When Git's source code calls isatty(), it really asks whether the respective file descriptor is connected to an interactive terminal. Windows' _isatty() function, however, determines whether the file descriptor is associated with a character device. And NUL, Windows' equivalent of /dev/null, is a character device. Which means that for years, Git mistakenly detected an associated interactive terminal when being run through the test suite, which almost always redirects stdin, stdout and stderr to /dev/null. This bug only became obvious, and painfully so, when the new bisect--helper entered the `pu` branch and made the automatic build & test time out because t6030 was waiting for an answer. For details, see https://msdn.microsoft.com/en-us/library/f4s0ddew.aspx Signed-off-by: Johannes Schindelin <johannes.schindelin@xxxxxx> --- compat/mingw.h | 3 +++ compat/winansi.c | 33 +++++++++++++++++++++++++++++++++ 2 files changed, 36 insertions(+) diff --git a/compat/mingw.h b/compat/mingw.h index 034fff9479..3350169555 100644 --- a/compat/mingw.h +++ b/compat/mingw.h @@ -384,6 +384,9 @@ int mingw_raise(int sig); * ANSI emulation wrappers */ +int winansi_isatty(int fd); +#define isatty winansi_isatty + void winansi_init(void); HANDLE winansi_get_osfhandle(int fd); diff --git a/compat/winansi.c b/compat/winansi.c index db4a5b0a37..cb725fb02f 100644 --- a/compat/winansi.c +++ b/compat/winansi.c @@ -7,6 +7,9 @@ #include <wingdi.h> #include <winreg.h> +/* In this file, we actually want to use Windows' own isatty(). */ +#undef isatty + /* ANSI codes used by git: m, K @@ -570,6 +573,36 @@ static void detect_msys_tty(int fd) #endif +int winansi_isatty(int fd) +{ + int res = isatty(fd); + + if (res) { + /* + * Make sure that /dev/null is not fooling Git into believing + * that we are connected to a terminal, as "_isatty() returns a + * nonzero value if the descriptor is associated with a + * character device."; for more information, see + * + * https://msdn.microsoft.com/en-us/library/f4s0ddew.aspx + */ + HANDLE handle = (HANDLE)_get_osfhandle(fd); + if (fd == STDIN_FILENO) { + DWORD dummy; + + if (!GetConsoleMode(handle, &dummy)) + res = 0; + } else if (fd == STDOUT_FILENO || fd == STDERR_FILENO) { + CONSOLE_SCREEN_BUFFER_INFO dummy; + + if (!GetConsoleScreenBufferInfo(handle, &dummy)) + res = 0; + } + } + + return res; +} + void winansi_init(void) { int con1, con2; -- 2.11.0.rc3.windows.1