[libc++] Adds more forward declaration headers.

[Mordante]

Summary

The module validation script of D144994 validate whether the contents of
an include match its module. An include is the set of files matching the
pattern:

• foo
• foo/*.
• __fwd/foo.h

Several declarations of the stream headers are in the header iosfwd.
This gives issue using the validation script. Adding iosfwd to the set
of matching files gives too many declarations. For example when
validating the fstream header it will pull in declarations of the
istream header. Instead if writing a set of filters the headers are
granularized into smaller headers containing the expected declarations.

[Mordante]

CI fixes.

[Mordante]

CI fixes.

[Mordante]

Trigger CI.

[Mordante]

Retrigger CI.

[Mordante]

Retrigger CI.

[Mordante]

CI fixes.

libcxx/include/CMakeLists.txt

set(files
   __functional/pointer_to_unary_function.h
   __functional/ranges_operations.h
   __functional/reference_wrapper.h
   __functional/unary_function.h
   __functional/unary_negate.h
   __functional/unwrap_ref.h
   __functional/weak_result_type.h
   __fwd/array.h
+  __fwd/fstream.h
   __fwd/get.h
   __fwd/hash.h
+  __fwd/ios.h
+  __fwd/istream.h
   __fwd/memory_resource.h
+  __fwd/ostream.h
   __fwd/pair.h
   __fwd/span.h
+  __fwd/sstream.h
+  __fwd/streambuf.h
   __fwd/string.h
   __fwd/string_view.h
   __fwd/subrange.h
   __fwd/tuple.h
   __hash_table
   __ios/fpos.h
   __iterator/access.h
   __iterator/advance.h

libcxx/include/__fwd/fstream.h

+//===----------------------------------------------------------------------===//
+//
+// 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 _LIBCPP___FWD_FSTREAM_H
+#define _LIBCPP___FWD_FSTREAM_H
+
+#include <__config>
+#include <__fwd/string.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _CharT, class _Traits = char_traits<_CharT> >
+    class _LIBCPP_TEMPLATE_VIS basic_filebuf;
+template <class _CharT, class _Traits = char_traits<_CharT> >
+    class _LIBCPP_TEMPLATE_VIS basic_ifstream;
+template <class _CharT, class _Traits = char_traits<_CharT> >
+    class _LIBCPP_TEMPLATE_VIS basic_ofstream;
+template <class _CharT, class _Traits = char_traits<_CharT> >
+    class _LIBCPP_TEMPLATE_VIS basic_fstream;
+
+typedef basic_filebuf<char>          filebuf;
+typedef basic_ifstream<char>         ifstream;
+typedef basic_ofstream<char>         ofstream;
+typedef basic_fstream<char>          fstream;
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+typedef basic_filebuf<wchar_t>       wfilebuf;
+typedef basic_ifstream<wchar_t>      wifstream;
+typedef basic_ofstream<wchar_t>      wofstream;
+typedef basic_fstream<wchar_t>       wfstream;
+#endif
+
+template <class _CharT, class _Traits>
+    class _LIBCPP_PREFERRED_NAME(filebuf) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wfilebuf)) basic_filebuf;
+template <class _CharT, class _Traits>
+    class _LIBCPP_PREFERRED_NAME(ifstream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wifstream)) basic_ifstream;
+template <class _CharT, class _Traits>
+    class _LIBCPP_PREFERRED_NAME(ofstream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wofstream)) basic_ofstream;
+template <class _CharT, class _Traits>
+    class _LIBCPP_PREFERRED_NAME(fstream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wfstream)) basic_fstream;
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FWD_FSTREAM_H

libcxx/include/__fwd/ios.h

+//===----------------------------------------------------------------------===//
+//
+// 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 _LIBCPP___FWD_IOS_H
+#define _LIBCPP___FWD_IOS_H
+
+#include <__config>
+#include <__fwd/string.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _CharT, class _Traits = char_traits<_CharT> >
+    class _LIBCPP_TEMPLATE_VIS basic_ios;
+
+typedef basic_ios<char>              ios;
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+typedef basic_ios<wchar_t>           wios;
+#endif
+
+template <class _CharT, class _Traits>
+    class _LIBCPP_PREFERRED_NAME(ios) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wios)) basic_ios;
+
+#if defined(_NEWLIB_VERSION)
+// On newlib, off_t is 'long int'
+typedef long int streamoff;         // for char_traits in <string>
+#else
+typedef long long streamoff;        // for char_traits in <string>
+#endif
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FWD_IOS_H

