added errno handling

Author: uzairnawaz

libc/src/wchar/CMakeLists.txt

@@ -58,6 +58,7 @@ add_entrypoint_object(
     libc.hdr.types.wchar_t
     libc.src.__support.wchar.wcrtomb
     libc.src.__support.wchar.mbstate
+    libc.src.__support.libc_errno
 )
 
 add_entrypoint_object(

libc/src/wchar/wctomb.cpp

@@ -10,6 +10,7 @@
 
 #include "hdr/types/wchar_t.h"
 #include "src/__support/common.h"
+#include "src/__support/libc_errno.h"
 #include "src/__support/macros/config.h"
 #include "src/__support/wchar/mbstate.h"
 #include "src/__support/wchar/wcrtomb.h"
@@ -23,8 +24,10 @@ LLVM_LIBC_FUNCTION(int, wctomb, (char *s, wchar_t wc)) {
 
   auto result = internal::wcrtomb(s, wc, &internal_mbstate);
 
-  if (!result.has_value()) // invalid wide character
+  if (!result.has_value()) { // invalid wide character
+    libc_errno = EILSEQ;
     return -1;
+  }
 
   return static_cast<int>(result.value());
 }

libc/test/src/wchar/wctomb_test.cpp

@@ -7,9 +7,13 @@
 //===----------------------------------------------------------------------===//
 
 #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];
@@ -65,4 +69,5 @@ TEST(LlvmLibcWCToMBTest, InvalidWchar) {
   char mb[4];
   int cnt = LIBC_NAMESPACE::wctomb(mb, wc);
   ASSERT_EQ(cnt, -1);
+  ASSERT_ERRNO_EQ(EILSEQ);
 }