kconfig: Error out on duplicated kconfig inclusion

Let kconfig exit with error on duplicated Kconfig file inclusion.

Repeated inclusion of Kbuild files are considered bad-practise with
regard to maintenance; and Kconfig language is rich enough that there
should be no need for that.

If repeated inclusion of Kconfig files is detected, error out with
messages like:

    Kconfig.inc1:4: error: repeated inclusion of Kconfig.inc3
    Kconfig.inc2:3: note: location of first inclusion of Kconfig.inc3

While commit f094f8a1b2 ("kconfig: allow multiple inclusion of the
same file") introduced detection of recursive inclusions of Kconfig
files, it explicitly allowed repeated inclusions, unfortunately w/o
reasoning.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Closes: https://lore.kernel.org/all/CAHk-=wj03hLzK2D=+OYmjgcmGM+XYymp8GyaEs=C0=rXG2nb7w@mail.gmail.com/
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Link: https://patch.msgid.link/20260220-kconfig-error-out-on-duplicated-inclusion-v1-1-be78aa241a53@kernel.org
Signed-off-by: Nicolas Schier <nsc@kernel.org>

scripts/kconfig/lexer.l

@@ -402,7 +402,7 @@ void zconf_initscan(const char *name)
 		exit(1);
 	}
 
-	cur_filename = file_lookup(name);
+	cur_filename = file_lookup(name, NULL, 0);
 	yylineno = 1;
 }
 
@@ -443,7 +443,7 @@ void zconf_nextfile(const char *name)
 	}
 
 	yylineno = 1;
-	cur_filename = file_lookup(name);
+	cur_filename = file_lookup(name, cur_filename, cur_lineno);
 }
 
 static void zconf_endfile(void)

scripts/kconfig/lkc.h

@@ -51,7 +51,8 @@ static inline void xfwrite(const void *str, size_t len, size_t count, FILE *out)
 }
 
 /* util.c */
-const char *file_lookup(const char *name);
+const char *file_lookup(const char *name,
+			const char *parent_name, int parent_lineno);
 
 /* lexer.l */
 int yylex(void);

scripts/kconfig/tests/err_repeated_inc/Kconfig

@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+source "Kconfig.inc1"

scripts/kconfig/tests/err_repeated_inc/Kconfig.inc1

@@ -0,0 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+source "Kconfig.inc2"
+source "Kconfig.inc3"

scripts/kconfig/tests/err_repeated_inc/Kconfig.inc2

@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+source "Kconfig.inc3"

scripts/kconfig/tests/err_repeated_inc/Kconfig.inc3

@@ -0,0 +1 @@
+# SPDX-License-Identifier: GPL-2.0-only

scripts/kconfig/tests/err_repeated_inc/__init__.py

@@ -0,0 +1,10 @@
+# SPDX-License-Identifier: GPL-2.0
+"""
+Detect repeated inclusion error.
+
+If repeated inclusion is detected, it should fail with error message.
+"""
+
+def test(conf):
+    assert conf.oldaskconfig() != 0
+    assert conf.stderr_contains('expected_stderr')

scripts/kconfig/tests/err_repeated_inc/expected_stderr

@@ -0,0 +1,2 @@
+Kconfig.inc1:4: error: Repeated inclusion of Kconfig.inc3
+Kconfig.inc2:3: note: Location of first inclusion of Kconfig.inc3

scripts/kconfig/util.c

@@ -18,25 +18,50 @@ static HASHTABLE_DEFINE(file_hashtable, 1U << 11);
 
 struct file {
 	struct hlist_node node;
+	struct {
+		const char *name;
+		int lineno;
+	} parent;
 	char name[];
 };
 
-/* file already present in list? If not add it */
-const char *file_lookup(const char *name)
+static void die_duplicated_include(struct file *file,
+				   const char *parent, int lineno)
 {
+	fprintf(stderr,
+		"%s:%d: error: repeated inclusion of %s\n"
+		"%s:%d: note: location of first inclusion of %s\n",
+		parent, lineno, file->name,
+		file->parent.name, file->parent.lineno, file->name);
+	exit(1);
+}
+
+/* file already present in list? If not add it */
+const char *file_lookup(const char *name,
+			const char *parent_name, int parent_lineno)
+{
+	const char *parent = NULL;
 	struct file *file;
 	size_t len;
 	int hash = hash_str(name);
 
+	if (parent_name)
+		parent = file_lookup(parent_name, NULL, 0);
+
 	hash_for_each_possible(file_hashtable, file, node, hash)
-		if (!strcmp(name, file->name))
-			return file->name;
+		if (!strcmp(name, file->name)) {
+			if (!parent_name)
+				return file->name;
+			die_duplicated_include(file, parent, parent_lineno);
+		}
 
 	len = strlen(name);
 	file = xmalloc(sizeof(*file) + len + 1);
 	memset(file, 0, sizeof(*file));
 	memcpy(file->name, name, len);
 	file->name[len] = '\0';
+	file->parent.name = parent;
+	file->parent.lineno = parent_lineno;
 
 	hash_add(file_hashtable, &file->node, hash);