libcxx/include/__fwd/istream.h

+//===----------------------------------------------------------------------===//
+//
+// 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 _LIBCPP___FWD_ISTREAM_H
+#define _LIBCPP___FWD_ISTREAM_H
+
+#include <__config>
+#include <__fwd/string.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _CharT, class _Traits = char_traits<_CharT> >
+    class _LIBCPP_TEMPLATE_VIS basic_istream;
+
+template <class _CharT, class _Traits = char_traits<_CharT> >
+    class _LIBCPP_TEMPLATE_VIS basic_iostream;
+
+typedef basic_istream<char>          istream;
+typedef basic_iostream<char>         iostream;
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+typedef basic_istream<wchar_t>       wistream;
+typedef basic_iostream<wchar_t>      wiostream;
+#endif
+
+template <class _CharT, class _Traits>
+    class _LIBCPP_PREFERRED_NAME(istream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wistream)) basic_istream;
+
+template <class _CharT, class _Traits>
+    class _LIBCPP_PREFERRED_NAME(iostream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wiostream)) basic_iostream;
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FWD_ISTREAM_H

libcxx/include/__fwd/ostream.h

+//===----------------------------------------------------------------------===//
+//
+// 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 _LIBCPP___FWD_OSTREAM_H
+#define _LIBCPP___FWD_OSTREAM_H
+
+#include <__config>
+#include <__fwd/string.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _CharT, class _Traits = char_traits<_CharT> >
+    class _LIBCPP_TEMPLATE_VIS basic_ostream;
+
+typedef basic_ostream<char>          ostream;
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+typedef basic_ostream<wchar_t>       wostream;
+#endif
+
+template <class _CharT, class _Traits>
+    class _LIBCPP_PREFERRED_NAME(ostream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wostream)) basic_ostream;
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FWD_OSTREAM_H

libcxx/include/__fwd/sstream.h

+//===----------------------------------------------------------------------===//
+//
+// 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 _LIBCPP___FWD_SSTREAM_H
+#define _LIBCPP___FWD_SSTREAM_H
+
+#include <__config>
+#include <__fwd/string.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _CharT, class _Traits = char_traits<_CharT>,
+          class _Allocator = allocator<_CharT> >
+    class _LIBCPP_TEMPLATE_VIS basic_stringbuf;
+
+template <class _CharT, class _Traits = char_traits<_CharT>,
+          class _Allocator = allocator<_CharT> >
+    class _LIBCPP_TEMPLATE_VIS basic_istringstream;
+template <class _CharT, class _Traits = char_traits<_CharT>,
+          class _Allocator = allocator<_CharT> >
+    class _LIBCPP_TEMPLATE_VIS basic_ostringstream;
+template <class _CharT, class _Traits = char_traits<_CharT>,
+          class _Allocator = allocator<_CharT> >
+    class _LIBCPP_TEMPLATE_VIS basic_stringstream;
+
+typedef basic_stringbuf<char>        stringbuf;
+typedef basic_istringstream<char>    istringstream;
+typedef basic_ostringstream<char>    ostringstream;
+typedef basic_stringstream<char>     stringstream;
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+typedef basic_stringbuf<wchar_t>     wstringbuf;
+typedef basic_istringstream<wchar_t> wistringstream;
+typedef basic_ostringstream<wchar_t> wostringstream;
+typedef basic_stringstream<wchar_t>  wstringstream;
+#endif
+
+template <class _CharT, class _Traits, class _Allocator>
+    class _LIBCPP_PREFERRED_NAME(stringbuf) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wstringbuf)) basic_stringbuf;
+template <class _CharT, class _Traits, class _Allocator>
+    class _LIBCPP_PREFERRED_NAME(istringstream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wistringstream)) basic_istringstream;
+template <class _CharT, class _Traits, class _Allocator>
+    class _LIBCPP_PREFERRED_NAME(ostringstream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wostringstream)) basic_ostringstream;
+template <class _CharT, class _Traits, class _Allocator>
+    class _LIBCPP_PREFERRED_NAME(stringstream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wstringstream)) basic_stringstream;
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FWD_SSTREAM_H

libcxx/include/__fwd/streambuf.h

+//===----------------------------------------------------------------------===//
+//
+// 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 _LIBCPP___FWD_STREAMBUF_H
+#define _LIBCPP___FWD_STREAMBUF_H
+
+#include <__config>
+#include <__fwd/string.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _CharT, class _Traits = char_traits<_CharT> >
+    class _LIBCPP_TEMPLATE_VIS basic_streambuf;
+
+typedef basic_streambuf<char>        streambuf;
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+typedef basic_streambuf<wchar_t>     wstreambuf;
+#endif
+
+template <class _CharT, class _Traits>
+    class _LIBCPP_PREFERRED_NAME(streambuf) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wstreambuf)) basic_streambuf;
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FWD_STREAMBUF_H

