kconfig: Support conditional deps using "depends on X if Y"

Extend the "depends on" syntax to support conditional dependencies
using "depends on X if Y". While functionally equivalent to "depends
on X || (Y == n)", "depends on X if Y" is much more readable and
makes the kconfig language uniform in supporting the "if <expr>"
suffix.
This also improves readability for "optional" dependencies, which
are the subset of conditional dependencies where X is Y.
Previously such optional dependencies had to be expressed as
the counterintuitive "depends on X || !X", now this can be
represented as "depends on X if X".

The change is implemented by converting the "X if Y" syntax into the
"X || (Y == n)" syntax during "depends on" token processing.

Signed-off-by: Nicolas Pitre <nico@fluxnic.net>
[Graham Roff: Rewrote commit message, updated patch, added tests]
Signed-off-by: Graham Roff <grahamr@qti.qualcomm.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://patch.msgid.link/20251215-kconfig_conditional_deps-v3-1-59519af0a5df@qti.qualcomm.com
[nathan: Minor adjustments to spacing]
Signed-off-by: Nathan Chancellor <nathan@kernel.org>

11 files changed, 111 insertions, 5 deletions

diff --git a/scripts/kconfig/lkc.h b/scripts/kconfig/lkc.h
index 56548efc14d7..798985961215 100644
--- a/scripts/kconfig/lkc.h
+++ b/scripts/kconfig/lkc.h
@@ -82,7 +82,7 @@ void menu_warn(const struct menu *menu, const char *fmt, ...);
 struct menu *menu_add_menu(void);
 void menu_end_menu(void);
 void menu_add_entry(struct symbol *sym, enum menu_type type);
-void menu_add_dep(struct expr *dep);
+void menu_add_dep(struct expr *dep, struct expr *cond);
 void menu_add_visibility(struct expr *dep);
 struct property *menu_add_prompt(enum prop_type type, const char *prompt,
 				 struct expr *dep);
diff --git a/scripts/kconfig/menu.c b/scripts/kconfig/menu.c
index 0f1a6513987c..b2d8d4e11e07 100644
--- a/scripts/kconfig/menu.c
+++ b/scripts/kconfig/menu.c
@@ -127,8 +127,18 @@ static struct expr *rewrite_m(struct expr *e)
 	return e;
 }
 
-void menu_add_dep(struct expr *dep)
+void menu_add_dep(struct expr *dep, struct expr *cond)
 {
+	if (cond) {
+		/*
+		 * We have "depends on X if Y" and we want:
+		 *	Y != n --> X
+		 *	Y == n --> y
+		 * That simplifies to: (X || (Y == n))
+		 */
+		dep = expr_alloc_or(dep,
+				expr_trans_compare(cond, E_EQUAL, &symbol_no));
+	}
 	current_entry->dep = expr_alloc_and(current_entry->dep, dep);
 }
 
diff --git a/scripts/kconfig/parser.y b/scripts/kconfig/parser.y
index 49b79dde1725..6d1bbee38f5d 100644
--- a/scripts/kconfig/parser.y
+++ b/scripts/kconfig/parser.y
@@ -323,7 +323,7 @@ if_entry: T_IF expr T_EOL
 {
 	printd(DEBUG_PARSE, "%s:%d:if\n", cur_filename, cur_lineno);
 	menu_add_entry(NULL, M_IF);
-	menu_add_dep($2);
+	menu_add_dep($2, NULL);
 	$$ = menu_add_menu();
 };
 
@@ -422,9 +422,9 @@ help: help_start T_HELPTEXT
 
 /* depends option */
 
-depends: T_DEPENDS T_ON expr T_EOL
+depends: T_DEPENDS T_ON expr if_expr T_EOL
 {
-	menu_add_dep($3);
+	menu_add_dep($3, $4);
 	printd(DEBUG_PARSE, "%s:%d:depends on\n", cur_filename, cur_lineno);
 };
 
