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>

Documentation/kbuild/kconfig-language.rst

@@ -410,9 +410,6 @@ to be set to 'm'. This can be used if multiple drivers for a single
 hardware exists and only a single driver can be compiled/loaded into
 the kernel, but all drivers can be compiled as modules.
 
-A choice accepts another option "optional", which allows to set the
-choice to 'n' and no entry needs to be selected.
-
 comment::
 
 	"comment" <prompt>

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;

scripts/kconfig/expr.h

@@ -132,7 +132,6 @@ struct symbol {
 #define SYMBOL_CHECK      0x0008  /* used during dependency checking */
 #define SYMBOL_CHOICEVAL  0x0020  /* used as a value in a choice block */
 #define SYMBOL_VALID      0x0080  /* set when symbol.curr is calculated */
-#define SYMBOL_OPTIONAL   0x0100  /* choice is optional - values can be 'n' */
 #define SYMBOL_WRITE      0x0200  /* write symbol to file (KCONFIG_CONFIG) */
 #define SYMBOL_CHANGED    0x0400  /* ? */
 #define SYMBOL_WRITTEN    0x0800  /* track info to avoid double-write to .config */

scripts/kconfig/gconf.c

@@ -87,8 +87,6 @@ static const char *dbg_sym_flags(int val)
 		strcat(buf, "choiceval/");
 	if (val & SYMBOL_VALID)
 		strcat(buf, "valid/");
-	if (val & SYMBOL_OPTIONAL)
-		strcat(buf, "optional/");
 	if (val & SYMBOL_WRITE)
 		strcat(buf, "write/");
 	if (val & SYMBOL_CHANGED)

scripts/kconfig/lexer.l

@@ -120,7 +120,6 @@ n	[A-Za-z0-9_-]
 "menuconfig"		return T_MENUCONFIG;
 "modules"		return T_MODULES;
 "on"			return T_ON;
-"optional"		return T_OPTIONAL;
 "prompt"		return T_PROMPT;
 "range"			return T_RANGE;
 "select"		return T_SELECT;

scripts/kconfig/lkc.h

@@ -138,11 +138,6 @@ static inline bool sym_is_choice_value(struct symbol *sym)
 	return sym->flags & SYMBOL_CHOICEVAL ? true : false;
 }
 
-static inline bool sym_is_optional(struct symbol *sym)
-{
-	return sym->flags & SYMBOL_OPTIONAL ? true : false;
-}
-
 static inline bool sym_has_value(struct symbol *sym)
 {
 	return sym->flags & SYMBOL_DEF_USER ? true : false;

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
+	 * For choices, add a reverse dependency (corresponding to a select) of
-	 * a select) of '<visibility> && m'. This prevents the user from
+	 * '<visibility> && m'. This prevents the user from setting the choice
-	 * setting the choice mode to 'n' when the choice is visible.
+	 * 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) {
+	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)));

scripts/kconfig/parser.y

@@ -69,7 +69,6 @@ struct menu *current_menu, *current_entry;
 %token T_MODULES
 %token T_ON
 %token T_OPEN_PAREN
-%token T_OPTIONAL
 %token T_PLUS_EQUAL
 %token T_PROMPT
 %token T_RANGE
@@ -140,7 +139,6 @@ stmt_list_in_choice:
 
 config_entry_start: T_CONFIG nonconst_symbol T_EOL
 {
-	$2->flags |= SYMBOL_OPTIONAL;
 	menu_add_entry($2);
 	printd(DEBUG_PARSE, "%s:%d:config %s\n", cur_filename, cur_lineno, $2->name);
 };
@@ -152,7 +150,6 @@ config_stmt: config_entry_start config_option_list
 
 menuconfig_entry_start: T_MENUCONFIG nonconst_symbol T_EOL
 {
-	$2->flags |= SYMBOL_OPTIONAL;
 	menu_add_entry($2);
 	printd(DEBUG_PARSE, "%s:%d:menuconfig %s\n", cur_filename, cur_lineno, $2->name);
 };
@@ -272,12 +269,6 @@ choice_option: logic_type prompt_stmt_opt T_EOL
 	printd(DEBUG_PARSE, "%s:%d:type(%u)\n", cur_filename, cur_lineno, $1);
 };
 
