[PATCH] kconfig: error out for recursive range

[Julian Braha]

Currently, it is possible to create recursive ranges with Kconfig, such as:

config C
  int "Enable C"
  default 1
  range A B

config A
  int "Enable A"
  default 2
  range B C

config B
  int "Enable B"
  default 3
  range A C

The current outcome of this example above, is that all 3 options are set to 2.
There is currently no warning or error if a user attempts this.

Several attributes are already checked for recursion, including 'depends on',
'select', and 'imply', and we can extend this to 'range' for numeric options
(int and hex types).

Recursive ranges are currently not used anywhere in the tree, so it is already
safe to make this a hard error.

Assisted-by: Codex:gpt-5.6-sol
Signed-off-by: Julian Braha <julianbraha@xxxxxxxxx>
---
 scripts/kconfig/symbol.c                      |  5 +++-
 .../kconfig/tests/err_recursive_dep/Kconfig   | 24 +++++++++++++++++++
 .../tests/err_recursive_dep/expected_stderr   | 13 ++++++++++
 3 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/scripts/kconfig/symbol.c b/scripts/kconfig/symbol.c
index 7e81b3676ee9..e82f330fb8ee 100644
--- a/scripts/kconfig/symbol.c
+++ b/scripts/kconfig/symbol.c
@@ -1196,6 +1196,7 @@ static struct symbol *sym_check_expr_deps(const struct expr *e)
 	case E_GTH:
 	case E_LEQ:
 	case E_LTH:
+	case E_RANGE:
 	case E_UNEQUAL:
 		sym = sym_check_deps(e->left.sym);
 		if (sym)
@@ -1243,7 +1244,9 @@ static struct symbol *sym_check_sym_deps(struct symbol *sym)
 		sym2 = sym_check_expr_deps(prop->visible.expr);
 		if (sym2)
 			break;
-		if (prop->type != P_DEFAULT || sym_is_choice(sym))
+		if (sym_is_choice(sym))
+			continue;
+		if (prop->type != P_DEFAULT && prop->type != P_RANGE)
 			continue;
 		stack.expr = &prop->expr;
 		sym2 = sym_check_expr_deps(prop->expr);
diff --git a/scripts/kconfig/tests/err_recursive_dep/Kconfig b/scripts/kconfig/tests/err_recursive_dep/Kconfig
index ebdb3ffd8717..bd1ff92bcab2 100644
--- a/scripts/kconfig/tests/err_recursive_dep/Kconfig
+++ b/scripts/kconfig/tests/err_recursive_dep/Kconfig
@@ -61,3 +61,27 @@ config G
 	bool "G"
 
 endmenu
+
+# depends on and range
+
+config H1
+	int
+	depends on H2 < H3
+
+config H2
+	int
+	range H3 H1
+
+config H3
+	int
+	range H1 H2
+
+# range
+
+config I1
+	int
+	range I2 I2
+
+config I2
+	int
+	range I1 I1
diff --git a/scripts/kconfig/tests/err_recursive_dep/expected_stderr b/scripts/kconfig/tests/err_recursive_dep/expected_stderr
index fc2e860af082..08f843087678 100644
--- a/scripts/kconfig/tests/err_recursive_dep/expected_stderr
+++ b/scripts/kconfig/tests/err_recursive_dep/expected_stderr
@@ -36,3 +36,16 @@ error: recursive dependency detected!
 	symbol G depends on G
 For a resolution refer to Documentation/kbuild/kconfig-language.rst
 subsection "Kconfig recursive dependency limitations"
+
+error: recursive dependency detected!
+	symbol H1 depends on H2
+	symbol H2 range value contains H3
+	symbol H3 range value contains H1
+For a resolution refer to Documentation/kbuild/kconfig-language.rst
+subsection "Kconfig recursive dependency limitations"
+
+error: recursive dependency detected!
+	symbol I1 range value contains I2
+	symbol I2 range value contains I1
+For a resolution refer to Documentation/kbuild/kconfig-language.rst
+subsection "Kconfig recursive dependency limitations"
-- 
2.55.0