clear parsed flag when we free tree buffers

Many code paths will free a tree object's buffer and set it
to NULL after finishing with it in order to keep memory
usage down during a traversal. However, out of 8 sites that
do this, only one actually unsets the "parsed" flag back.
Those sites that don't are setting a trap for later users of
the tree object; even after calling parse_tree, the buffer
will remain NULL, causing potential segfaults.

It is not known whether this is triggerable in the current
code. Most commands do not do an in-memory traversal
followed by actually using the objects again. However, it
does not hurt to be safe for future callers.

In most cases, we can abstract this out to a
"free_tree_buffer" helper. However, there are two
exceptions:

  1. The fsck code relies on the parsed flag to know that we
     were able to parse the object at one point. We can
     switch this to using a flag in the "flags" field.

  2. The index-pack code sets the buffer to NULL but does
     not free it (it is freed by a caller). We should still
     unset the parsed flag here, but we cannot use our
     helper, as we do not want to free the buffer.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
upload-archive: restrict remote objects with reachability check

When serving a remote request, git-upload-archive tries to
restrict access to unreachable objects, which matches the
behavior of upload-pack. However, we did so by restricting
the requested tree to "<ref>[:<path>]", because it is fast.
That covers the common cases, but does not allow requesting
items by a specific sha1 (either a tree or a commit sha1).

Instead, let's do the correct-but-slower method of actually
walking back from the tips to see if the requested object is
reachable. The performance impact of this is roughly:

  1. For a recent commit, the speed is about the same (we
     traverse in reverse chronological order, so we see it
     almost immediately).

  2. For an older commit, even one pointed at directly by a
     ref (e.g., an old tag), we are slower, because we
     traverse from the more recent tips. We are bounded in
     this case by the time to look at all commits (i.e.,
     "time git rev-list --all").

  3. When we see "$ref:$path", we typically perform much
     worse, because our traversal looks at all commits
     first, followed by all trees.

  4. The worst case (which we hit for an unreachable object)
     is equivalent to "time rev-list --objects --all", which
     is about the same amount of time pack-objects spends
     preparing a full clone (which can be in the tens of
     seconds for a large repository).

The implementation is a fairly straightforward application
of the traverse_commit_list function. Using the
mark_objects_reachable function would seem more appropriate,
but it has no mechanism for looking for a specific object,
which lets us end the traversal early in common cases.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
list-objects: optimize "revs->blob_objects = 0" case

If we are traversing trees during a "--objects"
traversal, we may skip blobs if the "blob_objects" field of
rev_info is not set. But we do so as the first thing in
process_blob(), only after we have actually created the
"struct blob" object, incurring a hash lookup. We can
optimize out this no-op call completely.

This does not actually affect any current code, as all of
the current traversals always set blob_objects when looking
at objects, anyway.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
archive: ignore blob objects when checking reachability

We cannot create an archive from a blob object, so we would
not expect anyone to provide one to us. And if they do, we
will fail anyway just after the reachability check.  We can
therefore optimize our reachability check to ignore blobs
completely, and not even create a "struct blob" for them.

Depending on the repository size and the exact place we find
the reachable object in the traversal, this can save 20-25%,
a we can avoid many lookups in the object hash.

The downside of this is that a blob provided to a remote
archive process will fail with "no such object" rather than
"object is not a tree" (we could organize the code to retain
the old message, but since we no longer know whether the
blob is reachable or not, we would potentially be leaking
information about the existence of unreachable objects).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
sequencer: avoid leaking message buffer when refusing to create an empty commit

We should free objects before leaving.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
cherry-pick: add --skip-empty option

Pretty much what it says on the tin.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
cherry-pick: store rewritten commits

Will be useful for the next commits.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
sequencer: run post-rewrite hook

As we should.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Merge branch 'rr/die-on-missing-upstream' into jch

When a reflog notation is used for implicit "current branch", we
did not say which branch and worse said "branch ''".

* rr/die-on-missing-upstream:
  sha1_name: fix error message for @{<N>}, @{<date>}
  sha1_name: fix error message for @{u}
Merge branch 'jk/test-exit-code-by-signal' into jch

j6t <51AEE1C3.9020507@viscovery.net>

* jk/test-exit-code-by-signal:
  t0005: skip signal death exit code test on Windows
  t0005: test git exit code from signal death
Merge branch 'rs/unpack-trees-plug-leak' into jch

* rs/unpack-trees-plug-leak:
  unpack-trees: free cache_entry array members for merges
  diff-lib, read-tree, unpack-trees: mark cache_entry array paramters const
  diff-lib, read-tree, unpack-trees: mark cache_entry pointers const
  unpack-trees: create working copy of merge entry in merged_entry
  unpack-trees: factor out dup_entry
  read-cache: mark cache_entry pointers const
  cache: mark cache_entry pointers const
Merge branch 'tr/test-commit-only-on-orphan' into jch

* tr/test-commit-only-on-orphan:
  Test 'commit --only' after 'checkout --orphan'
Merge branch 'fc/completion-less-ls-remote' into jch

* fc/completion-less-ls-remote:
  completion: avoid ls-remote in certain scenarios
Merge branch 'rj/mingw-cygwin' into jch

Update build for Cygwin 1.[57].  Torsten Bögershausen reports that
this is fine with Cygwin 1.7 ($gmane/225824) so let's try moving it
ahead.

* rj/mingw-cygwin:
  cygwin: Remove the CYGWIN_V15_WIN32API build variable
  mingw: rename WIN32 cpp macro to GIT_WINDOWS_NATIVE
Merge branch 'fc/remote-hg' into jch

* fc/remote-hg: (50 commits)
  remote-hg: add support for --force
  remote-hg: add support for --dry-run
  remote-hg: check if a fetch is needed
  remote-hg: trivial cleanup
  remote-helpers: improve marks usage
  remote-hg: add check_push() helper
  remote-hg: add setup_big_push() helper
  remote-hg: remove files before modifications
  remote-hg: improve lightweight tag author
  remote-hg: use remote 'default' not local one
  remote-hg: improve branch listing
  remote-hg: simplify branch_tip()
  remote-hg: check diverged bookmarks
  remote-hg: pass around revision refs
  remote-hg: implement custom checkheads()
  remote-hg: implement custom push()
  remote-hg: only update necessary revisions
  remote-hg: force remote bookmark push selectively
  remote-hg: reorganize bookmark handling
  remote-hg: add test for failed double push
  ...
Merge branch 'fc/remote-bzr' into jch

* fc/remote-bzr:
  remote-bzr: add fallback check for a partial clone
  remote-bzr: reorganize the way 'wanted' works
  remote-bzr: trivial cleanups
  remote-bzr: change global repo
  remote-bzr: delay cloning/pulling
  remote-bzr: simplify get_remote_branch()
  remote-bzr: fix for files with spaces
  remote-bzr: recover from failed clones
Merge branch 'fc/do-not-use-the-index-in-add-to-index' into jch

* fc/do-not-use-the-index-in-add-to-index:
  read-cache: trivial style cleanups
  read-cache: fix wrong 'the_index' usage
Merge branch 'xq/credential-osxkeychain' into jch

* xq/credential-osxkeychain:
  credential-osxkeychain: support more protocols
Merge branch 'cb/log-follow-with-combined' into jch

* cb/log-follow-with-combined:
  fix segfault with git log -c --follow
Merge branch 'mm/mediawiki-https-fail-message' into jch

Hint users when https:// connection failed to check the
certificate; it is a good hint if we assumie that it is common
error for the end users to make.

* mm/mediawiki-https-fail-message:
  git-remote-mediawiki: better error message when HTTP(S) access fails