-choice_option: T_OPTIONAL T_EOL
-{
-	current_entry->sym->flags |= SYMBOL_OPTIONAL;
-	printd(DEBUG_PARSE, "%s:%d:optional\n", cur_filename, cur_lineno);
-};
-
 choice_option: T_DEFAULT nonconst_symbol if_expr T_EOL
 {
 	menu_add_symbol(P_DEFAULT, $2, $3);

scripts/kconfig/tests/choice/Kconfig

@@ -17,19 +17,6 @@ config BOOL_CHOICE1
 
 endchoice
 
-choice
-	prompt "optional boolean choice"
-	optional
-	default OPT_BOOL_CHOICE1
-
-config OPT_BOOL_CHOICE0
-	bool "choice 0"
-
-config OPT_BOOL_CHOICE1
-	bool "choice 1"
-
-endchoice
-
 choice
 	prompt "tristate choice"
 	default TRI_CHOICE1
@@ -41,16 +28,3 @@ config TRI_CHOICE1
 	tristate "choice 1"
 
 endchoice
-
-choice
-	prompt "optional tristate choice"
-	optional
-	default OPT_TRI_CHOICE1
-
-config OPT_TRI_CHOICE0
-	tristate "choice 0"
-
-config OPT_TRI_CHOICE1
-	tristate "choice 1"
-
-endchoice

scripts/kconfig/tests/choice/__init__.py

@@ -6,8 +6,6 @@ The handling of 'choice' is a bit complicated part in Kconfig.
 
 The behavior of 'y' choice is intuitive.  If choice values are tristate,
 the choice can be 'm' where each value can be enabled independently.
-Also, if a choice is marked as 'optional', the whole choice can be
-invisible.
 """
 
 

scripts/kconfig/tests/choice/allmod_expected_config

@@ -1,9 +1,5 @@
 CONFIG_MODULES=y
 # CONFIG_BOOL_CHOICE0 is not set
 CONFIG_BOOL_CHOICE1=y
-# CONFIG_OPT_BOOL_CHOICE0 is not set
-CONFIG_OPT_BOOL_CHOICE1=y
 CONFIG_TRI_CHOICE0=m
 CONFIG_TRI_CHOICE1=m
-CONFIG_OPT_TRI_CHOICE0=m
-CONFIG_OPT_TRI_CHOICE1=m

scripts/kconfig/tests/choice/allyes_expected_config

@@ -1,9 +1,5 @@
 CONFIG_MODULES=y
 # CONFIG_BOOL_CHOICE0 is not set
 CONFIG_BOOL_CHOICE1=y
-# CONFIG_OPT_BOOL_CHOICE0 is not set
-CONFIG_OPT_BOOL_CHOICE1=y
 # CONFIG_TRI_CHOICE0 is not set
 CONFIG_TRI_CHOICE1=y
-# CONFIG_OPT_TRI_CHOICE0 is not set
-CONFIG_OPT_TRI_CHOICE1=y

scripts/kconfig/tests/choice/oldask0_expected_stdout

@@ -3,8 +3,6 @@ boolean choice
   1. choice 0 (BOOL_CHOICE0) (NEW)
 > 2. choice 1 (BOOL_CHOICE1) (NEW)
 choice[1-2?]: 
-optional boolean choice [N/y/?] (NEW) 
 tristate choice [M/y/?] (NEW) 
   choice 0 (TRI_CHOICE0) [N/m/?] (NEW) 
   choice 1 (TRI_CHOICE1) [N/m/?] (NEW) 
-optional tristate choice [N/m/y/?] (NEW) 

scripts/kconfig/tests/choice/oldask1_config

@@ -1,2 +1 @@
 # CONFIG_MODULES is not set
-CONFIG_OPT_BOOL_CHOICE0=y

scripts/kconfig/tests/choice/oldask1_expected_stdout

@@ -3,13 +3,7 @@ boolean choice
   1. choice 0 (BOOL_CHOICE0) (NEW)
 > 2. choice 1 (BOOL_CHOICE1) (NEW)
 choice[1-2?]: 
-optional boolean choice [Y/n/?] (NEW) 
-optional boolean choice
-> 1. choice 0 (OPT_BOOL_CHOICE0)
-  2. choice 1 (OPT_BOOL_CHOICE1) (NEW)
-choice[1-2?]: 
 tristate choice
   1. choice 0 (TRI_CHOICE0) (NEW)
 > 2. choice 1 (TRI_CHOICE1) (NEW)
 choice[1-2?]: 
-optional tristate choice [N/y/?]