[libc] Implemented wcrtomb internal function and public libc function (#144596)

Implemented internal wcrtomb function using the CharacterConverter class
public libc function calls this internal function to perform the
conversion

libc/test/src/wchar/CMakeLists.txt

@@ -47,6 +47,20 @@ add_libc_test(
     libc.src.wchar.wctob
 )
 
+add_libc_test(
+  wcrtomb_test
+  SUITE
+    libc_wchar_unittests
+  SRCS
+    wcrtomb_test.cpp
+  DEPENDS
+    libc.src.wchar.wcrtomb
+    libc.src.string.memset
+    libc.hdr.types.wchar_t
+    libc.hdr.types.mbstate_t
+    libc.src.__support.libc_errno
+)
+
 add_libc_test(
   wmemset_test 
   SUITE

libc/test/src/wchar/wcrtomb_test.cpp

@@ -0,0 +1,93 @@
+//===-- Unittests for wcrtomb --------------------------------------------===//
+//
+// 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/mbstate_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/libc_errno.h"
+#include "src/string/memset.h"
+#include "src/wchar/wcrtomb.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcWCRToMBTest, OneByte) {
+  mbstate_t state;
+  LIBC_NAMESPACE::memset(&state, 0, sizeof(mbstate_t));
+  wchar_t wc = L'U';
+  char mb[4];
+  size_t cnt = LIBC_NAMESPACE::wcrtomb(mb, wc, &state);
+  ASSERT_EQ(cnt, static_cast<size_t>(1));
+  ASSERT_EQ(mb[0], 'U');
+}
+
+TEST(LlvmLibcWCRToMBTest, TwoByte) {
+  mbstate_t state;
+  LIBC_NAMESPACE::memset(&state, 0, sizeof(mbstate_t));
+  // testing utf32: 0xff -> utf8: 0xc3 0xbf
+  wchar_t wc = 0xff;
+  char mb[4];
+  size_t cnt = LIBC_NAMESPACE::wcrtomb(mb, wc, &state);
+  ASSERT_EQ(cnt, static_cast<size_t>(2));
+  ASSERT_EQ(mb[0], static_cast<char>(0xc3));
+  ASSERT_EQ(mb[1], static_cast<char>(0xbf));
+}
+
+TEST(LlvmLibcWCRToMBTest, ThreeByte) {
+  mbstate_t state;
+  LIBC_NAMESPACE::memset(&state, 0, sizeof(mbstate_t));
+  // testing utf32: 0xac15 -> utf8: 0xea 0xb0 0x95
+  wchar_t wc = 0xac15;
+  char mb[4];
+  size_t cnt = LIBC_NAMESPACE::wcrtomb(mb, wc, &state);
+  ASSERT_EQ(cnt, static_cast<size_t>(3));
+  ASSERT_EQ(mb[0], static_cast<char>(0xea));
+  ASSERT_EQ(mb[1], static_cast<char>(0xb0));
+  ASSERT_EQ(mb[2], static_cast<char>(0x95));
+}
+
+TEST(LlvmLibcWCRToMBTest, FourByte) {
+  mbstate_t state;
+  LIBC_NAMESPACE::memset(&state, 0, sizeof(mbstate_t));
+  // testing utf32: 0x1f921 -> utf8: 0xf0 0x9f 0xa4 0xa1
+  wchar_t wc = 0x1f921;
+  char mb[4];
+  size_t cnt = LIBC_NAMESPACE::wcrtomb(mb, wc, &state);
+  ASSERT_EQ(cnt, static_cast<size_t>(4));
+  ASSERT_EQ(mb[0], static_cast<char>(0xf0));
+  ASSERT_EQ(mb[1], static_cast<char>(0x9f));
+  ASSERT_EQ(mb[2], static_cast<char>(0xa4));
+  ASSERT_EQ(mb[3], static_cast<char>(0xa1));
+}
+
+TEST(LlvmLibcWCRToMBTest, NullString) {
+  mbstate_t state;
+  LIBC_NAMESPACE::memset(&state, 0, sizeof(mbstate_t));
+  wchar_t wc = L'A';
+  char mb[4];
+
+  // should be equivalent to the call wcrtomb(buf, L'\0', state)
+  size_t cnt1 = LIBC_NAMESPACE::wcrtomb(nullptr, wc, &state);
+  size_t cnt2 = LIBC_NAMESPACE::wcrtomb(mb, L'\0', &state);
+
+  ASSERT_EQ(cnt1, cnt2);
+}
+
+TEST(LlvmLibcWCRToMBTest, NullState) {
+  wchar_t wc = L'A';
+  char mb[4];
+  size_t cnt = LIBC_NAMESPACE::wcrtomb(mb, wc, nullptr);
+  ASSERT_EQ(cnt, static_cast<size_t>(1));
+}
+
+TEST(LlvmLibcWCRToMBTest, InvalidWchar) {
+  mbstate_t state;
+  LIBC_NAMESPACE::memset(&state, 0, sizeof(mbstate_t));
+  wchar_t wc = 0x12ffff;
+  char mb[4];
+  size_t cnt = LIBC_NAMESPACE::wcrtomb(mb, wc, &state);
+  ASSERT_EQ(cnt, static_cast<size_t>(-1));
+  ASSERT_EQ(static_cast<int>(libc_errno), EILSEQ);
+}