[libcxx-commits] [libcxx] [libc++][modules] Adds std.compat module. (PR #71438)

[Chuanqi Xu via libcxx-commits]

================
@@ -0,0 +1,202 @@
+// -*- 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
+//
+//===----------------------------------------------------------------------===//
+
+// WARNING, this entire header is generated by
+// utils/generate_libcxx_cppm_in.py
+// DO NOT MODIFY!
+
+module;
+
+#include <__config>
+
+// 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>
+#include <cstddef>
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+#include <ctime>
+#include <cuchar>
+#if !defined(_LIBCPP_HAS_NO_WIDE_CHARACTERS)
+#  include <cwchar>
+#endif
+#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
+#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(<flat_map>)
+#  error "update the header information for <flat_map> in headers_not_available in utils/libcxx/header_information.py"
+#endif // __has_include(<flat_map>)
+#if __has_include(<flat_set>)
+#  error "update the header information for <flat_set> in headers_not_available in utils/libcxx/header_information.py"
+#endif // __has_include(<flat_set>)
+#if __has_include(<generator>)
+#  error "update the header information for <generator> in headers_not_available in utils/libcxx/header_information.py"
+#endif // __has_include(<generator>)
+#if __has_include(<hazard_pointer>)
+#  error "update the header information for <hazard_pointer> in headers_not_available in utils/libcxx/header_information.py"
+#endif // __has_include(<hazard_pointer>)
+#if __has_include(<rcu>)
+#  error "update the header information for <rcu> in headers_not_available in utils/libcxx/header_information.py"
+#endif // __has_include(<rcu>)
+#if __has_include(<spanstream>)
+#  error "update the header information for <spanstream> in headers_not_available in utils/libcxx/header_information.py"
+#endif // __has_include(<spanstream>)
+#if __has_include(<stacktrace>)
+#  error "update the header information for <stacktrace> in headers_not_available in utils/libcxx/header_information.py"
+#endif // __has_include(<stacktrace>)
+#if __has_include(<stdfloat>)
+#  error "update the header information for <stdfloat> in headers_not_available in utils/libcxx/header_information.py"
+#endif // __has_include(<stdfloat>)
+#if __has_include(<syncstream>)
+#  error "update the header information for <syncstream> in headers_not_available in utils/libcxx/header_information.py"
+#endif // __has_include(<syncstream>)
+#if __has_include(<text_encoding>)
+#  error "update the header information for <text_encoding> in headers_not_available in utils/libcxx/header_information.py"
+#endif // __has_include(<text_encoding>)
+
+export module std.compat;
+
+ at LIBCXX_MODULE_STD_INCLUDE_SOURCES@
+ at LIBCXX_MODULE_STD_COMPAT_INCLUDE_SOURCES@
----------------
ChuanqiXu9 wrote:

```suggestion
export module std.compat;
export import std;

@LIBCXX_MODULE_STD_COMPAT_INCLUDE_SOURCES@
```

I feel this may have better compile-time performance when users write:

```
import std;
import std.compat;
```

In this case, the compiler needs to handle the redeclarations in module std and module std.compat. Then it may have the same problem as we discussed before.

While the example itself looks ridiculous, I feel it is highly possible in real worlds:

```
// a.cppm
export module a;
import std;

// b.cppm
export module b;
import std.compat;

// some_user.cc
import a;
import b;
```

Then the compiler needs to handle the redeclarations.

https://github.com/llvm/llvm-project/pull/71438