[libc] Implemented wcsrchr (#142436)

fixes #124347 
Implemented wcsrchr and added tests

libc/test/src/wchar/CMakeLists.txt

@@ -75,6 +75,16 @@ add_libc_test(
     libc.src.wchar.wcspbrk
 )
 
+add_libc_test(
+  wcsrchr_test
+  SUITE
+    libc_wchar_unittests
+  SRCS
+    wcsrchr_test.cpp
+  DEPENDS
+    libc.src.wchar.wcsrchr
+)
+
 add_libc_test(
   wcsspn_test
   SUITE

libc/test/src/wchar/wcsrchr_test.cpp

@@ -0,0 +1,68 @@
+//===-- Unittests for wcsrchr ---------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "hdr/types/wchar_t.h"
+#include "src/wchar/wcsrchr.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcWCSRChrTest, FindsFirstCharacter) {
+  // Should return pointer to original string since 'a' is the first character.
+  const wchar_t *src = L"abcde";
+  ASSERT_EQ(LIBC_NAMESPACE::wcsrchr(src, L'a'), src);
+}
+
+TEST(LlvmLibcWCSRChrTest, FindsMiddleCharacter) {
+  // Should return pointer to 'c'.
+  const wchar_t *src = L"abcde";
+  ASSERT_EQ(LIBC_NAMESPACE::wcsrchr(src, L'c'), (src + 2));
+}
+
+TEST(LlvmLibcWCSRChrTest, FindsLastCharacterThatIsNotNullTerminator) {
+  // Should return pointer to 'e'.
+  const wchar_t *src = L"abcde";
+  ASSERT_EQ(LIBC_NAMESPACE::wcsrchr(src, L'e'), (src + 4));
+}
+
+TEST(LlvmLibcWCSRChrTest, FindsNullTerminator) {
+  // Should return pointer to null terminator.
+  const wchar_t *src = L"abcde";
+  ASSERT_EQ(LIBC_NAMESPACE::wcsrchr(src, L'\0'), (src + 5));
+}
+
+TEST(LlvmLibcWCSRChrTest, CharacterNotWithinStringShouldReturnNullptr) {
+  // Since 'z' is not within the string, should return nullptr.
+  const wchar_t *src = L"abcde";
+  ASSERT_EQ(LIBC_NAMESPACE::wcsrchr(src, L'z'), nullptr);
+}
+
+TEST(LlvmLibcWCSRChrTest, ShouldFindLastOfDuplicates) {
+  // Should return pointer to the last '1'.
+  const wchar_t *src = L"abc1def1ghi";
+  ASSERT_EQ((int)(LIBC_NAMESPACE::wcsrchr(src, L'1') - src), 7);
+
+  // Should return pointer to the last 'X'
+  const wchar_t *dups = L"XXXXX";
+  ASSERT_EQ(LIBC_NAMESPACE::wcsrchr(dups, L'X'), dups + 4);
+}
+
+TEST(LlvmLibcWCSRChrTest, EmptyStringShouldOnlyMatchNullTerminator) {
+  // Null terminator should match
+  const wchar_t *src = L"";
+  ASSERT_EQ(src, LIBC_NAMESPACE::wcsrchr(src, L'\0'));
+  // All other characters should not match
+  ASSERT_EQ(LIBC_NAMESPACE::wcsrchr(src, L'Z'), nullptr);
+  ASSERT_EQ(LIBC_NAMESPACE::wcsrchr(src, L'3'), nullptr);
+  ASSERT_EQ(LIBC_NAMESPACE::wcsrchr(src, L'*'), nullptr);
+}
+
+#if defined(LIBC_ADD_NULL_CHECKS) && !defined(LIBC_HAS_SANITIZER)
+TEST(LlvmLibcWCSRChrTest, NullptrCrash) {
+  // Passing in a nullptr should crash the program.
+  EXPECT_DEATH([] { LIBC_NAMESPACE::wcsrchr(nullptr, L'a'); }, WITH_SIGNAL(-1));
+}
+#endif // LIBC_HAS_ADDRESS_SANITIZER