kconfig: remove 'optional' property support

The 'choice' statement is primarily used to exclusively select one
option, but the 'optional' property allows all entries to be disabled.

In the following example, both A and B can be disabled simultaneously:

    choice
            prompt "choose A, B, or nothing"
            optional

    config A
            bool "A"

    config B
            bool "B"

    endchoice

You can achieve the equivalent outcome by other means.

A common solution is to add another option to guard the choice block.
In the following example, you can set ENABLE_A_B_CHOICE=n to disable
the entire choice block:

    choice
            prompt "choose A or B"
            depends on ENABLE_A_B_CHOICE

    config A
            bool "A"

    config B
            bool "B"

    endchoice

Another approach is to insert one more entry:

    choice
            prompt "choose A, B, or disable both"

    config A
            bool "A"

    config B
            bool "B"

    config DISABLE_A_AND_B
            bool "choose this to disable both A and B"

    endchoice

Some real examples are DEBUG_INFO_NONE, INITRAMFS_COMPRESSION_NONE,
LTO_NONE, etc.

The 'optional' property is even more unnecessary for a tristate choice.

Without the 'optional' property, you can disable A and B; you can set
'm' in the choice prompt, and disable A and B individually:

    choice
            prompt "choose one built-in or make them modular"

    config A
            tristate "A"

    config B
            tristate "B"

    endchoice

In conclusion, the 'optional' property was unneeded.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <n.schier@avm.de>

1 files changed, 4 insertions, 8 deletions

diff --git a/scripts/kconfig/menu.c b/scripts/kconfig/menu.c
index fe6af8700622..e01b9ee87c05 100644
--- a/scripts/kconfig/menu.c
+++ b/scripts/kconfig/menu.c
@@ -593,15 +593,11 @@ static void _menu_finalize(struct menu *parent, bool inside_choice)
 	}
 
 	/*
-	 * 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.
+	 * For 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.
 	 */
-	if (sym && !sym_is_optional(sym) && parent->prompt) {
+	if (sym && sym_is_choice(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)));