp;
    struct symbol *sym1, *sym2;

    if (expr_eq(e1, e2))
	return expr_copy(e1);
    if (e1->type != E_EQUAL && e1->type != E_UNEQUAL && e1->type != E_SYMBOL
	&& e1->type != E_NOT)
	return NULL;
    if (e2->type != E_EQUAL && e2->type != E_UNEQUAL && e2->type != E_SYMBOL
	&& e2->type != E_NOT)
	return NULL;
    if (e1->type == E_NOT) {
	tmp = e1->left.expr;
	if (tmp->type != E_EQUAL && tmp->type != E_UNEQUAL
	    && tmp->type != E_SYMBOL)
	    return NULL;
	sym1 = tmp->left.sym;
    } else
	sym1 = e1->left.sym;
    if (e2->type == E_NOT) {
	if (e2->left.expr->type != E_SYMBOL)
	    return NULL;
	sym2 = e2->left.expr->left.sym;
    } else
	sym2 = e2->left.sym;
    if (sym1 != sym2)
	return NULL;
    if (sym1->type != S_BOOLEAN && sym1->type != S_TRISTATE)
	return NULL;
    if (sym1->type == S_TRISTATE) {
	if (e1->type == E_EQUAL && e2->type == E_EQUAL &&
	    ((e1->right.sym == &symbol_yes && e2->right.sym == &symbol_mod) ||
	     (e1->right.sym == &symbol_mod
	      && e2->right.sym == &symbol_yes))) {
	    // (a='y') || (a='m') -> (a!='n')
	    return expr_alloc_comp(E_UNEQUAL, sym1, &symbol_no);
	}
	if (e1->type == E_EQUAL && e2->type == E_EQUAL &&
	    ((e1->right.sym == &symbol_yes && e2->right.sym == &symbol_no) ||
	     (e1->right.sym == &symbol_no && e2->right.sym == &symbol_yes))) {
	    // (a='y') || (a='n') -> (a!='m')
	    return expr_alloc_comp(E_UNEQUAL, sym1, &symbol_mod);
	}
	if (e1->type == E_EQUAL && e2->type == E_EQUAL &&
	    ((e1->right.sym == &symbol_mod && e2->right.sym == &symbol_no) ||
	     (e1->right.sym == &symbol_no && e2->right.sym == &symbol_mod))) {
	    // (a='m') || (a='n') -> (a!='y')
	    return expr_alloc_comp(E_UNEQUAL, sym1, &symbol_yes);
	}
    }
    if (sym1->type == S_BOOLEAN && sym1 == sym2) {
	if ((e1->type == E_NOT && e1->left.expr->type == E_SYMBOL
	     && e2->type == E_SYMBOL) || (e2->type == E_NOT
					  && e2->left.expr->type == E_SYMBOL
					  && e1->type == E_SYMBOL))
	    return expr_alloc_symbol(&symbol_yes);
    }

    printf("optimize ");
    print_expr(0, e1, 0);
    printf(" || ");
    print_expr(0, e2, 0);
    printf(" ?\n");
    return NULL;
}
Beispiel #4
0
static struct expr *expr_join_and(struct expr *e1, struct expr *e2)
{
	struct expr *tmp;
	struct symbol *sym1, *sym2;

	if (expr_eq(e1, e2))
		return expr_copy(e1);
	if (e1->type != E_EQUAL && e1->type != E_UNEQUAL && e1->type != E_SYMBOL && e1->type != E_NOT)
		return NULL;
	if (e2->type != E_EQUAL && e2->type != E_UNEQUAL && e2->type != E_SYMBOL && e2->type != E_NOT)
		return NULL;
	if (e1->type == E_NOT) {
		tmp = e1->left.expr;
		if (tmp->type != E_EQUAL && tmp->type != E_UNEQUAL && tmp->type != E_SYMBOL)
			return NULL;
		sym1 = tmp->left.sym;
	} else
		sym1 = e1->left.sym;
	if (e2->type == E_NOT) {
		if (e2->left.expr->type != E_SYMBOL)
			return NULL;
		sym2 = e2->left.expr->left.sym;
	} else
		sym2 = e2->left.sym;
	if (sym1 != sym2)
		return NULL;
	if (sym1->type != S_BOOLEAN && sym1->type != S_TRISTATE)
		return NULL;

	if ((e1->type == E_SYMBOL && e2->type == E_EQUAL && e2->right.sym == &symbol_yes) ||
	    (e2->type == E_SYMBOL && e1->type == E_EQUAL && e1->right.sym == &symbol_yes))
		// (a) && (a='y') -> (a='y')
		return expr_alloc_comp(E_EQUAL, sym1, &symbol_yes);

