[libc] Move mbtowc, mbstowcs and inverse functions to stdlib.h (#168455)

These functions should be declared in `stdlib.h`, not `wchar.h`, as
confusing as it is. Move them to the proper header file and matching
directories in src/ and test/ trees.

This was discovered while testing libc++ build against llvm-libc, which
re-declares functions like mbtowc in std-namespace in `<cstdlib>`
header, and then uses those functions in its locale implementation.

9 files changed, 297 insertions, 0 deletions

diff --git a/libc/src/stdlib/CMakeLists.txt b/libc/src/stdlib/CMakeLists.txt
index 1ccdcc8bec14..62da469f0eb9 100644
--- a/libc/src/stdlib/CMakeLists.txt
+++ b/libc/src/stdlib/CMakeLists.txt
@@ -368,6 +368,65 @@ add_entrypoint_object(
     libc.hdr.types.size_t
 )
 
+add_entrypoint_object(
+  mbtowc
+  SRCS
+    mbtowc.cpp
+  HDRS
+    mbtowc.h
+  DEPENDS
+    libc.hdr.types.size_t
+    libc.hdr.types.wchar_t
+    libc.src.__support.common
+    libc.src.__support.macros.config
+    libc.src.__support.libc_errno
+    libc.src.__support.wchar.mbrtowc
+    libc.src.__support.wchar.mbstate
+)
+
+add_entrypoint_object(
+  mbstowcs
+  SRCS
+    mbstowcs.cpp
+  HDRS
+    mbstowcs.h
+  DEPENDS
+    libc.hdr.types.size_t
+    libc.hdr.types.wchar_t
+    libc.src.__support.common
+    libc.src.__support.macros.config
+    libc.src.__support.macros.null_check
+    libc.src.__support.libc_errno
+    libc.src.__support.wchar.mbstate
+    libc.src.__support.wchar.mbsnrtowcs
+)
+
+add_entrypoint_object(
+  wctomb
+  SRCS
+    wctomb.cpp
+  HDRS
+    wctomb.h
+  DEPENDS
+    libc.hdr.types.wchar_t
+    libc.src.__support.wchar.wcrtomb
+    libc.src.__support.wchar.mbstate
+    libc.src.__support.libc_errno
+)
+
+add_entrypoint_object(
+  wcstombs
+  SRCS
+    wcstombs.cpp
+  HDRS
+    wcstombs.h
+  DEPENDS
+    libc.hdr.types.wchar_t
+    libc.src.__support.wchar.mbstate
+    libc.src.__support.wchar.wcsnrtombs
+    libc.src.__support.libc_errno
+)
+
 if(NOT LIBC_TARGET_OS_IS_BAREMETAL AND NOT LIBC_TARGET_OS_IS_GPU)
   if(LLVM_LIBC_INCLUDE_SCUDO)
     set(SCUDO_DEPS "")
diff --git a/libc/src/stdlib/mbstowcs.cpp b/libc/src/stdlib/mbstowcs.cpp
new file mode 100644
index 000000000000..6d283ea46e3b
--- /dev/null
+++ b/libc/src/stdlib/mbstowcs.cpp
@@ -0,0 +1,40 @@
+//===-- Implementation of mbstowcs ----------------------------------------===//
+//
+// 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 "src/stdlib/mbstowcs.h"
+
+#include "hdr/types/size_t.h"
+#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/macros/null_check.h"
+#include "src/__support/wchar/mbsnrtowcs.h"
+#include "src/__support/wchar/mbstate.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(size_t, mbstowcs,
+                   (wchar_t *__restrict pwcs, const char *__restrict s,
+                    size_t n)) {
+  LIBC_CRASH_ON_NULLPTR(s);
+  // If destination is null, ignore n
+  n = pwcs == nullptr ? SIZE_MAX : n;
+  static internal::mbstate internal_mbstate;
+  const char *temp = s;
+  auto ret = internal::mbsnrtowcs(pwcs, &temp, SIZE_MAX, n, &internal_mbstate);
+
+  if (!ret.has_value()) {
+    // Encoding failure
+    libc_errno = ret.error();
+    return -1;
+  }
+  return ret.value();
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/stdlib/mbstowcs.h b/libc/src/stdlib/mbstowcs.h
new file mode 100644
index 000000000000..90f8195a39ec
--- /dev/null
+++ b/libc/src/stdlib/mbstowcs.h
@@ -0,0 +1,22 @@
+//===-- Implementation header for mbstowcs --------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDLIB_MBSTOWCS_H
+#define LLVM_LIBC_SRC_STDLIB_MBSTOWCS_H
+
+#include "hdr/types/size_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+size_t mbstowcs(wchar_t *__restrict pwcs, const char *__restrict s, size_t n);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_STDLIB_MBSTOWCS_H
diff --git a/libc/src/stdlib/mbtowc.cpp b/libc/src/stdlib/mbtowc.cpp
new file mode 100644
index 000000000000..5f482463f471
--- /dev/null
+++ b/libc/src/stdlib/mbtowc.cpp
@@ -0,0 +1,37 @@
+//===-- Implementation of mbtowc -----------------------------------------===//
+//
+// 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 "src/stdlib/mbtowc.h"
+
