t5004: avoid using tar for checking emptiness of archive

Test 2 of t5004 checks if a supposedly empty tar archive really
contains no files.  24676f02 (t5004: fix issue with empty archive test
and bsdtar) removed our commit hash to make it work with bsdtar, but
the test still fails on NetBSD and OpenBSD, which use their own tar
that considers a tar file containing only NULs as broken.

Here's what the different archivers do when asked to create a tar
file without entries:

	$ uname -v
	NetBSD 6.0.1 (GENERIC)
	$ gtar --version | head -1
	tar (GNU tar) 1.26
	$ bsdtar --version
	bsdtar 2.8.4 - libarchive 2.8.4

	$ : >zero.tar
	$ perl -e 'print "\0" x 10240' >tenk.tar
	$ sha1 zero.tar tenk.tar
	SHA1 (zero.tar) = da39a3ee5e6b4b0d3255bfef95601890afd80709
	SHA1 (tenk.tar) = 34e163be8e43c5631d8b92e9c43ab0bf0fa62b9c

	$ : | tar cf - -T - | sha1
	da39a3ee5e6b4b0d3255bfef95601890afd80709
	$ : | gtar cf - -T - | sha1
	34e163be8e43c5631d8b92e9c43ab0bf0fa62b9c
	$ : | bsdtar cf - -T - | sha1
	34e163be8e43c5631d8b92e9c43ab0bf0fa62b9c

So NetBSD's native tar creates an empty file, while GNU tar and bsdtar
both give us 10KB of NULs -- just like git archive with an empty tree.
Now let's see how the archivers handle these two kinds of empty tar
files:

	$ tar tf zero.tar; echo $?
	tar: Unexpected EOF on archive file
	1
	$ gtar tf zero.tar; echo $?
	gtar: This does not look like a tar archive
	gtar: Exiting with failure status due to previous errors
	2
	$ bsdtar tf zero.tar; echo $?
	0

	$ tar tf tenk.tar; echo $?
	tar: Cannot identify format. Searching...
	tar: End of archive volume 1 reached
	tar: Sorry, unable to determine archive format.
	$ gtar tf tenk.tar; echo $?
	0
	$ bsdtar tf tenk.tar; echo $?
	0

NetBSD's tar complains about both, bsdtar happily accepts any of them
and GNU tar doesn't like zero-length archive files.  So the safest
course of action is to stay with our block-of-NULs format which is
compatible with GNU tar and bsdtar, as we can't make NetBSD's native
tar happy anyway.

We can simplify our test, however, by taking tar out of the picture.
Instead of extracting the archive and checking for the non-presence of
files, check if the file has a size of 10KB and contains only NULs.
This makes t5004 pass on NetBSD and OpenBSD.

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
t5004: resurrect original empty tar archive test

Add a test to verify the emptiness of an archive by extracting its
contents.  Don't run this test if the version of tar doesn't support
archives containing only a comment header, though.

The existing check 'tar archive of empty tree is empty' used to work
like that (minus the tar capability check) but was changed to depend
on the exact representation of empty tar files created by git archive
instead of on the behaviour of tar in order to avoid issues with
different tar versions.

The different approaches test different things: The existing one is
for empty trees, for which we know the exact expected output and thus
we can simply check it without extracting; the new one is for commits
with empty trees, whose archives include stamps and so the more
"natural" check by extraction is a better fit because it focuses on
the interesting aspect, namely the absence of any archive entries.

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Merge branch 'fc/transport-helper-error-reporting' into jch

Update transport helper to report errors and maintain ref hierarchy
used to keep track of remote helper state better.

* fc/transport-helper-error-reporting:
  t5801: "VAR=VAL shell_func args" is forbidden
  transport-helper: update remote helper namespace
  transport-helper: trivial code shuffle
  transport-helper: warn when refspec is not used
  transport-helper: clarify pushing without refspecs
  transport-helper: update refspec documentation
  transport-helper: clarify *:* refspec
  transport-helper: improve push messages
  transport-helper: mention helper name when it dies
  transport-helper: report errors properly

# Conflicts:
# 	t/t5801-remote-helpers.sh
Merge branch 'js/transport-helper-error-reporting-fix' into jch

Finishing touches to fc/transport-helper-error-reporting topic.

