[libc++] Guard fileno() and isatty() usage correctly.

[wecing]

See 1 and 2. isatty() is part of unistd.h, but fileno() is in stdio.h, and is guarded by _POSIX_C_SOURCE >= 1 (on my machine, man 3 fileno only requires defined(_POSIX_C_SOURCE), though).

I ran into this issue while trying to compile libc++ for a bare metal environment with Newlib as the libc. Newlib defines fileno() in stdio.h, and its unistd.h does not include stdio.h.

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: Chenguang Wang (wecing)

Changes

See 1 and 2. isatty() is part of unistd.h, but fileno() is in stdio.h, and is guarded by _POSIX_C_SOURCE >= 1 (on my machine, man 3 fileno only requires defined(_POSIX_C_SOURCE), though).

I ran into this issue while trying to compile libc++ for a bare metal environment with Newlib as the libc. Newlib defines fileno() in stdio.h, and its unistd.h does not include stdio.h.

---

Full diff: https://github.com/llvm/llvm-project/pull/166668.diff

1 Files Affected:

• (modified) libcxx/src/print.cpp (+5-2)

diff --git a/libcxx/src/print.cpp b/libcxx/src/print.cpp
index 3f2baa6dcc60b..e7ff60ba58dac 100644
--- a/libcxx/src/print.cpp
+++ b/libcxx/src/print.cpp
@@ -20,8 +20,11 @@
 #  define NOMINMAX
 #  include <io.h>
 #  include <windows.h>
-#elif __has_include(<unistd.h>)
+#elif __has_include(<unistd.h>) && __has_include(<stdio.h>) && \
+      defined(_POSIX_C_SOURCE) && _POSIX_C_SOURCE >= 1
+#  include <stdio.h>
 #  include <unistd.h>
+#  define HAS_FILENO_AND_ISATTY
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
@@ -56,7 +59,7 @@ __write_to_windows_console([[maybe_unused]] FILE* __stream, [[maybe_unused]] wst
 }
 #  endif // _LIBCPP_HAS_WIDE_CHARACTERS
 
-#elif __has_include(<unistd.h>) // !_LIBCPP_WIN32API
+#elif defined(HAS_FILENO_AND_ISATTY) // !_LIBCPP_WIN32API
 
 _LIBCPP_EXPORTED_FROM_ABI bool __is_posix_terminal(FILE* __stream) { return isatty(fileno(__stream)); }
 #endif

[wecing]

Looks like this commit broke macos, freebsd, and android. Need to investigate how to guard properly on these platforms.

[wecing]

Updated the implementation, and tests seem to be passing now.

I added a special handling logic for Newlib only; other platforms should not be affected. The defined(_NEWLIB_VERSION) trick is used in other places within libc++ as well, e.g. here.

The _NEWLIB_VERSION symbol will be visible if you include e.g. Newlib's unistd.h. Newlib's fileno is guarded by __POSIX_VISIBLE.

[philnik777]

@wecing Reviews in libc++ aren't optional. Please wait next time. If you don't get any comments within a week feel free to ping.

[wecing]

@wecing Reviews in libc++ aren't optional. Please wait next time. If you don't get any comments within a week feel free to ping.

I see. My apologies! Thanks for letting me know.