	if ((e1->type == E_SYMBOL && e2->type == E_UNEQUAL && e2->right.sym == &symbol_no) ||
	    (e2->type == E_SYMBOL && e1->type == E_UNEQUAL && e1->right.sym == &symbol_no))
		// (a) && (a!='n') -> (a)
		return expr_alloc_symbol(sym1);

	if ((e1->type == E_SYMBOL && e2->type == E_UNEQUAL && e2->right.sym == &symbol_mod) ||
	    (e2->type == E_SYMBOL && e1->type == E_UNEQUAL && e1->right.sym == &symbol_mod))
		// (a) && (a!='m') -> (a='y')
		return expr_alloc_comp(E_EQUAL, sym1, &symbol_yes);

	if (sym1->type == S_TRISTATE) {
		if (e1->type == E_EQUAL && e2->type == E_UNEQUAL) {
			// (a='b') && (a!='c') -> 'b'='c' ? 'n' : a='b'
			sym2 = e1->right.sym;
			if ((e2->right.sym->flags & SYMBOL_CONST) && (sym2->flags & SYMBOL_CONST))
				return sym2 != e2->right.sym ? expr_alloc_comp(E_EQUAL, sym1, sym2)
							     : expr_alloc_symbol(&symbol_no);
		}
		if (e1->type == E_UNEQUAL && e2->type == E_EQUAL) {
			// (a='b') && (a!='c') -> 'b'='c' ? 'n' : a='b'
			sym2 = e2->right.sym;
			if ((e1->right.sym->flags & SYMBOL_CONST) && (sym2->flags & SYMBOL_CONST))
				return sym2 != e1->right.sym ? expr_alloc_comp(E_EQUAL, sym1, sym2)
							     : expr_alloc_symbol(&symbol_no);
		}
		if (e1->type == E_UNEQUAL && e2->type == E_UNEQUAL &&
			   ((e1->right.sym == &symbol_yes && e2->right.sym == &symbol_no) ||
			    (e1->right.sym == &symbol_no && e2->right.sym == &symbol_yes)))
			// (a!='y') && (a!='n') -> (a='m')
			return expr_alloc_comp(E_EQUAL, sym1, &symbol_mod);

		if (e1->type == E_UNEQUAL && e2->type == E_UNEQUAL &&
			   ((e1->right.sym == &symbol_yes && e2->right.sym == &symbol_mod) ||
			    (e1->right.sym == &symbol_mod && e2->right.sym == &symbol_yes)))
			// (a!='y') && (a!='m') -> (a='n')
			return expr_alloc_comp(E_EQUAL, sym1, &symbol_no);

		if (e1->type == E_UNEQUAL && e2->type == E_UNEQUAL &&
			   ((e1->right.sym == &symbol_mod && e2->right.sym == &symbol_no) ||
			    (e1->right.sym == &symbol_no && e2->right.sym == &symbol_mod)))
			// (a!='m') && (a!='n') -> (a='m')
			return expr_alloc_comp(E_EQUAL, sym1, &symbol_yes);

		if ((e1->type == E_SYMBOL && e2->type == E_EQUAL && e2->right.sym == &symbol_mod) ||
		    (e2->type == E_SYMBOL && e1->type == E_EQUAL && e1->right.sym == &symbol_mod) ||
		    (e1->type == E_SYMBOL && e2->type == E_UNEQUAL && e2->right.sym == &symbol_yes) ||
		    (e2->type == E_SYMBOL && e1->type == E_UNEQUAL && e1->right.sym == &symbol_yes))
			return NULL;
	}

	if (DEBUG_EXPR) {
		printf("optimize (");
		expr_fprint(e1, stdout);
		printf(") && (");
		expr_fprint(e2, stdout);
		printf(")?\n");
	}
	return NULL;
}
Beispiel #5
0
void menu_finalize(struct menu *parent)
{
	struct menu *menu, *last_menu;
	struct symbol *sym;
	struct property *prop;
	struct expr *parentdep, *basedep, *dep, *dep2, **ep;

	sym = parent->sym;
	if (parent->list) {
		/*
		 * This menu node has children. We (recursively) process them
		 * and propagate parent dependencies before moving on.
		 */

		if (sym && sym_is_choice(sym)) {
			if (sym->type == S_UNKNOWN) {
				/* find the first choice value to find out choice type */
				current_entry = parent;
				for (menu = parent->list; menu; menu = menu->next) {
					if (menu->sym && menu->sym->type != S_UNKNOWN) {
						menu_set_type(menu->sym->type);
						break;
					}
				}
			}
			/* set the type of the remaining choice values */
			for (menu = parent->list; menu; menu = menu->next) {
				current_entry = menu;
				if (menu->sym && menu->sym->type == S_UNKNOWN)
					menu_set_type(sym->type);
			}

