[libc++] Adjust how we guard the inclusion of unistd.h

[john.brawn]

Summary

unistd.h isn't guaranteed to exist when the target isn't Windows, in particular if the target is bare-metal (i.e. no operating system). Handle this by using __has_include instead, though in filesystem/operations.cpp we already unconditionally include it so just remove the extra include.

[ldionne]

libcxx/include/__config

1556

Naive question: why not use __has_include?

libcxx/src/filesystem/operations.cpp

40

You're not including it anymore?

[LittleFox94]

libcxx/src/filesystem/operations.cpp

40

It's done unconditionally in line 22

[ldionne]

libcxx/src/filesystem/operations.cpp

40

Good catch!

[john.brawn]

libcxx/include/__config

1556

Because I didn't know about it. Looks like all the compiler version we support (in llvm/cmake/modules/CheckCompilerVersion.cmake) implement it, so it makes sense to use it.

libcxx/include/__config

 
 // Support for _FILE_OFFSET_BITS=64 landed gradually in Android, so the full set
 // of functions used in cstdio may not be available for low API levels when
 // using 64-bit file offsets on LP32.
 #if defined(__BIONIC__) && defined(__USE_FILE_OFFSET64) && __ANDROID_API__ < 24
 #define _LIBCPP_HAS_NO_FGETPOS_FSETPOS
 #endif
 
+#if defined(__unix__) || (defined(__APPLE__) && defined(__MACH__)) || defined(__CloudABI__) || defined(__Fuchsia__) || defined(__wasi__)
+#define _LIBCPP_HAS_UNISTD
+#endif
+
 #endif // __cplusplus
 
 #endif // _LIBCPP_CONFIG

libcxx/src/chrono.cpp

 //===------------------------- chrono.cpp ---------------------------------===//
 //
 // 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 "chrono"
 #include "cerrno"        // errno
 #include "system_error"  // __throw_system_error
 #include <time.h>        // clock_gettime, CLOCK_MONOTONIC and CLOCK_REALTIME
 #include "include/apple_availability.h"
 
-#if !defined(_WIN32)
+#if defined(_LIBCPP_HAS_UNISTD)
 #include <unistd.h>
 #endif
 
 #if !defined(__APPLE__) && _POSIX_TIMERS > 0
 #define _LIBCPP_USE_CLOCK_GETTIME
 #endif
 
 #if defined(_LIBCPP_WIN32API)

libcxx/src/filesystem/operations.cpp

 #include <sys/sendfile.h>
 #define _LIBCPP_USE_SENDFILE
 #endif
 #elif defined(__APPLE__) || __has_include(<copyfile.h>)
 #include <copyfile.h>
 #define _LIBCPP_USE_COPYFILE
 #endif
 
-#if !defined(_WIN32)
-#include <unistd.h>
-#endif
-
 #if !defined(__APPLE__) && _POSIX_TIMERS > 0
 #define _LIBCPP_USE_CLOCK_GETTIME
 #endif
 
 #if !defined(CLOCK_REALTIME) || !defined(_LIBCPP_USE_CLOCK_GETTIME)
 #include <sys/time.h> // for gettimeofday and timeval
 #endif                // !defined(CLOCK_REALTIME)
 

libcxx/src/thread.cpp

 
 #if defined(__unix__) || (defined(__APPLE__) && defined(__MACH__))
 # include <sys/param.h>
 # if defined(__FreeBSD__) || defined(__NetBSD__) || defined(__OpenBSD__) || defined(__DragonFly__) || defined(__APPLE__)
 #   include <sys/sysctl.h>
 # endif
 #endif // defined(__unix__) || (defined(__APPLE__) && defined(__MACH__))
 
-#if defined(__unix__) || (defined(__APPLE__) && defined(__MACH__)) || defined(__CloudABI__) || defined(__Fuchsia__) || defined(__wasi__)
-# include <unistd.h>
-#endif // defined(__unix__) || (defined(__APPLE__) && defined(__MACH__)) || defined(__CloudABI__) || defined(__Fuchsia__) || defined(__wasi__)
+#if defined(_LIBCPP_HAS_UNISTD)
+#include <unistd.h>
+#endif
 
 #if defined(__NetBSD__)
 #pragma weak pthread_create // Do not create libpthread dependency
 #endif
 
 #if defined(_LIBCPP_WIN32API)
 #include <windows.h>
 #endif