[libc++][modules] Improves std.compat module. (#76330)

Let the std.compat module use the std module instead of duplicating the
exports.

Based on @ChuanqiXu9's suggestion in #71438.

libcxx/modules/std.compat.cppm.in

@@ -17,38 +17,17 @@ module;
 
 // The headers of Table 24: C++ library headers [tab:headers.cpp]
 // and the headers of Table 25: C++ headers for C library facilities [tab:headers.cpp.c]
-#include <algorithm>
-#include <any>
-#include <array>
-#if !defined(_LIBCPP_HAS_NO_ATOMIC_HEADER)
-#  include <atomic>
-#endif
-#if !defined(_LIBCPP_HAS_NO_THREADS)
-#  include <barrier>
-#endif
-#include <bit>
-#include <bitset>
 #include <cassert>
 #include <cctype>
 #include <cerrno>
 #include <cfenv>
 #include <cfloat>
-#include <charconv>
-#include <chrono>
 #include <cinttypes>
 #include <climits>
 #if !defined(_LIBCPP_HAS_NO_LOCALIZATION)
 #  include <clocale>
 #endif
 #include <cmath>
-#if !defined(_LIBCPP_HAS_NO_LOCALIZATION)
-#  include <codecvt>
-#endif
-#include <compare>
-#include <complex>
-#include <concepts>
-#include <condition_variable>
-#include <coroutine>
 #include <csetjmp>
 #include <csignal>
 #include <cstdarg>
@@ -65,107 +44,6 @@ module;
 #if !defined(_LIBCPP_HAS_NO_WIDE_CHARACTERS)
 #  include <cwctype>
 #endif
-#include <deque>
-#include <exception>
-#include <execution>
-#include <expected>
-#include <filesystem>
-#include <format>
-#include <forward_list>
-#if !defined(_LIBCPP_HAS_NO_LOCALIZATION)
-#  include <fstream>
-#endif
-#include <functional>
-#if !defined(_LIBCPP_HAS_NO_THREADS)
-#  include <future>
-#endif
-#include <initializer_list>
-#if !defined(_LIBCPP_HAS_NO_LOCALIZATION)
-#  include <iomanip>
-#endif
-#if !defined(_LIBCPP_HAS_NO_LOCALIZATION)
-#  include <ios>
-#endif
-#include <iosfwd>
-#if !defined(_LIBCPP_HAS_NO_LOCALIZATION)
-#  include <iostream>
-#endif
-#if !defined(_LIBCPP_HAS_NO_LOCALIZATION)
-#  include <istream>
-#endif
-#include <iterator>
-#if !defined(_LIBCPP_HAS_NO_THREADS)
-#  include <latch>
-#endif
-#include <limits>
-#include <list>
-#if !defined(_LIBCPP_HAS_NO_LOCALIZATION)
-#  include <locale>
-#endif
-#include <map>
-#include <mdspan>
-#include <memory>
-#include <memory_resource>
-#include <mutex>
-#include <new>
-#include <numbers>
-#include <numeric>
-#include <optional>
-#if !defined(_LIBCPP_HAS_NO_LOCALIZATION)
-#  include <ostream>
-#endif
-#include <print>
-#include <queue>
-#include <random>
-#include <ranges>
-#include <ratio>
-#if !defined(_LIBCPP_HAS_NO_LOCALIZATION)
-#  include <regex>
-#endif
-#include <scoped_allocator>
-#if !defined(_LIBCPP_HAS_NO_THREADS)
-#  include <semaphore>
-#endif
-#include <set>
-#if !defined(_LIBCPP_HAS_NO_THREADS)
-#  include <shared_mutex>
-#endif
-#include <source_location>
-#include <span>
-#if !defined(_LIBCPP_HAS_NO_LOCALIZATION)
-#  include <sstream>
-#endif
-#include <stack>
-#include <stdexcept>
-#if !defined(_LIBCPP_HAS_NO_THREADS)
-#  include <stop_token>
-#endif
-#if !defined(_LIBCPP_HAS_NO_LOCALIZATION)
-#  include <streambuf>
-#endif
-#include <string>
-#include <string_view>
-#if !defined(_LIBCPP_HAS_NO_LOCALIZATION)
-#  include <strstream>
-#endif
-#if !defined(_LIBCPP_HAS_NO_LOCALIZATION)
-#  include <syncstream>
-#endif
-#include <system_error>
-#if !defined(_LIBCPP_HAS_NO_THREADS)
-#  include <thread>
-#endif
-#include <tuple>
-#include <type_traits>
-#include <typeindex>
-#include <typeinfo>
-#include <unordered_map>
-#include <unordered_set>
-#include <utility>
-#include <valarray>
-#include <variant>
-#include <vector>
-#include <version>
 
