mintty on windows always uses pipes to connect stdout between processes
and for the terminal output. The previous implementation always assumed
that stdout connected to a pipe means that stdout is displayed on a
mintty terminal. However, this detection breaks when using pipes to
connect processes and for powershell which uses pipes when redirecting
to a file.
Now the pipe filename is queried and matched against the pattern used by
msys / cygwin when connected to the terminal. In all other cases assume
that a pipe is just a regular pipe.
Previously the progress bar / status update interval used
stdoutIsTerminal to determine whether it is possible to update the
progress bar or not. However, its implementation differed from the
detection within the backup command which included additional checks to
detect the presence of mintty on Windows. mintty behaves like a terminal
but uses pipes for communication.
This adds stdoutCanUpdateStatus() which calls the same terminal detection
code used by backup. This ensures that all commands consistently switch
between interactive and non-interactive terminal mode.
stdoutIsTerminal() now also returns true whenever stdoutCanUpdateStatus()
does so. This is required to properly handle the special case of mintty.
The canUpdateStatus check was simplified in #2608, but it accidentally flipped
the condition. The correct check is as follows: If the output is a pipe then
restic probably runs in mintty/cygwin. In that case it's possible to
update the output status. In all other cases it isn't.
This commit inverts to condition again to offer the previous and correct
behavior.
This now keeps the cursor at the first column of the first status line
so that messages printed to stdout or stderr by some other part of the
progarm will still be visible. The message will overwrite the status
lines, but those are easily reprinted on the next status update.