libcxx/include/fstream

 }  // std
 
 */
 
 #include <__algorithm/max.h>
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__availability>
 #include <__config>
+#include <__fwd/fstream.h>
 #include <__locale>
 #include <__utility/move.h>
 #include <__utility/swap.h>
 #include <__utility/unreachable.h>
 #include <cstdio>
 #include <istream>
 #include <ostream>
 #include <typeinfo>

libcxx/include/ios

 
 #include <__config>
 
 #if defined(_LIBCPP_HAS_NO_LOCALIZATION)
 #   error "The iostreams library is not supported since libc++ has been configured without support for localization."
 #endif
 
 #include <__assert> // all public C++ headers provide the assertion handler
+#include <__fwd/ios.h>
 #include <__ios/fpos.h>
 #include <__locale>
 #include <__system_error/error_category.h>
 #include <__system_error/error_code.h>
 #include <__system_error/error_condition.h>
 #include <__system_error/system_error.h>
 #include <__utility/swap.h>
 #include <__verbose_abort>

libcxx/include/iosfwd

 using u32streampos = fpos<char_traits<char32_t>::state_type>;
 
 }  // std
 
 */
 
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
+#include <__fwd/fstream.h>
+#include <__fwd/ios.h>
+#include <__fwd/istream.h>
+#include <__fwd/ostream.h>
+#include <__fwd/sstream.h>
+#include <__fwd/streambuf.h>
 #include <__fwd/string.h>
 #include <__mbstate_t.h>
 #include <version>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 class _LIBCPP_TYPE_VIS ios_base;
 
 template <class _CharT, class _Traits = char_traits<_CharT> >
-    class _LIBCPP_TEMPLATE_VIS basic_ios;
-
-template <class _CharT, class _Traits = char_traits<_CharT> >
-    class _LIBCPP_TEMPLATE_VIS basic_streambuf;
-template <class _CharT, class _Traits = char_traits<_CharT> >
-    class _LIBCPP_TEMPLATE_VIS basic_istream;
-template <class _CharT, class _Traits = char_traits<_CharT> >
-    class _LIBCPP_TEMPLATE_VIS basic_ostream;
-template <class _CharT, class _Traits = char_traits<_CharT> >
-    class _LIBCPP_TEMPLATE_VIS basic_iostream;
-
-template <class _CharT, class _Traits = char_traits<_CharT>,
-          class _Allocator = allocator<_CharT> >
-    class _LIBCPP_TEMPLATE_VIS basic_stringbuf;
-template <class _CharT, class _Traits = char_traits<_CharT>,
-          class _Allocator = allocator<_CharT> >
-    class _LIBCPP_TEMPLATE_VIS basic_istringstream;
-template <class _CharT, class _Traits = char_traits<_CharT>,
-          class _Allocator = allocator<_CharT> >
-    class _LIBCPP_TEMPLATE_VIS basic_ostringstream;
-template <class _CharT, class _Traits = char_traits<_CharT>,
-          class _Allocator = allocator<_CharT> >
-    class _LIBCPP_TEMPLATE_VIS basic_stringstream;
-
-template <class _CharT, class _Traits = char_traits<_CharT> >
-    class _LIBCPP_TEMPLATE_VIS basic_filebuf;
-template <class _CharT, class _Traits = char_traits<_CharT> >
-    class _LIBCPP_TEMPLATE_VIS basic_ifstream;
-template <class _CharT, class _Traits = char_traits<_CharT> >
-    class _LIBCPP_TEMPLATE_VIS basic_ofstream;
-template <class _CharT, class _Traits = char_traits<_CharT> >
-    class _LIBCPP_TEMPLATE_VIS basic_fstream;
-
-template <class _CharT, class _Traits = char_traits<_CharT> >
     class _LIBCPP_TEMPLATE_VIS istreambuf_iterator;
 template <class _CharT, class _Traits = char_traits<_CharT> >
     class _LIBCPP_TEMPLATE_VIS ostreambuf_iterator;
 