* js/transport-helper-error-reporting-fix:
  git-remote-testgit: build it to run under $SHELL_PATH
  git-remote-testgit: further remove some bashisms
  git-remote-testgit: avoid process substitution
Merge branch 'mh/fetch-into-shallow' into jch

* mh/fetch-into-shallow:
  t5500: add test for fetching with an unknown 'shallow'
  upload-pack: ignore 'shallow' lines with unknown obj-ids
Merge branch 'tr/line-log' into jch

* tr/line-log:
  git-log(1): remove --full-line-diff description
  line-log: fix documentation formatting
  log -L: improve comments in process_all_files()
  log -L: store the path instead of a diff_filespec
  log -L: test merge of parallel modify/rename
  t4211: pass -M to 'git log -M -L...' test
  log -L: fix overlapping input ranges
  log -L: check range set invariants when we look it up
  Speed up log -L... -M
  log -L: :pattern:file syntax to find by funcname
  Implement line-history search (git log -L)
  Export rewrite_parents() for 'log -L'
  Refactor parse_loc

# Conflicts:
# 	Documentation/git-log.txt
# 	log-tree.c
Merge branch 'jc/prune-all' into jch

We used the approxidate() parser for "--expire=<timestamp>" options
of various commands, but it is better to treat --expire=all and
--expire=now a bit more specially than using the current timestamp.
Update "git gc" and "git reflog" with a new parsing function for
expiry dates.

* jc/prune-all:
  prune: introduce OPT_EXPIRY_DATE() and use it
  api-parse-options.txt: document "no-" for non-boolean options
  git-gc.txt, git-reflog.txt: document new expiry options
  date.c: add parse_expiry_date()
Merge branch 'jl/submodule-mv' into jch

"git mv A B" when moving a submodule A does "the right thing",
inclusing relocating its working tree and adjusting the paths in
the .gitmodules file.

* jl/submodule-mv:
  submodule.c: duplicate real_path's return value
  rm: delete .gitmodules entry of submodules removed from the work tree
  Teach mv to update the path entry in .gitmodules for moved submodules
  Teach mv to move submodules using a gitfile
  Teach mv to move submodules together with their work trees
Merge branch 'jk/submodule-subdirectory-ok' into jch

Allow various subcommands of "git submodule" to be run not from the
top of the working tree of the superproject.

* jk/submodule-subdirectory-ok:
  submodule: fix quoting in relative_path()
  submodule: drop the top-level requirement
  rev-parse: add --prefix option
Merge branch 'jh/checkout-auto-tracking' into jch

Updates "git checkout foo" that DWIMs the intended "upstream" and
turns it into "git checkout -t -b foo remotes/origin/foo" to
correctly take existing remote definitions into account.  The
remote "origin" may be what uniquely map its own branch to
remotes/some/where/foo but that some/where may not be "origin".

* jh/checkout-auto-tracking:
  glossary: Update and rephrase the definition of a remote-tracking branch
  branch.c: Validate tracking branches with refspecs instead of refs/remotes/*
  t9114.2: Don't use --track option against "svn-remote"-tracking branches
  t7201.24: Add refspec to keep --track working
  t3200.39: tracking setup should fail if there is no matching refspec.
  checkout: Use remote refspecs when DWIMming tracking branches
  t2024: Show failure to use refspec when DWIMming remote branch names
  t2024: Add tests verifying current DWIM behavior of 'git checkout <branch>'
Merge branch 'as/check-ignore' into jch

Enhance "check-ignore" (1.8.2 update) to work more like "check-attr"
over bidi-pipes.

