Re: Is t7006-pager.sh racy?

On Sun, Oct 24, 2021 at 07:03:49PM +0200, SZEDER Gábor wrote:

quoted

What makes us expect that the "git log" invocation should trigger a
SIGPIPE in the first place?

A misunderstanding, perhaps, because those 'git log' commands with
their early-exiting pagers rarely trigger SIGPIPE.

I happened to be looking in this area today[1], and I think it turns out
not to be "rarely", but rather "never" for some of the tests.

The test in question sets the pager to "does-not-exist". But in that
case we will realize immediately via run-command.c that we could not run
the pager, and will not even redirect our stdout to it.

For example, doing this:

  GIT_PAGER=does-not-exist git -c alias.foo='!yes' -p foo

will never get SIGPIPE; it will just write infinitely to the original
stdout, and return success.

Whereas this:

  GIT_PAGER=false git -c alias.foo='!yes' -p foo

will reliably get SIGPIPE. But even if we used it (with a while loop to
instead of "yes" address the portability concern), the tests in t7006
would still be wrong, because they are sending test-terminal's output to
a closed pipe (so we'd still see SIGPIPE regardless of Git's behavior).
They should be sending test_terminal's output to a file or /dev/null.

It seems like this thread stalled. Ævar, were you planning to fix these
tests?

It's not too hard to swap out a "yes" as I showed above, but it further
confuses the trace2 output, because now we have the child yes (or its
shell equivalent) exiting as well.

The non-child "log --stdin" example I gave earlier in the thread avoids
that, but the fifo hackery is so horrible that I'd just as soon avoid
it. I guess yet another option is a builtin which produces infinite
output. Perhaps:

  oid=$(git rev-parse HEAD)
  while true; do echo $oid; done |
  test_terminal git -p cat-file --batch-check

That's guaranteed to get SIGPIPE eventually if the pager stops reading.
I seem to recall that test_terminal's handling of stdin is somewhat
broken, though, and would probably get in our way[2]. Possibly we could
just rip it out, as nobody is relying on it (they can't be, because it's
broken).

-Peff

[1] https://lore.kernel.org/git/YZqSBlvzz2KgOMnJ@coredump.intra.peff.net/ (local)

[2] https://lore.kernel.org/git/20190520125016.GA13474@sigill.intra.peff.net/ (local)