-typedef basic_ios<char>              ios;
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-typedef basic_ios<wchar_t>           wios;
-#endif
-
-typedef basic_streambuf<char>        streambuf;
-typedef basic_istream<char>          istream;
-typedef basic_ostream<char>          ostream;
-typedef basic_iostream<char>         iostream;
-
-typedef basic_stringbuf<char>        stringbuf;
-typedef basic_istringstream<char>    istringstream;
-typedef basic_ostringstream<char>    ostringstream;
-typedef basic_stringstream<char>     stringstream;
-
-typedef basic_filebuf<char>          filebuf;
-typedef basic_ifstream<char>         ifstream;
-typedef basic_ofstream<char>         ofstream;
-typedef basic_fstream<char>          fstream;
-
-#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-typedef basic_streambuf<wchar_t>     wstreambuf;
-typedef basic_istream<wchar_t>       wistream;
-typedef basic_ostream<wchar_t>       wostream;
-typedef basic_iostream<wchar_t>      wiostream;
-
-typedef basic_stringbuf<wchar_t>     wstringbuf;
-typedef basic_istringstream<wchar_t> wistringstream;
-typedef basic_ostringstream<wchar_t> wostringstream;
-typedef basic_stringstream<wchar_t>  wstringstream;
-
-typedef basic_filebuf<wchar_t>       wfilebuf;
-typedef basic_ifstream<wchar_t>      wifstream;
-typedef basic_ofstream<wchar_t>      wofstream;
-typedef basic_fstream<wchar_t>       wfstream;
-#endif
-
-template <class _CharT, class _Traits>
-    class _LIBCPP_PREFERRED_NAME(ios) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wios)) basic_ios;
-
-template <class _CharT, class _Traits>
-    class _LIBCPP_PREFERRED_NAME(streambuf) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wstreambuf)) basic_streambuf;
-template <class _CharT, class _Traits>
-    class _LIBCPP_PREFERRED_NAME(istream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wistream)) basic_istream;
-template <class _CharT, class _Traits>
-    class _LIBCPP_PREFERRED_NAME(ostream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wostream)) basic_ostream;
-template <class _CharT, class _Traits>
-    class _LIBCPP_PREFERRED_NAME(iostream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wiostream)) basic_iostream;
-
-template <class _CharT, class _Traits, class _Allocator>
-    class _LIBCPP_PREFERRED_NAME(stringbuf) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wstringbuf)) basic_stringbuf;
-template <class _CharT, class _Traits, class _Allocator>
-    class _LIBCPP_PREFERRED_NAME(istringstream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wistringstream)) basic_istringstream;
-template <class _CharT, class _Traits, class _Allocator>
-    class _LIBCPP_PREFERRED_NAME(ostringstream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wostringstream)) basic_ostringstream;
-template <class _CharT, class _Traits, class _Allocator>
-    class _LIBCPP_PREFERRED_NAME(stringstream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wstringstream)) basic_stringstream;
-
-template <class _CharT, class _Traits>
-    class _LIBCPP_PREFERRED_NAME(filebuf) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wfilebuf)) basic_filebuf;
-template <class _CharT, class _Traits>
-    class _LIBCPP_PREFERRED_NAME(ifstream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wifstream)) basic_ifstream;
-template <class _CharT, class _Traits>
-    class _LIBCPP_PREFERRED_NAME(ofstream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wofstream)) basic_ofstream;
-template <class _CharT, class _Traits>
-    class _LIBCPP_PREFERRED_NAME(fstream) _LIBCPP_IF_WIDE_CHARACTERS(_LIBCPP_PREFERRED_NAME(wfstream)) basic_fstream;
-
 template <class _State>             class _LIBCPP_TEMPLATE_VIS fpos;
 typedef fpos<mbstate_t>    streampos;
 typedef fpos<mbstate_t>    wstreampos;
 #ifndef _LIBCPP_HAS_NO_CHAR8_T
 typedef fpos<mbstate_t>    u8streampos;
 #endif
 typedef fpos<mbstate_t>    u16streampos;
 typedef fpos<mbstate_t>    u32streampos;
 
-#if defined(_NEWLIB_VERSION)
-// On newlib, off_t is 'long int'
-typedef long int streamoff;         // for char_traits in <string>
-#else
-typedef long long streamoff;        // for char_traits in <string>
-#endif
-
 // Include other forward declarations here
 template <class _Tp, class _Alloc = allocator<_Tp> >
 class _LIBCPP_TEMPLATE_VIS vector;
 
 template <class _CharT, class _Traits>
 class __save_flags
 {
     typedef basic_ios<_CharT, _Traits> __stream_type;

libcxx/include/istream

template <class Stream, class T>
   Stream&& operator>>(Stream&& is, T&& x);
 
