git-grep has always disallowed grepping in a tree (as
opposed to the working directory) with both --untracked
and --no-index. But we traditionally did so by first
collecting the revs, and then complaining when any were
provided.

The --no-index option recently learned to detect revs
much earlier. This has two user-visible effects:

  - we don't bother to resolve revision names at all. So
    when there's a rev/path ambiguity, we always choose to
    treat it as a path.

  - likewise, when you do specify a revision without "--",
    the error you get is "no such path" and not "--untracked
    cannot be used with revs".

The rationale for doing this with --no-index is that it is
meant to be used outside a repository, and so parsing revs
at all does not make sense.

This patch gives --untracked the same treatment. While it
_is_ meant to be used in a repository, it is explicitly
about grepping the non-repository contents. Telling the user
"we found a rev, but you are not allowed to use revs" is
not really helpful compared to "we treated your argument as
a path, and could not find it".

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

If we are using --no-index, then our arguments cannot be
revs in the first place. Not only is it pointless to
diagnose them, but if we are not in a repository, we should
not be trying to resolve any names.

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

We disallow the use of revisions with --no-index, but we
don't actually check and complain until well after we've
parsed the revisions.

This is the cause of a few problems:

 1. We shouldn't be calling get_sha1() at all when we aren't
    in a repository, as it might access the ref or object
    databases. For now, this should generally just return
    failure, but eventually it will become a BUG().

 2. When there's a "--" disambiguator and you're outside a
    repository, we'll complain early with "unable to resolve
    revision". But we can give a much more specific error.

 3. When there isn't a "--" disambiguator, we still do the
    normal rev/path checks. This is silly, as we know we
    cannot have any revs with --no-index. Everything we see
    must be a path.

    Outside of a repository this doesn't matter (since we
    know it won't resolve), but inside one, we may complain
    unnecessarily if a filename happens to also match a
    refname.

This patch skips the get_sha1() call entirely in the
no-index case, and behaves as if it failed (with the
exception of giving a better error message).

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

If we see "git grep pattern rev -- file" then we apply the
usual rev/pathspec disambiguation rules: any "rev" before
the "--" must be a revision, and we do not need to apply the
verify_non_filename() check.

But there are two bugs here:

  1. We keep a seen_dashdash flag to handle this case, but
     we set it in the same left-to-right pass over the
     arguments in which we parse "rev".

     So when we see "rev", we do not yet know that there is
     a "--", and we mistakenly complain if there is a
     matching file.

     We can fix this by making a preliminary pass over the
     arguments to find the "--", and only then checking the rev
     arguments.

  2. If we can't resolve "rev" but there isn't a dashdash,
     that's OK. We treat it like a path, and complain later
     if it doesn't exist.

     But if there _is_ a dashdash, then we know it must be a
     rev, and should treat it as such, complaining if it
     does not resolve. The current code instead ignores it
     and tries to treat it like a path.

This patch fixes both bugs, and tries to comment the parsing
flow a bit better.

It adds tests that cover the two bugs, but also some related
situations (which already worked, but this confirms that our
fixes did not break anything).

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

We loop over the arguments, but every branch of the loop
hits either a "continue" or a "break". Surely we can make
this simpler.

The final conditional is:

  if (arg is a rev) {
	  ... handle rev ...
	  continue;
  }
  break;

We can rewrite this as:

  if (arg is not a rev)
	  break;

  ... handle rev ...

That makes the flow a little bit simpler, and will make
things much easier to follow when we add more logic in
future patches.

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

When running a command of the form

  git grep --no-index pattern -- path

in the absence of a Git repository, an error message will be printed:

  fatal: BUG: setup_git_env called without repository

This is because "git grep" tries to interpret "--" as a rev. "git grep"
has always tried to first interpret "--" as a rev for at least a few
years, but this issue was upgraded from a pessimization to a bug in
commit 59332d1 ("Resurrect "git grep --no-index"", 2010-02-06), which
calls get_sha1 regardless of whether --no-index was specified. This bug
appeared to be benign until commit b1ef400 ("setup_git_env: avoid blind
fall-back to ".git"", 2016-10-20) when Git was taught to die in this
situation.  (This "git grep" bug appears to be one of the bugs that
commit b1ef400 is meant to flush out.)

Therefore, always interpret "--" as signaling the end of options,
instead of trying to interpret it as a rev first.

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

Originally, we set up the threads for grep before parsing
the non-option arguments. In 53b8d931b (grep: disable
threading in non-worktree case, 2011-12-12), the thread code
got bumped lower in the function because it now needed to
know whether we got any revision arguments.

That put a big block of code in between the parsing of revs
and the parsing of pathspecs, both of which share some loop
variables. That makes it harder to read the code than the
original, where the shared loops were right next to each
other.

Let's bump the thread initialization until after all of the
parsing is done.

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

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Doc update.

* nd/rev-list-all-includes-HEAD-doc:
  rev-list-options.txt: update --all about HEAD

Code clean-up.

* rs/fill-directory-optim:
  dir: avoid allocation in fill_directory()