[PATCH 0/1] Fix a long-standing isatty() problem on Windows

I finally got a chance to debug the problems with the ever-timing-out test runs of `pu` on Windows. Turns out that pb/bisect uncovered a really old, really bad bug: on Windows, isatty() does not do what Git expects, at least not completely: it detects interactive terminals *and character devices*.

Why is this such a big deal?

One such character device is NUL, Windows' equivalent of /dev/null. And guess what happens when the new tests of the bisect--helper run, with stdin redirected from /dev/null? Precisely. Git asks "the user" for reassurance that it may really continue, waiting forever. Or for Ctrl+C.

As we know what Git's source code wants, we have to make extra certain to test whether isatty() reports success for a Console. The common way to do this is to run GetConsoleMode() for input file descriptors, and GetConsoleScreenBufferInfo() for output file descriptors.

One additional note: the new winansi_isatty() function was put into this particular spot not only because it vaguely makes sense to put tty-related stuff into compat/winansi.c, but with required future changes in mind:

The current way in which Git for Windows makes sure that isatty() returns non-zero for Git Bash (which runs in a terminal emulator called MinTTY that does *not* have any Windows Console associated with it, and therefore Windows' _isatty() would actually return 0 if it was not for our detect_msys_tty() function) is hacky and needs to be fixed properly.

It is hacky because it relies on internals of the MSVC runtime that do not hold true for the new Universal runtimes, which are used when compiling with Visual C.

We already have experimental code to future-proof this method, and we use that already when compiling Git for Windows in Visual Studio.

The place in which winansi_isatty() now lives will hopefully make it possible to unify the code paths again, so that both GCC and Visual C use detect_msys_tty() through winansi_isatty().

This will also fix a bug where current Visual C-built Git may misdetect a reopened stdin to be connected to an interactive terminal.

Johannes Schindelin (1):
  mingw: intercept isatty() to handle /dev/null as Git expects it

 compat/mingw.h   |  3 +++
 compat/winansi.c | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

base-commit: 8d7a455ed52e2a96debc080dfc011b6bb00db5d2
Published-As: https://github.com/dscho/git/releases/tag/mingw-isatty-v1
Fetch-It-Via: git fetch https://github.com/dscho/git mingw-isatty-v1