 }  // std
 
 */
 
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
+#include <__fwd/istream.h>
 #include <__iterator/istreambuf_iterator.h>
 #include <__type_traits/conjunction.h>
 #include <__type_traits/enable_if.h>
 #include <__type_traits/is_base_of.h>
 #include <__utility/declval.h>
 #include <__utility/forward.h>
 #include <ostream>
 #include <version>

libcxx/include/module.modulemap.in

module forward_list {
     export initializer_list
     export *
   }
   module fstream {
     @requires_LIBCXX_ENABLE_LOCALIZATION@
     @requires_LIBCXX_ENABLE_FSTREAM@
     header "fstream"
     export *
+    module fstream_fwd { private header "__fwd/fstream.h" }
   }
   module functional {
     header "functional"
     export *
 
     module __functional {
       module binary_function            { private header "__functional/binary_function.h" }
       module binary_negate              { private header "__functional/binary_negate.h" }
module std [system] {
   }
   module ios {
     @requires_LIBCXX_ENABLE_LOCALIZATION@
     header "ios"
     export iosfwd
     export *
 
     module __ios {
-      module fpos { private header "__ios/fpos.h" }
+      module fpos    { private header "__ios/fpos.h" }
+      module ios_fwd { private header "__fwd/ios.h" }
     }
   }
   module iosfwd {
     header "iosfwd"
     export *
   }
   module iostream {
     @requires_LIBCXX_ENABLE_LOCALIZATION@
     header "iostream"
     export ios
     export streambuf
     export istream
     export ostream
     export *
   }
   module istream {
     @requires_LIBCXX_ENABLE_LOCALIZATION@
     header "istream"
     // FIXME: should re-export ios, streambuf?
     export *
+    module istream_fwd { private header "__fwd/istream.h" }
   }
   module iterator {
     header "iterator"
     export *
 
     module __iterator {
       module access                { private header "__iterator/access.h" }
       module advance               { private header "__iterator/advance.h" }
module optional {
     header "optional"
     export *
   }
   module ostream {
     @requires_LIBCXX_ENABLE_LOCALIZATION@
     header "ostream"
     // FIXME: should re-export ios, streambuf?
     export *
+    module ostream_fwd { private header "__fwd/ostream.h" }
   }
   module queue {
     header "queue"
     export initializer_list
     export *
   }
   module random {
     header "random"
module span {
     export version
     module span_fwd { private header "__fwd/span.h" }
   }
   module sstream {
     @requires_LIBCXX_ENABLE_LOCALIZATION@
     header "sstream"
     // FIXME: should re-export istream, ostream, ios, streambuf, string?
     export *
+    module sstream_fwd { private header "__fwd/sstream.h" }
   }
   module stack {
     header "stack"
     export initializer_list
     export *
   }
   module stdexcept {
     header "stdexcept"
     export *
   }
   module streambuf {
     @requires_LIBCXX_ENABLE_LOCALIZATION@
     header "streambuf"
     export *
+    module streambuf_fwd { private header "__fwd/streambuf.h" }
   }
   module string {
     header "string"
     export initializer_list
     export string_view
     module __string {
       module char_traits           { private header "__string/char_traits.h" }
       module constexpr_c_functions { private header "__string/constexpr_c_functions.h" }

libcxx/include/ostream

 
 }  // std
 
 */
 
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
 #include <__exception/operations.h>
+#include <__fwd/ostream.h>
 #include <__memory/shared_ptr.h>
 #include <__memory/unique_ptr.h>
 #include <__system_error/error_code.h>
 #include <__type_traits/conjunction.h>
 #include <__type_traits/enable_if.h>
 #include <__type_traits/is_base_of.h>
 #include <__type_traits/void_t.h>
 #include <__utility/declval.h>

libcxx/include/sstream

 typedef basic_stringstream<wchar_t> wstringstream;
 
 }  // std
 
 */
 
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
+#include <__fwd/sstream.h>
 #include <__utility/swap.h>
 #include <istream>
 #include <ostream>
 #include <string>
 #include <version>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header

libcxx/include/streambuf

 };
 
