kconfig: Document automatic submenu creation code

It's tricky to figure out what it does (and how) without staring at the
code for a long time. Document it to make it more transparent.

No functional changes. Only comments added.

Signed-off-by: Ulf Magnusson <ulfalizer@gmail.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>

diff --git a/config/menu.c b/config/menu.c
index 41c79bef3d075fa1122643ceb3cdae9e8289e8d5..d061a4d4e2030e6ea801119c2173f07f1e782bb1 100644 (file)
--- a/config/menu.c
+++ b/config/menu.c
@@ -418,25 +418,63 @@ void menu_finalize(struct menu *parent)
                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);