			/*
			 * Use the choice itself as the parent dependency of
			 * the contained items. This turns the mode of the
			 * choice into an upper bound on the visibility of the
			 * choice value symbols.
			 */
			parentdep = expr_alloc_symbol(sym);
		} else if (parent->prompt)
			/* Menu node for 'menu' */
			parentdep = parent->prompt->visible.expr;
		else
			/* Menu node for 'if' */
			parentdep = parent->dep;

		/* For each child menu node... */
		for (menu = parent->list; menu; menu = menu->next) {
			/*
			 * Propagate parent dependencies to the child menu
			 * node, also rewriting and simplifying expressions
			 */
			basedep = rewrite_m(menu->dep);
			basedep = expr_transform(basedep);
			basedep = expr_alloc_and(expr_copy(parentdep), basedep);
			basedep = expr_eliminate_dups(basedep);
			menu->dep = basedep;

			if (menu->sym)
				/*
				 * Note: For symbols, all prompts are included
				 * too in the symbol's own property list
				 */
				prop = menu->sym->prop;
			else
				/*
				 * For non-symbol menu nodes, we just need to
				 * handle the prompt
				 */
				prop = menu->prompt;

			/* For each property... */
			for (; prop; prop = prop->next) {
				if (prop->menu != menu)
					/*
					 * Two possibilities:
					 *
					 * 1. The property lacks dependencies
					 *    and so isn't location-specific,
					 *    e.g. an 'option'
					 *
					 * 2. The property belongs to a symbol
					 *    defined in multiple locations and
					 *    is from some other location. It
					 *    will be handled there in that
					 *    case.
					 *
					 * Skip the property.
					 */
					continue;

				/*
				 * Propagate parent dependencies to the
				 * property's condition, rewriting and
				 * simplifying expressions at the same time
				 */
				dep = rewrite_m(prop->visible.expr);
				dep = expr_transform(dep);
				dep = expr_alloc_and(expr_copy(basedep), dep);
				dep = expr_eliminate_dups(dep);
				if (menu->sym && menu->sym->type != S_TRISTATE)
					dep = expr_trans_bool(dep);
				prop->visible.expr = dep;

				/*
				 * Handle selects and implies, which modify the
				 * dependencies of the selected/implied symbol
				 */
				if (prop->type == P_SELECT) {
					struct symbol *es = prop_get_symbol(prop);
					es->rev_dep.expr = expr_alloc_or(es->rev_dep.expr,
							expr_alloc_and(expr_alloc_symbol(menu->sym), expr_copy(dep)));
				} else if (prop->type == P_IMPLY) {
					struct symbol *es = prop_get_symbol(prop);
					es->implied.expr = expr_alloc_or(es->implied.expr,
							expr_alloc_and(expr_alloc_symbol(menu->sym), expr_copy(dep)));
				}
			}
		}

		if (sym && sym_is_choice(sym))
			expr_free(parentdep);

		/*
		 * Recursively process children in the same fashion before
		 * moving on
		 */
		for (menu = parent->list; menu; menu = menu->next)
			menu_finalize(menu);
	} else if (sym) {
		/*
		 * Automatic submenu creation. If sym is a symbol and A, B, C,
		 * ... are consecutive items (symbols, menus, ifs, etc.) that
		 * all depend on sym, then the following menu structure is
		 * created:
		 *
		 *	sym
		 *	 +-A
		 *	 +-B
		 *	 +-C
		 *	 ...
		 *
		 * This also works recursively, giving the following structure
		 * if A is a symbol and B depends on A:
		 *
		 *	sym
		 *	 +-A
		 *	 | +-B
		 *	 +-C
		 *	 ...
		 */

		basedep = parent->prompt ? parent->prompt->visible.expr : NULL;
		basedep = expr_trans_compare(basedep, E_UNEQUAL, &symbol_no);
		basedep = expr_eliminate_dups(expr_transform(basedep));

		/* Examine consecutive elements after sym */
		last_menu = NULL;
		for (menu = parent->next; menu; menu = menu->next) {
			dep = menu->prompt ? menu->prompt->visible.expr : menu->dep;
			if (!expr_contains_symbol(dep, sym))
				/* No dependency, quit */
				break;
			if (expr_depends_symbol(dep, sym))
				/* Absolute dependency, put in submenu */
				goto next;