 }  // std
 
 */
 
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
+#include <__fwd/streambuf.h>
 #include <cstdint>
 #include <ios>
 #include <iosfwd>
 #include <version>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif

libcxx/test/libcxx/private_headers.verify.cpp

 #include <__functional/pointer_to_unary_function.h> // expected-error@*:* {{use of private header from outside its module: '__functional/pointer_to_unary_function.h'}}
 #include <__functional/ranges_operations.h> // expected-error@*:* {{use of private header from outside its module: '__functional/ranges_operations.h'}}
 #include <__functional/reference_wrapper.h> // expected-error@*:* {{use of private header from outside its module: '__functional/reference_wrapper.h'}}
 #include <__functional/unary_function.h> // expected-error@*:* {{use of private header from outside its module: '__functional/unary_function.h'}}
 #include <__functional/unary_negate.h> // expected-error@*:* {{use of private header from outside its module: '__functional/unary_negate.h'}}
 #include <__functional/unwrap_ref.h> // expected-error@*:* {{use of private header from outside its module: '__functional/unwrap_ref.h'}}
 #include <__functional/weak_result_type.h> // expected-error@*:* {{use of private header from outside its module: '__functional/weak_result_type.h'}}
 #include <__fwd/array.h> // expected-error@*:* {{use of private header from outside its module: '__fwd/array.h'}}
+#include <__fwd/fstream.h> // expected-error@*:* {{use of private header from outside its module: '__fwd/fstream.h'}}
 #include <__fwd/get.h> // expected-error@*:* {{use of private header from outside its module: '__fwd/get.h'}}
 #include <__fwd/hash.h> // expected-error@*:* {{use of private header from outside its module: '__fwd/hash.h'}}
+#include <__fwd/ios.h> // expected-error@*:* {{use of private header from outside its module: '__fwd/ios.h'}}
+#include <__fwd/istream.h> // expected-error@*:* {{use of private header from outside its module: '__fwd/istream.h'}}
 #include <__fwd/memory_resource.h> // expected-error@*:* {{use of private header from outside its module: '__fwd/memory_resource.h'}}
+#include <__fwd/ostream.h> // expected-error@*:* {{use of private header from outside its module: '__fwd/ostream.h'}}
 #include <__fwd/pair.h> // expected-error@*:* {{use of private header from outside its module: '__fwd/pair.h'}}
 #include <__fwd/span.h> // expected-error@*:* {{use of private header from outside its module: '__fwd/span.h'}}
+#include <__fwd/sstream.h> // expected-error@*:* {{use of private header from outside its module: '__fwd/sstream.h'}}
+#include <__fwd/streambuf.h> // expected-error@*:* {{use of private header from outside its module: '__fwd/streambuf.h'}}
 #include <__fwd/string.h> // expected-error@*:* {{use of private header from outside its module: '__fwd/string.h'}}
 #include <__fwd/string_view.h> // expected-error@*:* {{use of private header from outside its module: '__fwd/string_view.h'}}
 #include <__fwd/subrange.h> // expected-error@*:* {{use of private header from outside its module: '__fwd/subrange.h'}}
 #include <__fwd/tuple.h> // expected-error@*:* {{use of private header from outside its module: '__fwd/tuple.h'}}
 #include <__ios/fpos.h> // expected-error@*:* {{use of private header from outside its module: '__ios/fpos.h'}}
 #include <__iterator/access.h> // expected-error@*:* {{use of private header from outside its module: '__iterator/access.h'}}
 #include <__iterator/advance.h> // expected-error@*:* {{use of private header from outside its module: '__iterator/advance.h'}}
 #include <__iterator/back_insert_iterator.h> // expected-error@*:* {{use of private header from outside its module: '__iterator/back_insert_iterator.h'}}

libcxx/utils/data/ignore_format.txt

 libcxx/include/__functional/pointer_to_unary_function.h
 libcxx/include/__functional/ranges_operations.h
 libcxx/include/__functional/reference_wrapper.h
 libcxx/include/__functional/unary_function.h
 libcxx/include/__functional/unary_negate.h
 libcxx/include/__functional/unwrap_ref.h
 libcxx/include/__functional/weak_result_type.h
 libcxx/include/future
+libcxx/include/__fwd/fstream.h
 libcxx/include/__fwd/get.h
+libcxx/include/__fwd/ios.h
+libcxx/include/__fwd/istream.h
+libcxx/include/__fwd/ostream.h
 libcxx/include/__fwd/span.h
+libcxx/include/__fwd/sstream.h
+libcxx/include/__fwd/streambuf.h
 libcxx/include/__fwd/string_view.h
 libcxx/include/__fwd/subrange.h
 libcxx/include/__hash_table
 libcxx/include/initializer_list
 libcxx/include/inttypes.h
 libcxx/include/iomanip
 libcxx/include/ios
 libcxx/include/__ios/fpos.h