kconfig: remove tristate choice support

I previously submitted a fix for a bug in the choice feature [1], where
I mentioned, "Another (much cleaner) approach would be to remove the
tristate choice support entirely".

There are more issues in the tristate choice feature. For example, you
can observe a couple of bugs in the following test code.

[Test Code]

config MODULES
def_bool y
modules

choice
prompt "tristate choice"
default A

config A
tristate "A"

config B
tristate "B"

endchoice

Bug 1: the 'default' property is not correctly processed

'make alldefconfig' produces:

CONFIG_MODULES=y
# CONFIG_A is not set
# CONFIG_B is not set

However, the correct output should be:

CONFIG_MODULES=y
CONFIG_A=y
# CONFIG_B is not set

The unit test file, scripts/kconfig/tests/choice/alldef_expected_config,
is wrong as well.

Bug 2: choice members never get 'y' with randconfig

For the test code above, the following combinations are possible:

A B
(1) y n
(2) n y
(3) m m
(4) m n
(5) n m
(6) n n

'make randconfig' never produces (1) or (2).

These bugs are fixable, but a more critical problem is the lack of a
sensible syntax to specify the default for the tristate choice.
The default for the choice must be one of the choice members, which
cannot specify any of the patterns (3) through (6) above.

In addition, I have never seen it being used in a useful way.

The following commits removed unnecessary use of tristate choices:

- df8df5e4bc37 ("usb: get rid of 'choice' for legacy gadget drivers")
- bfb57ef0544a ("rapidio: remove choice for enumeration")

This commit removes the tristate choice support entirely, which allows
me to delete a lot of code, making further refactoring easier.

Note:
This includes the revert of commit fa64e5f6a35e ("kconfig/symbol.c:
handle choice_values that depend on 'm' symbols"). It was suspicious
because it did not address the root cause but introduced inconsistency
in visibility between choice members and other symbols.

[1]: https://lore.kernel.org/linux-kbuild/[e-mail]/T/#m0a1bb6992581462ceca861b409bb33cb8fd7dbae

Signed-off-by: Masahiro Yamada <[e-mail]>
Reviewed-by: Nicolas Schier <[e-mail]>

Documentation/kbuild/kconfig-language.rst

···
 	"endchoice"
 
 This defines a choice group and accepts any of the above attributes as
-options. A choice can only be of type bool or tristate.  If no type is
-specified for a choice, its type will be determined by the type of
-the first choice element in the group or remain unknown if none of the
-choice elements have a type specified, as well.
+options.
 
-While a boolean choice only allows a single config entry to be
-selected, a tristate choice also allows any number of config entries
-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 only allows a single config entry to be selected.
 
 comment::
 

scripts/kconfig/conf.c

···
 	srand(seed);
 }
 
-static bool randomize_choice_values(struct symbol *csym)
+static void randomize_choice_values(struct symbol *csym)
 {
 	struct property *prop;
 	struct symbol *sym;
 	struct expr *e;
 	int cnt, def;
-
-	/*
-	 * If choice is mod then we may have more items selected
-	 * and if no then no-one.
-	 * In both cases stop.
-	 */
-	if (csym->curr.tri != yes)
-		return false;
 
 	prop = sym_get_choice_prop(csym);
 
···
 	csym->flags |= SYMBOL_DEF_USER;
 	/* clear VALID to get value calculated */
 	csym->flags &= ~SYMBOL_VALID;
-
-	return true;
 }
 
 enum conf_def_mode {
···
 
 	sym_clear_all_valid();
 
-	/*
-	 * We have different type of choice blocks.
-	 * If curr.tri equals to mod then we can select several
-	 * choice symbols in one block.
-	 * In this case we do nothing.
-	 * If curr.tri equals yes then only one symbol can be
-	 * selected in a choice block and we set it to yes,
-	 * and the rest to no.
-	 */
 	if (mode != def_random) {
 		for_all_symbols(csym) {
 			if ((sym_is_choice(csym) && !sym_has_value(csym)) ||
···
 
 		sym_calc_value(csym);
 		if (mode == def_random)
-			has_changed |= randomize_choice_values(csym);
-		else {
+			randomize_choice_values(csym);
+		else
 			set_all_choice_values(csym);
-			has_changed = true;
-		}
+		has_changed = true;
 	}
 
