Fix git-am safety checks

An earlier commit cbd64af added a check that prevents "git-am"
to run without its standard input connected to a terminal while
resuming operation.  This was to catch a user error to try
feeding a new patch from its standard input while recovery.

The assumption of the check was that it is an indication that a
new patch is being fed if the standard input is not connected to
a terminal.  It is however not quite correct (the standard input
can be /dev/null if the user knows the operation does not need
any input, for example).  This broke t3403 when the test was run
with its standard input connected to /dev/null.

When git-am is given an explicit command such as --skip, there
is no reason to insist that the standard input is a terminal; we
are not going to read a new patch anyway.

Credit goes to Gerrit Pape for noticing and reporting the
problem with t3403-rebase-skip test.

Signed-off-by: Junio C Hamano <junkio@cox.net>

diff --git a/git-am.sh b/git-am.sh
index d0af786aec3f797943290cdc63fa77f393900160..afe322b20fb0b40dfeb1cb17dc3cad09096e943a 100755 (executable)
--- a/git-am.sh
+++ b/git-am.sh
@@ -166,10 +166,25 @@ fi
 
 if test -d "$dotest"
 then
-       if test ",$#," != ",0," || ! tty -s
-       then
-               die "previous dotest directory $dotest still exists but mbox given."
-       fi
+       case "$#,$skip$resolved" in
+       0,*t*)
+               # Explicit resume command and we do not have file, so
+               # we are happy.
+               : ;;
+       0,)
+               # No file input but without resume parameters; catch
+               # user error to feed us a patch from standard input
+               # when there is already .dotest.  This is somewhat
+               # unreliable -- stdin could be /dev/null for example
+               # and the caller did not intend to feed us a patch but
+               # wanted to continue unattended.
+               tty -s
+               ;;
+       *)
+               false
+               ;;
+       esac ||
+       die "previous dotest directory $dotest still exists but mbox given."
        resume=yes
 else
        # Make sure we are not given --skip nor --resolved