+#include "hdr/types/size_t.h"
+#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/mbrtowc.h"
+#include "src/__support/wchar/mbstate.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, mbtowc,
+                   (wchar_t *__restrict pwc, const char *__restrict s,
+                    size_t n)) {
+  // returns 0 since UTF-8 encoding is not state-dependent
+  if (s == nullptr)
+    return 0;
+  internal::mbstate internal_mbstate;
+  auto ret = internal::mbrtowc(pwc, s, n, &internal_mbstate);
+  if (!ret.has_value() || static_cast<int>(ret.value()) == -2) {
+    // Encoding failure
+    libc_errno = EILSEQ;
+    return -1;
+  }
+  return static_cast<int>(ret.value());
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/stdlib/mbtowc.h b/libc/src/stdlib/mbtowc.h
new file mode 100644
index 000000000000..acd85cb77ba7
--- /dev/null
+++ b/libc/src/stdlib/mbtowc.h
@@ -0,0 +1,22 @@
+//===-- Implementation header for mbtowc ---------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDLIB_MBTOWC_H
+#define LLVM_LIBC_SRC_STDLIB_MBTOWC_H
+
+#include "hdr/types/size_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int mbtowc(wchar_t *__restrict pwc, const char *__restrict s, size_t n);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_STDLIB_MBTOWC_H
diff --git a/libc/src/stdlib/wcstombs.cpp b/libc/src/stdlib/wcstombs.cpp
new file mode 100644
index 000000000000..712af958456d
--- /dev/null
+++ b/libc/src/stdlib/wcstombs.cpp
@@ -0,0 +1,38 @@
+//===-- Implementation of wcstombs ----------------------------------------===//
+//
+// 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 "src/stdlib/wcstombs.h"
+
+#include "hdr/types/char32_t.h"
+#include "hdr/types/size_t.h"
+#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/wcsnrtombs.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(size_t, wcstombs,
+                   (char *__restrict s, const wchar_t *__restrict wcs,
+                    size_t n)) {
+  LIBC_CRASH_ON_NULLPTR(wcs);
+  static internal::mbstate internal_mbstate;
+  const wchar_t *wcs_ptr_copy = wcs;
+  auto result =
+      internal::wcsnrtombs(s, &wcs_ptr_copy, SIZE_MAX, n, &internal_mbstate);
+  if (!result.has_value()) {
+    libc_errno = result.error();
+    return -1;
+  }
+
+  return result.value();
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/stdlib/wcstombs.h b/libc/src/stdlib/wcstombs.h
new file mode 100644
index 000000000000..39515431098c
--- /dev/null
+++ b/libc/src/stdlib/wcstombs.h
@@ -0,0 +1,22 @@
+//===-- Implementation header for wcstombs --------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDLIB_WCSTOMBS_H
+#define LLVM_LIBC_SRC_STDLIB_WCSTOMBS_H
+
+#include "hdr/types/size_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+size_t wcstombs(char *__restrict s, const wchar_t *__restrict pwcs, size_t n);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_STDLIB_WCSTOMBS_H
diff --git a/libc/src/stdlib/wctomb.cpp b/libc/src/stdlib/wctomb.cpp
new file mode 100644
index 000000000000..0ca1a84cd923
--- /dev/null
+++ b/libc/src/stdlib/wctomb.cpp
@@ -0,0 +1,35 @@
+//===-- Implementation of 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 "src/stdlib/wctomb.h"
+
+#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"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, wctomb, (char *s, wchar_t wc)) {
+  static internal::mbstate internal_mbstate;
+  if (s == nullptr)
+    return 0;
+
+  auto result = internal::wcrtomb(s, wc, &internal_mbstate);
+
+  if (!result.has_value()) { // invalid wide character
+    libc_errno = EILSEQ;
+    return -1;
+  }
+
+  return static_cast<int>(result.value());
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/stdlib/wctomb.h b/libc/src/stdlib/wctomb.h
new file mode 100644
index 000000000000..90afa31d9e70
--- /dev/null
+++ b/libc/src/stdlib/wctomb.h
@@ -0,0 +1,22 @@
+//===-- Implementation header for wctomb ------------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDLIB_WCTOMB_H
+#define LLVM_LIBC_SRC_STDLIB_WCTOMB_H
+
+#include "hdr/types/mbstate_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int wctomb(char *s, wchar_t wc);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_STDLIB_WCTOMB_H