 	return has_changed;
···
 
 	sym = menu->sym;
 	is_new = !sym_has_value(sym);
-	if (sym_is_changeable(sym)) {
-		conf_sym(menu);
-		sym_calc_value(sym);
-		switch (sym_get_tristate_value(sym)) {
-		case no:
-		case mod:
-			return;
-		case yes:
-			break;
-		}
-	} else {
-		switch (sym_get_tristate_value(sym)) {
-		case no:
-			return;
-		case mod:
-			printf("%*s%s\n", indent - 1, "", menu_get_prompt(menu));
-			return;
-		case yes:
-			break;
-		}
-	}
 
 	while (1) {
 		int cnt, def;
···
 
 	if (sym_is_choice(sym)) {
 		conf_choice(menu);
-		if (sym->curr.tri != mod)
-			return;
-		goto conf_childs;
+		return;
 	}
 
 	switch (sym->type) {
···
 
 	sym = menu->sym;
 	if (sym && !sym_has_value(sym) &&
-	    (sym_is_changeable(sym) ||
-	     (sym_is_choice(sym) && sym_get_tristate_value(sym) == yes))) {
+	    (sym_is_changeable(sym) || sym_is_choice(sym))) {
 
 		switch (input_mode) {
 		case listnewconfig:

scripts/kconfig/confdata.c

···
 
 		if (sym && sym_is_choice_value(sym)) {
 			struct symbol *cs = prop_get_symbol(sym_get_choice_prop(sym));
-			switch (sym->def[def].tri) {
-			case no:
-				break;
-			case mod:
-				if (cs->def[def].tri == yes) {
-					conf_warning("%s creates inconsistent choice state", sym->name);
-					cs->flags &= ~def_flags;
-				}
-				break;
-			case yes:
+			if (sym->def[def].tri == yes) {
 				if (cs->def[def].tri != no)
 					conf_warning("override: %s changes choice state", sym->name);
 				cs->def[def].val = sym;
-				break;
+				cs->def[def].tri = yes;
 			}
-			cs->def[def].tri = EXPR_OR(cs->def[def].tri, sym->def[def].tri);
 		}
 	}
 	free(line);
···
 
 				ds = sym_choice_default(choice->sym);
 				if (sym == ds) {
-					if ((sym->type == S_BOOLEAN) &&
-					    sym_get_tristate_value(sym) == yes)
+					if (sym_get_tristate_value(sym) == yes)
 						continue;
 				}
 			}

scripts/kconfig/gconf.c

···
 			row[COL_VALUE] =
 			    g_strdup(menu_get_prompt(def_menu));
 
-		if (sym_get_type(sym) == S_BOOLEAN) {
-			row[COL_BTNVIS] = GINT_TO_POINTER(FALSE);
-			return row;
-		}
+		row[COL_BTNVIS] = GINT_TO_POINTER(FALSE);
+		return row;
 	}
 	if (sym->flags & SYMBOL_CHOICEVAL)
 		row[COL_BTNRAD] = GINT_TO_POINTER(TRUE);

scripts/kconfig/mconf.c

···
 				def_menu = child;
 		}
 
-		val = sym_get_tristate_value(sym);
-		if (sym_is_changeable(sym)) {
-			switch (val) {
-			case yes: ch = '*'; break;
-			case mod: ch = 'M'; break;
-			default:  ch = ' '; break;
-			}
-			item_make("<%c>", ch);
-			item_set_tag('t');
-			item_set_data(menu);
-		} else {
-			item_make("   ");
-			item_set_tag(def_menu ? 't' : ':');
-			item_set_data(menu);
-		}
+		item_make("   ");
+		item_set_tag(def_menu ? 't' : ':');
+		item_set_data(menu);
 
 		item_add_str("%*c%s", indent + 1, ' ', menu_get_prompt(menu));
-		if (val == yes) {
-			if (def_menu)
-				item_add_str(" (%s)  --->", menu_get_prompt(def_menu));
-			return;
-		}
+		if (def_menu)
+			item_add_str(" (%s)  --->", menu_get_prompt(def_menu));
+		return;
 	} else {
 		if (menu == current_menu) {
 			item_make("---%*c%s", indent + 1, ' ', menu_get_prompt(menu));
···
 					conf(submenu, NULL);
 				break;
 			case 't':
-				if (sym_is_choice(sym) && sym_get_tristate_value(sym) == yes)
+				if (sym_is_choice(sym))
 					conf_choice(submenu);
 				else if (submenu->prompt->type == P_MENU)
 					conf(submenu, NULL);

scripts/kconfig/menu.c

···
 			is_choice = true;
 
 		if (is_choice) {
-			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;
-					}
-				}
-			}
-
 			/*
 			 * Use the choice itself as the parent dependency of
 			 * the contained items. This turns the mode of the
···
 		    menu->sym && !sym_is_choice_value(menu->sym)) {
 			current_entry = menu;
 			menu->sym->flags |= SYMBOL_CHOICEVAL;
-			/* 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)
···
 
