Am 11.12.2016 um 12:16 schrieb Johannes Schindelin:
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;
I am sorry to have to report that this check does not work as expected.
I am operating Git from CMD, not mintty, BTW.
It fails with GetLastError() == 6 (invalid handle value). The reason for
this is, I think, that in reality we are not writing to the console
directly, but to a pipe, which is drained by console_thread(), which
writes to the console.
I have little clue what this winansi.c file is doing. Do you have any
pointers where I should start digging?
Wait...
Should we not use winansi_get_osfhandle() instead of _get_osfhandle()?
+ }
+ }
+
+ return res;
+}
+
void winansi_init(void)
{
int con1, con2;