 // *** Headers not yet available ***
 #if __has_include(<debugging>)
@@ -203,6 +81,7 @@ module;
 #endif // __has_include(<text_encoding>)
 
 export module std.compat;
+export import std;
+
 
-@LIBCXX_MODULE_STD_INCLUDE_SOURCES@
 @LIBCXX_MODULE_STD_COMPAT_INCLUDE_SOURCES@

libcxx/modules/std.cppm.in

@@ -204,4 +204,5 @@ module;
 
 export module std;
 
+
 @LIBCXX_MODULE_STD_INCLUDE_SOURCES@

libcxx/test/libcxx/module_std_compat.gen.py

@@ -21,6 +21,7 @@
 import sys
 
 sys.path.append(sys.argv[1])
+from libcxx.header_information import module_c_headers
 from libcxx.test.modules import module_test_generator
 
 generator = module_test_generator(
@@ -37,27 +38,5 @@ generator = module_test_generator(
 print("//--- module_std_compat.sh.cpp")
 generator.write_test(
     "std.compat",
-    [
-        "cassert",
-        "cctype",
-        "cerrno",
-        "cfenv",
-        "cfloat",
-        "cinttypes",
-        "climits",
-        "clocale",
-        "cmath",
-        "csetjmp",
-        "csignal",
-        "cstdarg",
-        "cstddef",
-        "cstdint",
-        "cstdio",
-        "cstdlib",
-        "cstring",
-        "ctime",
-        "cuchar",
-        "cwchar",
-        "cwctype",
-    ],
+    module_c_headers,
 )

libcxx/utils/generate_libcxx_cppm_in.py

@@ -9,6 +9,7 @@
 import os.path
 import sys
 
+from libcxx.header_information import module_c_headers
 from libcxx.header_information import module_headers
 from libcxx.header_information import header_restrictions
 from libcxx.header_information import headers_not_available
@@ -44,7 +45,7 @@ module;
 // and the headers of Table 25: C++ headers for C library facilities [tab:headers.cpp.c]
 """
         )
-        for header in module_headers:
+        for header in module_headers if module == "std" else module_c_headers:
             if header in header_restrictions:
                 module_cpp_in.write(
                     f"""\
@@ -69,8 +70,9 @@ module;
         module_cpp_in.write(
             f"""
 export module {module};
+{'export import std;' if module == 'std.compat' else ''}
 
-@LIBCXX_MODULE_STD_INCLUDE_SOURCES@
+{'@LIBCXX_MODULE_STD_INCLUDE_SOURCES@' if module == 'std' else ''}
 {'@LIBCXX_MODULE_STD_COMPAT_INCLUDE_SOURCES@' if module == 'std.compat' else ''}"""
         )
 

libcxx/utils/libcxx/header_information.py

@@ -215,3 +215,28 @@ module_headers = [
     # These headers have been removed in C++20 so are never part of a module.
     and not header in ["ccomplex", "ciso646", "cstdbool", "ctgmath"]
 ]
+
+# The C headers used in the std and std.compat modules.
+module_c_headers = [
+    "cassert",
+    "cctype",
+    "cerrno",
+    "cfenv",
+    "cfloat",
+    "cinttypes",
+    "climits",
+    "clocale",
+    "cmath",
+    "csetjmp",
+    "csignal",
+    "cstdarg",
+    "cstddef",
+    "cstdint",
+    "cstdio",
+    "cstdlib",
+    "cstring",
+    "ctime",
+    "cuchar",
+    "cwchar",
+    "cwctype",
+]

libcxx/utils/libcxx/test/format.py

@@ -171,6 +171,7 @@ def parseScript(test, preamble):
                 "%dbg(MODULE std.compat) %{cxx} %{flags} "
                 f"{compileFlags} "
                 "-Wno-reserved-module-identifier -Wno-reserved-user-defined-literal "
+                "-fmodule-file=std=%T/std.pcm " # The std.compat module imports std.
                 "--precompile -o %T/std.compat.pcm -c %{module}/std.compat.cppm",
             )
             moduleCompileFlags.extend(