 	/*
 	 * For choices, add a reverse dependency (corresponding to a select) of
-	 * '<visibility> && m'. This prevents the user from setting the choice
+	 * '<visibility> && y'. This prevents the user from setting the choice
 	 * mode to 'n' when the choice is visible.
 	 */
 	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)));
+					expr_alloc_symbol(&symbol_yes)));
 	}
 }
 

scripts/kconfig/nconf.c

···
 		}
 
 		val = sym_get_tristate_value(sym);
-		if (sym_is_changeable(sym)) {
-			switch (val) {
-			case yes:
-				ch = '*';
-				break;
-			case mod:
-				ch = 'M';
-				break;
-			default:
-				ch = ' ';
-				break;
-			}
-			item_make(menu, 't', "<%c>", ch);
-		} else {
-			item_make(menu, def_menu ? 't' : ':', "   ");
-		}
+		item_make(menu, def_menu ? 't' : ':', "   ");
 
 		item_add_str("%*c%s", indent + 1,
 				' ', menu_get_prompt(menu));
-		if (val == yes) {
-			if (def_menu)
-				item_add_str(" (%s)  --->", menu_get_prompt(def_menu));
-			return;
-		}
+		if (def_menu)
+			item_add_str(" (%s)  --->", menu_get_prompt(def_menu));
+		return;
 	} else {
 		if (menu == current_menu) {
 			item_make(menu, ':',
···
 					conf(submenu);
 				break;
 			case 't':
-				if (sym_is_choice(sym) &&
-				    sym_get_tristate_value(sym) == yes)
+				if (sym_is_choice(sym))
 					conf_choice(submenu);
 				else if (submenu->prompt &&
 					 submenu->prompt->type == P_MENU)

scripts/kconfig/parser.y

···
 
 %type <symbol> nonconst_symbol
 %type <symbol> symbol
-%type <type> type logic_type default
+%type <type> type default
 %type <expr> expr
 %type <expr> if_expr
 %type <string> end
···
 	if (inside_choice) {
 		if (!current_entry->prompt) {
 			fprintf(stderr, "%s:%d: error: choice member must have a prompt\n",
+				current_entry->filename, current_entry->lineno);
+			yynerrs++;
+		}
+
+		if (current_entry->sym->type != S_BOOLEAN) {
+			fprintf(stderr, "%s:%d: error: choice member must be bool\n",
 				current_entry->filename, current_entry->lineno);
 			yynerrs++;
 		}
···
 
 	menu_add_entry(sym);
 	menu_add_expr(P_CHOICE, NULL, NULL);
+	menu_set_type(S_BOOLEAN);
+
 	printd(DEBUG_PARSE, "%s:%d:choice\n", cur_filename, cur_lineno);
 };
 
···
 	printd(DEBUG_PARSE, "%s:%d:prompt\n", cur_filename, cur_lineno);
 };
 
-choice_option: logic_type prompt_stmt_opt T_EOL
+choice_option: T_BOOL T_WORD_QUOTE if_expr T_EOL
 {
-	menu_set_type($1);
-	printd(DEBUG_PARSE, "%s:%d:type(%u)\n", cur_filename, cur_lineno, $1);
+	menu_add_prompt(P_PROMPT, $2, $3);
+	printd(DEBUG_PARSE, "%s:%d:bool\n", cur_filename, cur_lineno);
 };
 
 choice_option: T_DEFAULT nonconst_symbol if_expr T_EOL
···
 };
 
 type:
-	  logic_type
+	  T_BOOL		{ $$ = S_BOOLEAN; }
+	| T_TRISTATE		{ $$ = S_TRISTATE; }
 	| T_INT			{ $$ = S_INT; }
 	| T_HEX			{ $$ = S_HEX; }
 	| T_STRING		{ $$ = S_STRING; }
-
-logic_type:
-	  T_BOOL		{ $$ = S_BOOLEAN; }
-	| T_TRISTATE		{ $$ = S_TRISTATE; }
 
