The way tree-diff was set up assumed we would use only one set
of pathspec during the entire life of the program.  Move the
pathspec related static variables out to diff_options structure
so that we can filter commits with one set of paths while show
the actual diffs using different set of paths.

I suspect this breaks blame.c, and makes "git log paths..." to
default to the --full-diff, the latter of which is dealt with
the next commit.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

This replaces occurences of "blob", "commit", "tag", and "tree",
where they're really used as type specifiers, which we already
have defined global constants for.
Signed-off-by: NPeter Eriksen <s022018@student.dtu.dk>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

Introduce tree-walk.[ch] and move "struct tree_desc" and
associated functions from various places.

Rename DIFF_FILE_CANON_MODE(mode) macro to canon_mode(mode) and
move it to cache.h.  This macro returns the canonicalized
st_mode value in the host byte order for files, symlinks and
directories -- to be compared with a tree_desc entry.
create_ce_mode(mode) in cache.h is similar but is intended to be
used for index entries (so it does not work for directories) and
returns the value in the network byte order.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

We have operations to "extract" and "update" a "struct tree_desc", but we
only used them in tree-diff.c and they were static to that file.

But other tree traversal functions can use them to their advantage
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

Avoid asking for zero bytes when that change simplifies overall
logic.  Later we would change the wrapper to ask for 1 byte on
platforms that return NULL for zero byte request.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

This makes the tree diff functionality independent of the "git-diff-tree"
program, by splitting the core functionality up into a library file.

This will be needed for when we teach git-rev-list to only follow a
specified set of pathnames, rather than the global revision history.

Most of it is a fairly straightforward code move, but it also involves
some calling convention cleanup, and moving some of the static variables
from diff-tree.c into the options structure.

The actual tree change callback routines also become paramterized by the
diff_options structure, allowing the library functionality to do something
else than just show the diff on stdout.

Right now the only user of this functionality remains git-diff-tree
itself.
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
Signed-off-by: NJunio C Hamano <junkio@cox.net>