This reworks the diff-tree-helper and show-diff to further make external
diff command interface simpler.
These commands now honor GIT_EXTERNAL_DIFF environment variable which
can point at an arbitrary program that takes 7 parameters:
name file1 file1-sha1 file1-mode file2 file2-sha1 file2-mode
The parameters for an external diff command are as follows:
name this invocation of the command is to emit diff
for the named cache/tree entry.
file1 pathname that holds the contents of the first
file. This can be a file inside the working
tree, or a temporary file created from the blob
object, or /dev/null. The command should not
attempt to unlink it -- the temporary is
unlinked by the caller.
file1-sha1 sha1 hash if file1 is a blob object, or "."
otherwise.
file1-mode mode bits for file1, or "." for a deleted file.
If GIT_EXTERNAL_DIFF environment variable is not set, the
default is to invoke diff with the set of parameters old
show-diff used to use. This built-in implementation honors the
GIT_DIFF_CMD and GIT_DIFF_OPTS environment variables as before.
Signed-off-by: Junio C Hamano <junkio@cox.net> Signed-off-by: Linus Torvalds <torvalds@osdl.org>