Re: [PATCH] merge: use editor by default in interactive sessions

[Junio C Hamano <gitster@pobox.com>]

Junio C Hamano <gitster@pobox.com> writes:

> Erik Faye-Lund <kusmabite@gmail.com> writes:
>
>>> +       /* Use editor if stdin and stdout are the same and is a tty */
>>> +       return (!fstat(0, &st_stdin) &&
>>> +               !fstat(1, &st_stdout) &&
>>> +               isatty(0) &&
>>> +               st_stdin.st_dev == st_stdout.st_dev &&
>>> +               st_stdin.st_ino == st_stdout.st_ino &&
>>> +               st_stdin.st_mode == st_stdout.st_mode);
>>
>> I just stumbled over this code, and I got a bit worried; the
>> stat-implementation we use on Windows sets st_ino to 0, so
>> "st_stdin.st_ino == st_stdout.st_ino" will always evaluate to true.
>>
>> Perhaps we should add a check for isatty(1) here as well? ...
>> Or is there something I'm missing here?
>
> No, the intention was ...

s/No,/No, you are not missing anything./;

I'll queue it with this explanation:

    merge: do not trust fstat(2) too much when checking interactiveness
    
    The heuristic used by "git merge" to decide if it automatically gives an
    editor upon clean automerge is to see if the standard input and the
    standard output is the same device and is a tty, we are in an interactive
    session.  "The same device" test was done by comparing fstat(2) result on
    the two file descriptors (and they must match), and we asked isatty() only
    for the standard input (we insist that they are the same device and there
    is no point asking tty-ness of the standard output).
    
    The stat(2) emulation on Windows port however does not give a usable value
    in st_ino field, so even if the standard output is connected to something
    different from the standard input, "The same device" test may incorrectly
    return true. To accomodate it, add another isatty() check for the standard
    output stream as well.
    
    Reported-by: Erik Faye-Lund <kusmabite@gmail.com>
    Signed-off-by: Junio C Hamano <gitster@pobox.com>

Thanks.