diff --git a/scripts/kconfig/tests/conditional_dep/Kconfig b/scripts/kconfig/tests/conditional_dep/Kconfig
new file mode 100644
index 000000000000..2015dfbce2b1
--- /dev/null
+++ b/scripts/kconfig/tests/conditional_dep/Kconfig
@@ -0,0 +1,32 @@
+# SPDX-License-Identifier: GPL-2.0
+# Test Kconfig file for conditional dependencies.
+
+# Enable module support for tristate testing
+config MODULES
+	bool "Enable loadable module support"
+	modules
+	default y
+
+config FOO
+	bool "FOO symbol"
+
+config BAR
+	bool "BAR symbol"
+
+config TEST_BASIC
+	bool "Test basic conditional dependency"
+	depends on FOO if BAR
+	default y
+
+config TEST_COMPLEX
+	bool "Test complex conditional dependency"
+	depends on (FOO && BAR) if (FOO || BAR)
+	default y
+
+config BAZ
+	tristate "BAZ symbol"
+
+config TEST_OPTIONAL
+	tristate "Test simple optional dependency"
+	depends on BAZ if BAZ
+	default y
diff --git a/scripts/kconfig/tests/conditional_dep/__init__.py b/scripts/kconfig/tests/conditional_dep/__init__.py
new file mode 100644
index 000000000000..ab16df6487ec
--- /dev/null
+++ b/scripts/kconfig/tests/conditional_dep/__init__.py
@@ -0,0 +1,14 @@
+# SPDX-License-Identifier: GPL-2.0
+"""
+Correctly handle conditional dependencies.
+"""
+
+def test(conf):
+    assert conf.oldconfig('test_config1') == 0
+    assert conf.config_matches('expected_config1')
+
+    assert conf.oldconfig('test_config2') == 0
+    assert conf.config_matches('expected_config2')
+
+    assert conf.oldconfig('test_config3') == 0
+    assert conf.config_matches('expected_config3')
diff --git a/scripts/kconfig/tests/conditional_dep/expected_config1 b/scripts/kconfig/tests/conditional_dep/expected_config1
new file mode 100644
index 000000000000..826ed7f541b8
--- /dev/null
+++ b/scripts/kconfig/tests/conditional_dep/expected_config1
@@ -0,0 +1,11 @@
+#
+# Automatically generated file; DO NOT EDIT.
+# Main menu
+#
+CONFIG_MODULES=y
+CONFIG_FOO=y
+CONFIG_BAR=y
+CONFIG_TEST_BASIC=y
+CONFIG_TEST_COMPLEX=y
+CONFIG_BAZ=m
+CONFIG_TEST_OPTIONAL=m
diff --git a/scripts/kconfig/tests/conditional_dep/expected_config2 b/scripts/kconfig/tests/conditional_dep/expected_config2
new file mode 100644
index 000000000000..10d2354f687f
--- /dev/null
+++ b/scripts/kconfig/tests/conditional_dep/expected_config2
@@ -0,0 +1,9 @@
+#
+# Automatically generated file; DO NOT EDIT.
+# Main menu
+#
+CONFIG_MODULES=y
+# CONFIG_FOO is not set
+CONFIG_BAR=y
+CONFIG_BAZ=y
+CONFIG_TEST_OPTIONAL=y
diff --git a/scripts/kconfig/tests/conditional_dep/expected_config3 b/scripts/kconfig/tests/conditional_dep/expected_config3
new file mode 100644
index 000000000000..b04fa6fdfeb4
--- /dev/null
+++ b/scripts/kconfig/tests/conditional_dep/expected_config3
@@ -0,0 +1,11 @@
+#
+# Automatically generated file; DO NOT EDIT.
+# Main menu
+#
+CONFIG_MODULES=y
+# CONFIG_FOO is not set
+# CONFIG_BAR is not set
+CONFIG_TEST_BASIC=y
+CONFIG_TEST_COMPLEX=y
+# CONFIG_BAZ is not set
+CONFIG_TEST_OPTIONAL=y
diff --git a/scripts/kconfig/tests/conditional_dep/test_config1 b/scripts/kconfig/tests/conditional_dep/test_config1
new file mode 100644
index 000000000000..9b05f3ce8a99
--- /dev/null
+++ b/scripts/kconfig/tests/conditional_dep/test_config1
@@ -0,0 +1,6 @@
+# Basic check that everything can be configured if selected.
+CONFIG_FOO=y
+CONFIG_BAR=y
+CONFIG_BAZ=m
+# Ensure that TEST_OPTIONAL=y with BAZ=m is converted to TEST_OPTIONAL=m
+CONFIG_TEST_OPTIONAL=y
diff --git a/scripts/kconfig/tests/conditional_dep/test_config2 b/scripts/kconfig/tests/conditional_dep/test_config2
new file mode 100644
index 000000000000..5e66d230a836
--- /dev/null
+++ b/scripts/kconfig/tests/conditional_dep/test_config2
@@ -0,0 +1,7 @@
+# If FOO is not selected, then TEST_BASIC should fail the conditional
+# dependency since BAR is set.
+# TEST_COMPLEX will fail dependency as it depends on both FOO and BAR
+# if either of those is selected.
+CONFIG_FOO=n
+CONFIG_BAR=y
+CONFIG_BAZ=y
diff --git a/scripts/kconfig/tests/conditional_dep/test_config3 b/scripts/kconfig/tests/conditional_dep/test_config3
new file mode 100644
index 000000000000..86304f3aa557
--- /dev/null
+++ b/scripts/kconfig/tests/conditional_dep/test_config3
@@ -0,0 +1,6 @@
+# If FOO is not selected, but BAR is also not selected, then TEST_BASIC
+# should pass since the dependency on FOO is conditional on BAR.
+# TEST_COMPLEX should be also set since neither FOO nor BAR are selected
+# so it has no dependencies.
+CONFIG_FOO=n
+CONFIG_BAR=n