 default:
 	  T_DEFAULT		{ $$ = S_UNKNOWN; }

scripts/kconfig/qconf.cc

···
 		expr = sym_get_tristate_value(sym);
 		switch (expr) {
 		case yes:
-			if (sym_is_choice_value(sym) && type == S_BOOLEAN)
+			if (sym_is_choice_value(sym))
 				setIcon(promptColIdx, choiceYesIcon);
 			else
 				setIcon(promptColIdx, symbolYesIcon);

scripts/kconfig/symbol.c

···
 {
 	enum symbol_type type = sym->type;
 
-	if (type == S_TRISTATE) {
-		if (sym_is_choice_value(sym) && sym->visible == yes)
-			type = S_BOOLEAN;
-		else if (modules_val == no)
-			type = S_BOOLEAN;
-	}
+	if (type == S_TRISTATE && modules_val == no)
+		type = S_BOOLEAN;
 	return type;
 }
 
···
 static void sym_calc_visibility(struct symbol *sym)
 {
 	struct property *prop;
-	struct symbol *choice_sym = NULL;
 	tristate tri;
 
 	/* any prompt visible? */
 	tri = no;
-
-	if (sym_is_choice_value(sym))
-		choice_sym = prop_get_symbol(sym_get_choice_prop(sym));
-
 	for_all_prompts(sym, prop) {
 		prop->visible.tri = expr_calc_value(prop->visible.expr);
-		/*
-		 * Tristate choice_values with visibility 'mod' are
-		 * not visible if the corresponding choice's value is
-		 * 'yes'.
-		 */
-		if (choice_sym && sym->type == S_TRISTATE &&
-		    prop->visible.tri == mod && choice_sym->curr.tri == yes)
-			prop->visible.tri = no;
-
 		tri = EXPR_OR(tri, prop->visible.tri);
 	}
 	if (tri == mod && (sym->type != S_TRISTATE || modules_val == no))

scripts/kconfig/tests/choice/Kconfig

···
 # SPDX-License-Identifier: GPL-2.0
 
-config MODULES
-	bool "Enable loadable module support"
-	modules
-	default y
-
 choice
 	prompt "boolean choice"
 	default BOOL_CHOICE1
···
 
 config BOOL_CHOICE1
 	bool "choice 1"
-
-endchoice
-
-choice
-	prompt "tristate choice"
-	default TRI_CHOICE1
-
-config TRI_CHOICE0
-	tristate "choice 0"
-
-config TRI_CHOICE1
-	tristate "choice 1"
 
 endchoice

scripts/kconfig/tests/choice/__init__.py

···
 # SPDX-License-Identifier: GPL-2.0
 """
 Basic choice tests.
-
-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.
 """
 
 
 def test_oldask0(conf):
     assert conf.oldaskconfig() == 0
     assert conf.stdout_contains('oldask0_expected_stdout')
-
-
-def test_oldask1(conf):
-    assert conf.oldaskconfig('oldask1_config') == 0
-    assert conf.stdout_contains('oldask1_expected_stdout')
 
 
 def test_allyes(conf):

scripts/kconfig/tests/choice/alldef_expected_config

···
-CONFIG_MODULES=y
 # CONFIG_BOOL_CHOICE0 is not set
 CONFIG_BOOL_CHOICE1=y
-# CONFIG_TRI_CHOICE0 is not set
-# CONFIG_TRI_CHOICE1 is not set

scripts/kconfig/tests/choice/allmod_expected_config

···
-CONFIG_MODULES=y
 # CONFIG_BOOL_CHOICE0 is not set
 CONFIG_BOOL_CHOICE1=y
-CONFIG_TRI_CHOICE0=m
-CONFIG_TRI_CHOICE1=m

scripts/kconfig/tests/choice/allno_expected_config

···
-# CONFIG_MODULES is not set
 # CONFIG_BOOL_CHOICE0 is not set
 CONFIG_BOOL_CHOICE1=y
-# CONFIG_TRI_CHOICE0 is not set
-CONFIG_TRI_CHOICE1=y

scripts/kconfig/tests/choice/allyes_expected_config

···
-CONFIG_MODULES=y
 # CONFIG_BOOL_CHOICE0 is not set
 CONFIG_BOOL_CHOICE1=y
-# CONFIG_TRI_CHOICE0 is not set
-CONFIG_TRI_CHOICE1=y

