[libc-commits] [libc] 81dfeb7 - [libc][locale] Fix nullptr argument handling in setlocale. (#229569)

[via libc-commits]

Author: Alexey Samsonov
Date: 2026-10-06T21:53:16Z
New Revision: 81dfeb7806617258f1a3b0fd859af3a7db49f6f0

URL: https://github.com/llvm/llvm-project/commit/81dfeb7806617258f1a3b0fd859af3a7db49f6f0
DIFF: https://github.com/llvm/llvm-project/commit/81dfeb7806617258f1a3b0fd859af3a7db49f6f0.diff

LOG: [libc][locale] Fix nullptr argument handling in setlocale. (#229569)

`setlocale` function should accept `nullptr` as a possible value for the
second argument - in this case the
locale is not modified but queried. Make sure to return `C` locale in
this case (the only one supported by LLVM-libc).

Expand the unit test to verify `setlocale` behavior.

Added: 
    

Modified: 
    libc/src/locale/newlocale.h
    libc/src/locale/setlocale.cpp
    libc/test/src/locale/CMakeLists.txt
    libc/test/src/locale/locale_test.cpp

Removed: 
    


################################################################################
diff  --git a/libc/src/locale/newlocale.h b/libc/src/locale/newlocale.h
index 07972fa384433c..211bbb19b9f8c7 100644
--- a/libc/src/locale/newlocale.h
+++ b/libc/src/locale/newlocale.h
@@ -1,13 +1,18 @@
-//===-- Implementation header for setlocale ---------------------*- C++ -*-===//
+//===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
+///
+/// \file
+/// Implementation header for newlocale.
+///
+//===----------------------------------------------------------------------===//
 
-#ifndef LLVM_LIBC_SRC_LOCALE_SETLOCALE_H
-#define LLVM_LIBC_SRC_LOCALE_SETLOCALE_H
+#ifndef LLVM_LIBC_SRC_LOCALE_NEWLOCALE_H
+#define LLVM_LIBC_SRC_LOCALE_NEWLOCALE_H
 
 #include "hdr/types/locale_t.h"
 #include "src/__support/macros/config.h"
@@ -18,4 +23,4 @@ locale_t newlocale(int category_mask, const char *locale_name, locale_t base);
 
 } // namespace LIBC_NAMESPACE_DECL
 
-#endif // LLVM_LIBC_SRC_LOCALE_SETLOCALE_H
+#endif // LLVM_LIBC_SRC_LOCALE_NEWLOCALE_H

diff  --git a/libc/src/locale/setlocale.cpp b/libc/src/locale/setlocale.cpp
index 2dec497ce051a4..bdc311eead2a7e 100644
--- a/libc/src/locale/setlocale.cpp
+++ b/libc/src/locale/setlocale.cpp
@@ -1,10 +1,15 @@
-//===-- Implementation of setlocale ---------------------------------------===//
+//===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
+///
+/// \file
+/// Implementation of setlocale.
+///
+//===----------------------------------------------------------------------===//
 
 #include "src/locale/setlocale.h"
 #include "hdr/locale_macros.h"
@@ -15,10 +20,15 @@
 namespace LIBC_NAMESPACE_DECL {
 
 LLVM_LIBC_FUNCTION(char *, setlocale, (int category, const char *locale_name)) {
-  cpp::string_view name(locale_name);
-  if (category > LC_ALL || (!name.empty() && name != "C"))
+  if (category > LC_ALL)
     return nullptr;
 
+  if (locale_name != nullptr) {
+    cpp::string_view name(locale_name);
+    if (!name.empty() && name != "C")
+      return nullptr;
+  }
+
   static char locale_str[] = "C";
   return locale_str;
 }

diff  --git a/libc/test/src/locale/CMakeLists.txt b/libc/test/src/locale/CMakeLists.txt
index 5032ce9c324e23..2a50e2ed87d1b9 100644
--- a/libc/test/src/locale/CMakeLists.txt
+++ b/libc/test/src/locale/CMakeLists.txt
@@ -9,6 +9,7 @@ add_libc_test(
   DEPENDS
     libc.hdr.locale_macros
     libc.src.locale.newlocale
+    libc.src.locale.setlocale
     libc.src.locale.uselocale
     libc.src.locale.freelocale
 )

diff  --git a/libc/test/src/locale/locale_test.cpp b/libc/test/src/locale/locale_test.cpp
index d19e2605fca375..a55ad85006260c 100644
--- a/libc/test/src/locale/locale_test.cpp
+++ b/libc/test/src/locale/locale_test.cpp
@@ -1,14 +1,20 @@
-//===-- Unittests for locale ----------------------------------------------===//
+//===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
+///
+/// \file
+/// Unittests for locale.
+///
+//===----------------------------------------------------------------------===//
 
 #include "hdr/locale_macros.h"
 #include "src/locale/freelocale.h"
 #include "src/locale/newlocale.h"
+#include "src/locale/setlocale.h"
 #include "src/locale/uselocale.h"
 #include "test/UnitTest/Test.h"
 
@@ -45,3 +51,20 @@ TEST(LlvmLibcLocale, NewLocaleValidation) {
   loc = LIBC_NAMESPACE::newlocale(LC_ALL_MASK, "does-not-exist", nullptr);
   EXPECT_EQ(loc, static_cast<locale_t>(nullptr));
 }
+
+TEST(LlvmLibcLocale, SetLocale) {
+  // Setting a "C" or default locale.
+  EXPECT_STREQ(LIBC_NAMESPACE::setlocale(LC_ALL, "C"), "C");
+  EXPECT_STREQ(LIBC_NAMESPACE::setlocale(LC_CTYPE, ""), "C");
+  // Querying the current locale.
+  EXPECT_STREQ(LIBC_NAMESPACE::setlocale(LC_ALL, nullptr), "C");
+  EXPECT_STREQ(LIBC_NAMESPACE::setlocale(LC_NUMERIC, nullptr), "C");
+
+  // Unsupporter categories or non-C locales.
+  EXPECT_EQ(LIBC_NAMESPACE::setlocale(LC_ALL + 1, "C"),
+            static_cast<char *>(nullptr));
+  EXPECT_EQ(LIBC_NAMESPACE::setlocale(LC_ALL + 1, nullptr),
+            static_cast<char *>(nullptr));
+  EXPECT_EQ(LIBC_NAMESPACE::setlocale(LC_ALL, "does-not-exist"),
+            static_cast<char *>(nullptr));
+}