* as/check-ignore:
  t0008: use named pipe (FIFO) to test check-ignore streaming
  Documentation: add caveats about I/O buffering for check-{attr,ignore}
  check-ignore: allow incremental streaming of queries via --stdin
  check-ignore: move setup into cmd_check_ignore()
  check-ignore: add -n / --non-matching option
  t0008: remove duplicated test fixture data

# Conflicts:
# 	builtin/check-ignore.c
Merge branch 'mh/packed-refs-various' into jch

Updates reading and updating packed-refs file, correcting corner
case bugs.

* mh/packed-refs-various: (33 commits)
  refs: handle the main ref_cache specially
  refs: change do_for_each_*() functions to take ref_cache arguments
  pack_one_ref(): do some cheap tests before a more expensive one
  pack_one_ref(): use write_packed_entry() to do the writing
  pack_one_ref(): use function peel_entry()
  refs: inline function do_not_prune()
  pack_refs(): change to use do_for_each_entry()
  refs: use same lock_file object for both ref-packing functions
  pack_one_ref(): rename "path" parameter to "refname"
  pack-refs: merge code from pack-refs.{c,h} into refs.{c,h}
  pack-refs: rename handle_one_ref() to pack_one_ref()
  refs: extract a function write_packed_entry()
  repack_without_ref(): write peeled refs in the rewritten file
  t3211: demonstrate loss of peeled refs if a packed ref is deleted
  refs: change how packed refs are deleted
  search_ref_dir(): return an index rather than a pointer
  repack_without_ref(): silence errors for dangling packed refs
  t3210: test for spurious error messages for dangling packed refs
  refs: change the internal reference-iteration API
  refs: extract a function peel_entry()
  ...
Merge branch 'rj/sparse' into jch

* rj/sparse:
  sparse: Fix mingw_main() argument number/type errors
  compat/mingw.c: Fix some sparse warnings
  compat/win32mmap.c: Fix some sparse warnings
  compat/poll/poll.c: Fix a sparse warning
  compat/win32/pthread.c: Fix a sparse warning
  compat/unsetenv.c: Fix a sparse warning
  compat/nedmalloc: Fix compiler warnings on linux
  compat/nedmalloc: Fix some sparse warnings
  compat/fnmatch/fnmatch.c: Fix a sparse error
  compat/regex/regexec.c: Fix some sparse warnings
Merge branch 'jk/test-output' into jch

When TEST_OUTPUT_DIRECTORY setting is used, it was handled somewhat
inconsistently between the test framework and t/Makefile, and logic
to summarize the results looked at a wrong place.

* jk/test-output:
  t/Makefile: don't define TEST_RESULTS_DIRECTORY recursively
  test output: respect $TEST_OUTPUT_DIRECTORY
  t/Makefile: fix result handling with TEST_OUTPUT_DIRECTORY
Merge branch 'jk/subtree-do-not-push-if-split-fails' into jch

"git subtree" (in contrib/) had one codepath with loose error
checks to lose data at the remote side.

* jk/subtree-do-not-push-if-split-fails:
  contrib/subtree: don't delete remote branches if split fails
Merge branch 'jk/lookup-object-prefer-latest' into jch

Optimizes object lookup when the object hashtable starts to become
crowded.

* jk/lookup-object-prefer-latest:
  lookup_object: prioritize recently found objects
Merge branch 'jn/config-ignore-inaccessible' into jch

When $HOME is misconfigured to point at an unreadable directory, we
used to complain and die. This loosens the check.

* jn/config-ignore-inaccessible:
  config: allow inaccessible configuration under $HOME
### match next
Merge branch 'fc/completion' into jch

I saw this discussed somewhat. Is everybody happy with this
version?  This is its v2, in the $gmane/222682 thread.

* fc/completion:
  completion: remove __git_index_file_list_filter()
  completion: add space after completed filename
  completion: add hack to enable file mode in bash < 4
  completion: refactor __git_complete_index_file()
  completion: refactor diff_index wrappers
  completion: use __gitcompadd for __gitcomp_file
  completion; remove unuseful comments
  completion: document tilde expansion failure in tests
  completion: add file completion tests
Merge branch 'fc/zsh-leftover-bits' into jch

* fc/zsh-leftover-bits:
  completion: synchronize zsh wrapper
  completion: cleanup zsh wrapper