tree c78c409f1fde1425843d2b53bfc58d14be589274
parent c5eadcaab1d3969a4fbc009c65be622271edddd9
author Jeff King <peff@peff.net> 1427082845 -0400
committer Junio C Hamano <gitster@pobox.com> 1427085562 -0700

run-command: forbid using run_command with piped output

Because run_command both spawns and wait()s for the command
before returning control to the caller, any reads from the
pipes we open must necessarily happen after wait() returns.
This can lead to deadlock, as the child process may block
on writing to us while we are blocked waiting for it to
exit.

Worse, it only happens when the child fills the pipe
buffer, which means that the problem may come and go
depending on the platform and the size of the output
produced by the child.

Let's detect and flag this dangerous construct so that we
can catch potential bugs early in the test suite rather than
having them happen in the field.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>