[libc] Implemented wctomb (#145554)

Implemented wctomb by calling internal wcrtomb function
Added tests

libc/test/src/wchar/CMakeLists.txt

@@ -74,6 +74,17 @@ add_libc_test(
     libc.src.__support.libc_errno
 )
 
+add_libc_test(
+  wctomb_test
+  SUITE
+    libc_wchar_unittests
+  SRCS
+    wctomb_test.cpp
+  DEPENDS
+    libc.src.wchar.wctomb
+    libc.hdr.types.wchar_t
+)
+
 add_libc_test(
   wmemset_test 
   SUITE

libc/test/src/wchar/wctomb_test.cpp

@@ -0,0 +1,73 @@
+//===-- Unittests for wctomb ----------------------------------------------===//
+//
+// 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/__support/libc_errno.h"
+#include "src/wchar/wctomb.h"
+#include "test/UnitTest/ErrnoCheckingTest.h"
+#include "test/UnitTest/Test.h"
+
+using LlvmLibcWCToMBTest = LIBC_NAMESPACE::testing::ErrnoCheckingTest;
+
+TEST(LlvmLibcWCToMBTest, OneByte) {
+  wchar_t wc = L'U';
+  char mb[4];
+  int cnt = LIBC_NAMESPACE::wctomb(mb, wc);
+  ASSERT_EQ(cnt, 1);
+  ASSERT_EQ(mb[0], 'U');
+}
+
+TEST(LlvmLibcWCToMBTest, TwoByte) {
+  // testing utf32: 0xff -> utf8: 0xc3 0xbf
+  wchar_t wc = 0xff;
+  char mb[4];
+  int cnt = LIBC_NAMESPACE::wctomb(mb, wc);
+  ASSERT_EQ(cnt, 2);
+  ASSERT_EQ(mb[0], static_cast<char>(0xc3));
+  ASSERT_EQ(mb[1], static_cast<char>(0xbf));
+}
+
+TEST(LlvmLibcWCToMBTest, ThreeByte) {
+  // testing utf32: 0xac15 -> utf8: 0xea 0xb0 0x95
+  wchar_t wc = 0xac15;
+  char mb[4];
+  int cnt = LIBC_NAMESPACE::wctomb(mb, wc);
+  ASSERT_EQ(cnt, 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(LlvmLibcWCToMBTest, FourByte) {
+  // testing utf32: 0x1f921 -> utf8: 0xf0 0x9f 0xa4 0xa1
+  wchar_t wc = 0x1f921;
+  char mb[4];
+  int cnt = LIBC_NAMESPACE::wctomb(mb, wc);
+  ASSERT_EQ(cnt, 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(LlvmLibcWCToMBTest, NullString) {
+  wchar_t wc = L'A';
+
+  int cnt = LIBC_NAMESPACE::wctomb(nullptr, wc);
+
+  // no state-dependent encoding
+  ASSERT_EQ(cnt, 0);
+}
+
+TEST(LlvmLibcWCToMBTest, InvalidWchar) {
+  wchar_t wc = 0x12ffff;
+  char mb[4];
+  int cnt = LIBC_NAMESPACE::wctomb(mb, wc);
+  ASSERT_EQ(cnt, -1);
+  ASSERT_ERRNO_EQ(EILSEQ);
+}