// mcpp.platform.terminal — terminal capability detection.

//

// Provides:

// is_tty() — whether stdout is a terminal

// terminal_cols() — terminal width in columns

module;

#include <cstdio>

#include <cstdlib>

#ifdef __unix__

#include <unistd.h>

#include <sys/ioctl.h>

#endif

#if defined(_WIN32)

#include <io.h> // _dup, _dup2, _close, _get_osfhandle

#ifndef WIN32_LEAN_AND_MEAN

#define WIN32_LEAN_AND_MEAN

#endif

#ifndef NOMINMAX

#define NOMINMAX

#endif

#include <windows.h> // SetHandleInformation, HANDLE_FLAG_INHERIT

#else

#include <unistd.h> // dup2, close

#include <fcntl.h> // fcntl, F_DUPFD_CLOEXEC

#endif

export module mcpp.platform.terminal;

import std;

export namespace mcpp::platform::terminal {

// Returns true if stdout is connected to a terminal (TTY).

bool is_tty();

// Returns the terminal width in columns. Tries TIOCGWINSZ on Unix,

// falls back to $COLUMNS, then defaults to 80.

std::size_t cols();

// EVERYTHING WRITTEN TO STANDARD OUTPUT GOES TO STANDARD ERROR UNTIL THIS IS

// DESTROYED.

//

// The redirection is made at the file descriptor, so a child process that

// inherits standard output follows it, and so does narration that prints to

// stdout without consulting any quiet flag. A command whose standard output is

// a document (`mcpp emit build-database`) plans under one of these and prints

// the document after it is gone: people still see the progress, on stderr, and

// the document arrives alone.

//

// THE SAVED DESCRIPTOR IS NOT INHERITED. It is the caller's pipe, and a child

// started during the redirection (a build program, an xlings refresh) that

// inherited it would keep the caller from reading end-of-file for as long as

// the child lives, however long after mcpp itself exited. Measured

// (mcpp-community/mcpp#648): a build program started by

// `emit build-database` held the caller's pipe as its descriptor 3. The copy

// is therefore close-on-exec on POSIX and not inheritable on Windows, so a

// child receives only descriptors 0 to 2, and 1 is standard error here.

class StdoutToStderr {

public:

StdoutToStderr();

~StdoutToStderr();

StdoutToStderr(const StdoutToStderr&) = delete;

StdoutToStderr& operator=(const StdoutToStderr&) = delete;

private:

int saved_ = -1;

};

} // namespace mcpp::platform::terminal

namespace mcpp::platform::terminal {

bool is_tty() {

#ifdef __unix__

return ::isatty(::fileno(stdout)) != 0;

#else

return false;

#endif

}

std::size_t cols() {

#ifdef __unix__

struct winsize w{};

if (::ioctl(::fileno(stdout), TIOCGWINSZ, &w) == 0 && w.ws_col > 0)

return w.ws_col;

#endif

if (auto* e = std::getenv("COLUMNS"); e && *e) {

try { auto n = std::stoul(e); if (n > 0) return n; } catch (...) {}

}

return 80;

}

StdoutToStderr::StdoutToStderr() {

std::fflush(stdout);

#if defined(_WIN32)

saved_ = ::_dup(1);

if (saved_ >= 0) {

// `_dup` duplicates the handle as inheritable, and CreateProcess with

// handle inheritance (every `_popen` and `system`) passes it on.

const auto h = reinterpret_cast<HANDLE>(::_get_osfhandle(saved_));

if (h != INVALID_HANDLE_VALUE)

::SetHandleInformation(h, HANDLE_FLAG_INHERIT, 0);

::_dup2(2, 1);

}

#else

// Not `dup`: its copy survives exec. Descriptor 3 or above, as `dup`

// would have chosen, so nothing else about the redirection moves.

saved_ = ::fcntl(1, F_DUPFD_CLOEXEC, 3);

if (saved_ >= 0) ::dup2(2, 1);

#endif

}

StdoutToStderr::~StdoutToStderr() {

std::fflush(stdout);

if (saved_ < 0) return;

#if defined(_WIN32)

::_dup2(saved_, 1);

::_close(saved_);

#else

::dup2(saved_, 1);

::close(saved_);

#endif

}

} // namespace mcpp::platform::terminal