			/*
			 * Also consider it a dependency on sym if our
			 * dependencies contain sym and are a "superset" of
			 * sym's dependencies, e.g. '(sym || Q) && R' when sym
			 * depends on R.
			 *
			 * Note that 'R' might be from an enclosing menu or if,
			 * making this a more common case than it might seem.
			 */
			dep = expr_trans_compare(dep, E_UNEQUAL, &symbol_no);
			dep = expr_eliminate_dups(expr_transform(dep));
			dep2 = expr_copy(basedep);
			expr_eliminate_eq(&dep, &dep2);
			expr_free(dep);
			if (!expr_is_yes(dep2)) {
				/* Not superset, quit */
				expr_free(dep2);
				break;
			}
			/* Superset, put in submenu */
			expr_free(dep2);
		next:
			menu_finalize(menu);
			menu->parent = parent;
			last_menu = menu;
		}
		expr_free(basedep);
		if (last_menu) {
			parent->list = parent->next;
			parent->next = last_menu->next;
			last_menu->next = NULL;
		}

		sym->dir_dep.expr = expr_alloc_or(sym->dir_dep.expr, parent->dep);
	}
	for (menu = parent->list; menu; menu = menu->next) {
		if (sym && sym_is_choice(sym) &&
		    menu->sym && !sym_is_choice_value(menu->sym)) {
			current_entry = menu;
			menu->sym->flags |= SYMBOL_CHOICEVAL;
			if (!menu->prompt)
				menu_warn(menu, "choice value must have a prompt");
			for (prop = menu->sym->prop; prop; prop = prop->next) {
				if (prop->type == P_DEFAULT)
					prop_warn(prop, "defaults for choice "
						  "values not supported");
				if (prop->menu == menu)
					continue;
				if (prop->type == P_PROMPT &&
				    prop->menu->parent->sym != sym)
					prop_warn(prop, "choice value used outside its choice group");
			}
			/* Non-tristate choice values of tristate choices must
			 * depend on the choice being set to Y. The choice
			 * values' dependencies were propagated to their
			 * properties above, so the change here must be re-
			 * propagated.
			 */
			if (sym->type == S_TRISTATE && menu->sym->type != S_TRISTATE) {
				basedep = expr_alloc_comp(E_EQUAL, sym, &symbol_yes);
				menu->dep = expr_alloc_and(basedep, menu->dep);
				for (prop = menu->sym->prop; prop; prop = prop->next) {
					if (prop->menu != menu)
						continue;
					prop->visible.expr = expr_alloc_and(expr_copy(basedep),
									    prop->visible.expr);
				}
			}
			menu_add_symbol(P_CHOICE, sym, NULL);
			prop = sym_get_choice_prop(sym);
			for (ep = &prop->expr; *ep; ep = &(*ep)->left.expr)
				;
			*ep = expr_alloc_one(E_LIST, NULL);
			(*ep)->right.sym = menu->sym;
		}

		/*
		 * This code serves two purposes:
		 *
		 * (1) Flattening 'if' blocks, which do not specify a submenu
		 *     and only add dependencies.
		 *
		 *     (Automatic submenu creation might still create a submenu
		 *     from an 'if' before this code runs.)
		 *
		 * (2) "Undoing" any automatic submenus created earlier below
		 *     promptless symbols.
		 *
		 * Before:
		 *
		 *	A
		 *	if ... (or promptless symbol)
		 *	 +-B
		 *	 +-C
		 *	D
		 *
		 * After:
		 *
		 *	A
		 *	if ... (or promptless symbol)
		 *	B
		 *	C
		 *	D
		 */
		if (menu->list && (!menu->prompt || !menu->prompt->text)) {
			for (last_menu = menu->list; ; last_menu = last_menu->next) {
				last_menu->parent = parent;
				if (!last_menu->next)
					break;
			}
			last_menu->next = menu->next;
			menu->next = menu->list;
			menu->list = NULL;
		}
	}

	if (sym && !(sym->flags & SYMBOL_WARNED)) {
		if (sym->type == S_UNKNOWN)
			menu_warn(parent, "config symbol defined without type");

		if (sym_is_choice(sym) && !parent->prompt)
			menu_warn(parent, "choice must have a prompt");

		/* Check properties connected to this symbol */
		sym_check_prop(sym);
		sym->flags |= SYMBOL_WARNED;
	}

	/*
	 * For non-optional choices, add a reverse dependency (corresponding to
	 * a select) of '<visibility> && m'. This prevents the user from
	 * setting the choice mode to 'n' when the choice is visible.
	 *
	 * This would also work for non-choice symbols, but only non-optional
	 * choices clear SYMBOL_OPTIONAL as of writing. Choices are implemented
	 * as a type of symbol.
	 */
	if (sym && !sym_is_optional(sym) && parent->prompt) {
		sym->rev_dep.expr = expr_alloc_or(sym->rev_dep.expr,
				expr_alloc_and(parent->prompt->visible.expr,
					expr_alloc_symbol(&symbol_mod)));
	}
}