kconfig: Add "def_string", "def_int" and "def_hex"

Kconfig has offered "def_bool" and "def_tristate" as a shorthand for a
type definition plus a default since before the git era, but has never
offered the equivalent for the other three types. Conor Dooley ran into
this gap[1] when fixing a symbol that had been given the wrong type:

  Unfortunately, there is no such thing as "def_string", but in this
  case we can use "default" to propagate the value of ...

Nothing in the grammar requires the restriction. The rule that consumes
a default is already type agnostic. Add the three missing types. No
changes are needed to existing diagnostics. E.g. declaring a symbol
"bool" and then assigning it with "def_string" still reports

  warning: ignoring type redefinition of 'CONFLICT' from 'bool' to 'string'

Added tests for the types.

Build tested ARCH=x86_64 with GCC 16.2.0. Tests pass with "make testconfig".

Link: https://lore.kernel.org/all/20230111104848.2088516-1-conor.dooley@microchip.com/ [1]
Assisted-by: LLM
Signed-off-by: Kees Cook <kees@kernel.org>
Tested-by: Julian Braha <julianbraha@gmail.com>
Reviewed-by: Julian Braha <julianbraha@gmail.com>
Link: https://patch.msgid.link/20260919005929.4077729-1-kees@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Documentation/kbuild/kconfig-language.rst

@@ -113,11 +113,22 @@ applicable everywhere (see syntax).
 
 - type definition + default value::
 
-	"def_bool"/"def_tristate" <expr> ["if" <expr>]
+	"def_bool" <expr> ["if" <expr>]
+	"def_tristate" <expr> ["if" <expr>]
+	"def_string" <expr> ["if" <expr>]
+	"def_int" <expr> ["if" <expr>]
+	"def_hex" <expr> ["if" <expr>]
 
   This is a shorthand notation for a type definition plus a value.
   Optionally dependencies for this default value can be added with "if".
 
+  The shorthand supplies the type once, and is otherwise an ordinary
+  default: it is the first entry of the list described above, so any
+  further "default" entries still apply when its "if" is not met. Since
+  that leaves the type definition inside one arm of a list, spelling the
+  type out on its own line reads better for a symbol with several
+  defaults.
+
 - dependencies: "depends on" <expr> ["if" <expr>]
 
   This defines a dependency for this menu entry. If multiple

scripts/kconfig/kconfig-sym-check.pl

@@ -90,7 +90,7 @@ foreach my $file (@files) {
 			next;
 		}
 
-		if (/^\s*(default|def_bool|def_tristate|select|depends\s+on|imply|visible\s+if|range|if|bool|tristate|int|hex|string|prompt)\s+(.+)\s*$/) {
+		if (/^\s*(default|def_bool|def_tristate|def_string|def_int|def_hex|select|depends\s+on|imply|visible\s+if|range|if|bool|tristate|int|hex|string|prompt)\s+(.+)\s*$/) {
 			my $s = $2;
 			$s =~ s/"(?:[^"\\]|\\.)*"|'(?:[^'\\]|\\.)*'//g;
 			$s =~ s/#.*//;

scripts/kconfig/lexer.l

@@ -105,6 +105,9 @@ n	[A-Za-z0-9_-]
 "comment"		return T_COMMENT;
 "config"		return T_CONFIG;
 "def_bool"		return T_DEF_BOOL;
+"def_hex"		return T_DEF_HEX;
+"def_int"		return T_DEF_INT;
+"def_string"		return T_DEF_STRING;
 "def_tristate"		return T_DEF_TRISTATE;
 "default"		return T_DEFAULT;
 "depends"		return T_DEPENDS;

scripts/kconfig/parser.y

@@ -53,6 +53,9 @@ struct menu *current_menu, *current_entry, *current_choice;
 %token T_CONFIG
 %token T_DEFAULT
 %token T_DEF_BOOL
+%token T_DEF_HEX
+%token T_DEF_INT
+%token T_DEF_STRING
 %token T_DEF_TRISTATE
 %token T_DEPENDS
 %token T_ENDCHOICE
@@ -309,6 +312,9 @@ type:
 default:
 	  T_DEFAULT		{ $$ = S_UNKNOWN; }
 	| T_DEF_BOOL		{ $$ = S_BOOLEAN; }
+	| T_DEF_HEX		{ $$ = S_HEX; }
+	| T_DEF_INT		{ $$ = S_INT; }
+	| T_DEF_STRING		{ $$ = S_STRING; }
 	| T_DEF_TRISTATE	{ $$ = S_TRISTATE; }
 
 /* if entry */

scripts/kconfig/tests/def_type/Kconfig

@@ -0,0 +1,28 @@
+# SPDX-License-Identifier: GPL-2.0
+# The def_<type> shorthands: a type definition plus a default value.
+
+config MODULES
+	bool "Enable loadable module support"
+	modules
+	default y
+
+config GUARD
+	bool "Guard symbol"
+
+config DEF_BOOL
+	def_bool GUARD
+
+config DEF_TRISTATE
+	def_tristate m if GUARD
+
+config DEF_STRING
+	def_string "guarded" if GUARD
+	default "fallback"
+
+config DEF_INT
+	def_int 64 if GUARD
+	default 32
+
+config DEF_HEX
+	def_hex 0xdead if GUARD
+	default 0x0

scripts/kconfig/tests/def_type/__init__.py

@@ -0,0 +1,18 @@
+# SPDX-License-Identifier: GPL-2.0
+"""
+Set a symbol's type and its default value in one line.
+
+"def_bool", "def_tristate", "def_string", "def_int" and "def_hex" are
+shorthand for a type definition plus a "default" property.  Check that
+each one sets the type, and that an "if" on the shorthand does not
+disturb the usual default cascade: the shorthand is only the first arm
+of the list, so a later "default" still applies when its condition is
+not met.
+"""
+
+def test(conf):
+    assert conf.olddefconfig(dot_config='guard_y.config') == 0
+    assert conf.config_matches('expected_guard_y')
+
+    assert conf.olddefconfig(dot_config='guard_n.config') == 0
+    assert conf.config_matches('expected_guard_n')

scripts/kconfig/tests/def_type/expected_guard_n

@@ -0,0 +1,9 @@
+#
+# Automatically generated file; DO NOT EDIT.
+# Main menu
+#
+CONFIG_MODULES=y
+# CONFIG_GUARD is not set
+CONFIG_DEF_STRING="fallback"
+CONFIG_DEF_INT=32
+CONFIG_DEF_HEX=0x0

scripts/kconfig/tests/def_type/expected_guard_y

@@ -0,0 +1,11 @@
+#
+# Automatically generated file; DO NOT EDIT.
+# Main menu
+#
+CONFIG_MODULES=y
+CONFIG_GUARD=y
+CONFIG_DEF_BOOL=y
+CONFIG_DEF_TRISTATE=m
+CONFIG_DEF_STRING="guarded"
+CONFIG_DEF_INT=64
+CONFIG_DEF_HEX=0xdead

scripts/kconfig/tests/def_type/guard_n.config

@@ -0,0 +1 @@
+# CONFIG_GUARD is not set

scripts/kconfig/tests/def_type/guard_y.config

@@ -0,0 +1 @@
+CONFIG_GUARD=y