Provide a module interface unit

include/fmt/core.h

@@ -270,6 +270,7 @@ FMT_GCC_PRAGMA("GCC optimize(\"Og\")")
 #endif
 
 FMT_BEGIN_NAMESPACE
+FMT_MODULE_EXPORT_BEGIN
 
 // Implementations of enable_if_t and other metafunctions for older systems.
 template <bool B, class T = void>
@@ -288,6 +289,8 @@ template <typename T> using type_identity_t = typename type_identity<T>::type;
 
 struct monostate {};
 
+FMT_MODULE_EXPORT_END
+
 // An enable_if helper to be used in template parameters which results in much
 // shorter symbols: https://godbolt.org/z/sWw4vP. Extra parentheses are needed
 // to workaround a bug in MSVC 2019 (see #1140 and #1186).

include/fmt/ostream.h

@@ -14,13 +14,9 @@
 
 FMT_BEGIN_NAMESPACE
 
-FMT_MODULE_EXPORT_BEGIN
-
 template <typename Char> class basic_printf_parse_context;
 template <typename OutputIt, typename Char> class basic_printf_context;
 
-FMT_MODULE_EXPORT_END
-
 namespace detail {
 
 template <class Char> class formatbuf : public std::basic_streambuf<Char> {

include/fmt/printf.h

@@ -195,13 +195,16 @@ FMT_DEPRECATED void printf(detail::buffer<Char>& buf,
 }
 using detail::vprintf;
 
-// Exported from ostream.h.
+FMT_MODULE_EXPORT_BEGIN
+
 template <typename Char>
 class basic_printf_parse_context : public basic_format_parse_context<Char> {
   using basic_format_parse_context<Char>::basic_format_parse_context;
 };
 template <typename OutputIt, typename Char> class basic_printf_context;
 
+FMT_MODULE_EXPORT_END
+
 /**
   \rst
   The ``printf`` argument formatter.

src/fmt.cc

@@ -0,0 +1,87 @@
+module;
+// put all implementation-provided headers into the global module fragment
+// to prevent attachment to this module
+#if !defined(_CRT_SECURE_NO_WARNINGS) && defined(_MSC_VER)
+#  define _CRT_SECURE_NO_WARNINGS
+#endif
+#if !defined(WIN32_LEAN_AND_MEAN) && defined(_WIN32)
+#  define WIN32_LEAN_AND_MEAN
+#endif
+
+#include <cctype>
+#include <cerrno>
+#include <climits>
+#include <clocale>
+#include <cmath>
+#include <cstdarg>
+#include <cstddef>
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+#include <ctime>
+#include <cwchar>
+
+#include <algorithm>
+#include <chrono>
+#include <exception>
+#include <functional>
+#include <iterator>
+#include <limits>
+#include <locale>
+#include <memory>
+#include <ostream>
+#include <sstream>
+#include <stdexcept>
+#include <string>
+#include <string_view>
+#include <type_traits>
+#include <utility>
+#include <vector>
+
+#if _MSC_VER
+#  include <intrin.h>
+#endif
+#if defined __APPLE__ || defined(__FreeBSD__)
+#  include <xlocale.h>
+#endif
+#if __has_include(<winapifamily.h>)
+#  include <winapifamily.h>
+#endif
+#if (__has_include(<fcntl.h>) || defined(__APPLE__) || \
+     defined(__linux__)) &&                            \
+    (!defined(WINAPI_FAMILY) || (WINAPI_FAMILY == WINAPI_FAMILY_DESKTOP_APP))
+#  include <fcntl.h>
+#  include <sys/stat.h>
+#  include <sys/types.h>
+#  ifndef _WIN32
+#    include <unistd.h>
+#  else
+#    include <io.h>
+#  endif
+#endif
+#ifdef _WIN32
+#  include <windows.h>
+#endif
+
+export module fmt;
+
+#define FMT_MODULE_EXPORT export
+#define FMT_MODULE_EXPORT_BEGIN export {
+#define FMT_MODULE_EXPORT_END }
+
+// all library-provided declarations and definitions
+// must be in the module purview to be exported
+#include "fmt/format.h"
+#include "fmt/args.h"
+#include "fmt/color.h"
+#include "fmt/compile.h"
+#include "fmt/locale.h"
+#include "fmt/chrono.h"
+#include "fmt/printf.h"
+#include "fmt/os.h"
+
+module : private;
+
+#include "format.cc"
+#include "os.cc"