Change the type merge_fn_t to accept the array of cache_entry pointers
as const pointers to const pointers.  This documents the fact that the
merge functions don't modify the cache_entry contents or replace any of
the pointers in the array.

Only a single cast is necessary in unpack_nondirectories because adding
two const modifiers at once is not allowed in C.  The cast is safe in
that it doesn't mask any modfication; call_unpack_fn only needs the
array for reading.

Signed-off-by: René Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Add const to struct cache_entry pointers throughout the tree which are
only used for reading.  This allows callers to pass in const pointers.

Signed-off-by: René Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

The diff code represents paths using the diff_filespec
struct. This struct has a sha1 to represent the sha1 of the
content at that path, as well as a sha1_valid member which
indicates whether its sha1 field is actually useful. If
sha1_valid is not true, then the filespec represents a
working tree file (e.g., for the no-index case, or for when
the index is not up-to-date).

The diff_filespec is only used internally, though. At the
interfaces to the diff subsystem, callers feed the sha1
directly, and we create a diff_filespec from it. It's at
that point that we look at the sha1 and decide whether it is
valid or not; callers may pass the null sha1 as a sentinel
value to indicate that it is not.

We should not typically see the null sha1 coming from any
other source (e.g., in the index itself, or from a tree).
However, a corrupt tree might have a null sha1, which would
cause "diff --patch" to accidentally diff the working tree
version of a file instead of treating it as a blob.

This patch extends the edges of the diff interface to accept
a "sha1_valid" flag whenever we accept a sha1, and to use
that flag when creating a filespec. In some cases, this
means passing the flag through several layers, making the
code change larger than would be desirable.

One alternative would be to simply die() upon seeing
corrupted trees with null sha1s. However, this fix more
directly addresses the problem (while bogus sha1s in a tree
are probably a bad thing, it is really the sentinel
confusion sending us down the wrong code path that is what
makes it devastating). And it means that git is more capable
of examining and debugging these corrupted trees. For
example, you can still "diff --raw" such a tree to find out
when the bogus entry was introduced; you just cannot do a
"--patch" diff (just as you could not with any other
corrupted tree, as we do not have any content to diff).

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

The pathspec structure has a few bits of data to drive various operation
modes after we unified the pathspec matching logic in various codepaths.
For example, max_depth field is there so that "git grep" can limit the
output for files found in limited depth of tree traversal. Also in order
to show just the surface level differences in "git diff-tree", recursive
field stops us from descending into deeper level of the tree structure
when it is set to false, and this also affects pathspec matching when
we have wildcards in the pathspec.

The diff-index has always wanted the recursive behaviour, and wanted to
match pathspecs without any depth limit. But we forgot to do so when we
updated tree_entry_interesting() logic to unify the pathspec matching
logic.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

* cn/eradicate-working-copy:
  Remove 'working copy' from the documentation and C code

* jc/diff-index-unpack:
  diff-index: pass pathspec down to unpack-trees machinery
  unpack-trees: allow pruning with pathspec
  traverse_trees(): allow pruning with pathspec

The git term is 'working tree', so replace the most public references
to 'working copy'.

Signed-off-by: Carlos Martín Nieto <cmn@elego.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

And finally, pass the pathspec down through unpack_trees() to traverse_trees()
callchain.

Before and after applying this series, looking for changes in the kernel
repository with a fairly narrow pathspec becomes somewhat faster.

  (without patch)
  $ /usr/bin/time git diff --raw v2.6.27 -- net/ipv6 >/dev/null
  0.48user 0.05system 0:00.53elapsed 100%CPU (0avgtext+0avgdata 163296maxresident)k
  0inputs+952outputs (0major+11163minor)pagefaults 0swaps

  (with patch)
  $ /usr/bin/time git diff --raw v2.6.27 -- net/ipv6 >/dev/null
  0.01user 0.00system 0:00.02elapsed 104%CPU (0avgtext+0avgdata 43856maxresident)k
  0inputs+24outputs (0major+3688minor)pagefaults 0swaps

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

* jc/diff-index-refactor:
  diff-lib: refactor run_diff_index() and do_diff_cache()
  diff-lib: simplify do_diff_cache()

* jc/maint-reset-unmerged-path:
  reset [<commit>] paths...: do not mishandle unmerged paths