scripts/kconfig/tests/choice/oldask0_expected_stdout

···
-Enable loadable module support (MODULES) [Y/n/?] (NEW) 
 boolean choice
   1. choice 0 (BOOL_CHOICE0) (NEW)
 > 2. choice 1 (BOOL_CHOICE1) (NEW)
 choice[1-2?]: 
-tristate choice [M/y/?] (NEW) 
-  choice 0 (TRI_CHOICE0) [N/m/?] (NEW) 
-  choice 1 (TRI_CHOICE1) [N/m/?] (NEW) 

scripts/kconfig/tests/choice/oldask1_config

···
-# CONFIG_MODULES is not set

scripts/kconfig/tests/choice/oldask1_expected_stdout

···
-Enable loadable module support (MODULES) [N/y/?] 
-boolean choice
-  1. choice 0 (BOOL_CHOICE0) (NEW)
-> 2. choice 1 (BOOL_CHOICE1) (NEW)
-choice[1-2?]: 
-tristate choice
-  1. choice 0 (TRI_CHOICE0) (NEW)
-> 2. choice 1 (TRI_CHOICE1) (NEW)
-choice[1-2?]: 

scripts/kconfig/tests/choice_value_with_m_dep/Kconfig

···
-# SPDX-License-Identifier: GPL-2.0
-
-config MODULES
-	def_bool y
-	modules
-
-config DEP
-	tristate
-	default m
-
-choice
-	prompt "Tristate Choice"
-
-config CHOICE0
-	tristate "Choice 0"
-
-config CHOICE1
-	tristate "Choice 1"
-	depends on DEP
-
-endchoice

scripts/kconfig/tests/choice_value_with_m_dep/__init__.py

···
-# SPDX-License-Identifier: GPL-2.0
-"""
-Hide tristate choice values with mod dependency in y choice.
-
-If tristate choice values depend on symbols set to 'm', they should be
-hidden when the choice containing them is changed from 'm' to 'y'
-(i.e. exclusive choice).
-
-Related Linux commit: fa64e5f6a35efd5e77d639125d973077ca506074
-"""
-
-
-def test(conf):
-    assert conf.oldaskconfig('config', 'y') == 0
-    assert conf.config_contains('expected_config')
-    assert conf.stdout_contains('expected_stdout')

scripts/kconfig/tests/choice_value_with_m_dep/config

···
-CONFIG_CHOICE0=m
-CONFIG_CHOICE1=m

scripts/kconfig/tests/choice_value_with_m_dep/expected_config

···
-CONFIG_MODULES=y
-CONFIG_DEP=m
-CONFIG_CHOICE0=y

scripts/kconfig/tests/choice_value_with_m_dep/expected_stdout

···
-Tristate Choice [M/y/?] y
-Tristate Choice
-> 1. Choice 0 (CHOICE0)
-choice[1]: 1

scripts/kconfig/tests/inter_choice/Kconfig

···
-# SPDX-License-Identifier: GPL-2.0
-
-config MODULES
-	def_bool y
-	modules
-
-choice
-	prompt "Choice"
-
-config CHOICE_VAL0
-	tristate "Choice 0"
-
-config CHOIVE_VAL1
-	tristate "Choice 1"
-
-endchoice
-
-choice
-	prompt "Another choice"
-	depends on CHOICE_VAL0
-
-config DUMMY
-	bool "dummy"
-
-endchoice

scripts/kconfig/tests/inter_choice/__init__.py

···
-# SPDX-License-Identifier: GPL-2.0
-"""
-Do not affect user-assigned choice value by another choice.
-
-Handling of state flags for choices is complecated.  In old days,
-the defconfig result of a choice could be affected by another choice
-if those choices interact by 'depends on', 'select', etc.
-
-Related Linux commit: fbe98bb9ed3dae23e320c6b113e35f129538d14a
-"""
-
-
-def test(conf):
-    assert conf.defconfig('defconfig') == 0
-    assert conf.config_contains('expected_config')

scripts/kconfig/tests/inter_choice/defconfig

···
-CONFIG_CHOICE_VAL0=y

scripts/kconfig/tests/inter_choice/expected_config

···
-CONFIG_MODULES=y
-CONFIG_CHOICE_VAL0=y
-# CONFIG_CHOIVE_VAL1 is not set
-CONFIG_DUMMY=y