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, 1 insertions, 4 deletions

diff --git a/scripts/kconfig/confdata.c b/scripts/kconfig/confdata.c
index a86e71bab5fa..bcce87658998 100644
--- a/scripts/kconfig/confdata.c
+++ b/scripts/kconfig/confdata.c
@@ -810,9 +810,6 @@ int conf_write_defconfig(const char *filename)
 			/*
 			 * If symbol is a choice value and equals to the
 			 * default for a choice - skip.
-			 * But only if value is bool and equal to "y" and
-			 * choice is not "optional".
-			 * (If choice is "optional" then all values can be "n")
 			 */
 			if (sym_is_choice_value(sym)) {
 				struct symbol *cs;
@@ -820,7 +817,7 @@ int conf_write_defconfig(const char *filename)
 
 				cs = prop_get_symbol(sym_get_choice_prop(sym));
 				ds = sym_choice_default(cs);
-				if (!sym_is_optional(cs) && sym == ds) {
+				if (sym == ds) {
 					if ((sym->type == S_BOOLEAN) &&
 					    sym_get_tristate_value(sym) == yes)
 						continue;