git-rebase: make 'rebase HEAD branch' work as expected.
When you want to amend the commit message of 3 commits before
the tip of the current branch, say 'master',
A--B--C--D--E(master)
it is sometimes handy to make your head detached at that commit
with:
$ git checkout HEAD~3 ;# check out B
$ git commit --amend ;# without modifying contents...
to create:
.B'(HEAD)
/
A--B--C--D--E(master)
and then rebase 'master' branch onto HEAD with this:
$ git rebase HEAD master
to result in:
.B'-C'-D'-E(master=HEAD)
/
A--B--C--D--E
However, the current code interprets HEAD after it switches to
the branch 'master', which means the rebase will not do
anything. You have to say something unwieldly like this
instead:
$ git rebase $(git rev-parse HEAD) master
This fixes it by expanding the $onto commit name before
switching to the target branch.
tree_entry_interesting(): allow it to say "everything is interesting"
In addition to optimizing pathspecs that would never match,
which was done earlier, this optimizes pathspecs that would
always match (e.g. "arch/" while the traversal is already in
"arch/i386/" hierarchy).
This patch makes the worst case slightly more palatable, while
improving average case.
If we already know that some of the pathspecs can match later
entries in the tree we are looking at, we do not have to do more
expensive strncmp() upfront before comparing the length of the
match pattern and the path, as a path longer than the match
pattern will not match it, and a path shorter than the match
pattern will match only if the path is a directory-component
wise prefix of the match pattern.
Teach tree_entry_interesting() that the tree entries are sorted.
When we are looking at a tree entry with pathspecs, if all the
pathspecs sort strictly earlier than the entry we are currently
looking at, there is no way later entries in the same tree would
match our pathspecs, because the entries are sorted.
Switch over tree descriptors to contain a pre-parsed entry
This makes the tree descriptor contain a "struct name_entry" as part of
it, and it gets filled in so that it always contains a valid entry. On
some benchmarks, it improves performance by up to 15%.
That makes tree entry "extract" trivial, and means that we only actually
need to decode each tree entry just once: we decode the first one when
we initialize the tree descriptor, and each subsequent one when doing
"update_tree_entry()". In particular, this means that we don't need to
do strlen() both at extract time _and_ at update time.
Finally, it also allows more sharing of code (entry_extract(), that
wanted a "struct name_entry", just got totally trivial, along with the
"tree_entry()" function).
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
Initialize tree descriptors with a helper function rather than by hand.
This removes slightly more lines than it adds, but the real reason for
doing this is that future optimizations will require more setup of the
tree descriptor, and so we want to do it in one place.
Also renamed the "desc.buf" field to "desc.buffer" just to trigger
compiler errors for old-style manual initializations, making sure I
didn't miss anything.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
Since we have the "tree_entry_len()" helper function these days, and
don't need to do a full strlen(), there's no point in saving the path
length - it's just redundant information.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
[PATCH] prefer "git COMMAND" over "git-COMMAND" in gitk
Preferring git _space_ COMMAND over git _dash_ COMMAND allows the
user to have only git and gitk in their path. e.g. when git and gitk
are symbolic links in a personal bin directory to the real git and gitk.
The earlier round makes the function return "is it different"
and it does not return a value suitable for sorting anymore. Reverse
the logic to return "are they the same suspect" instead, and rename
it to "same_suspect()".
When creating a new object, we use "deflate(stream, Z_FINISH)" in a loop
until it no longer returns Z_OK, and then we do "deflateEnd()" to finish
up business.
That should all work, but the fact is, it's not how you're _supposed_ to
use the zlib return values properly:
- deflate() should never return Z_OK in the first place, except if we
need to increase the output buffer size (which we're not doing, and
should never need to do, since we pre-allocated a buffer that is
supposed to be able to hold the output in full). So the "while()" loop
was incorrect: Z_OK doesn't actually mean "ok, continue", it means "ok,
allocate more memory for me and continue"!
- if we got an error return, we would consider it to be end-of-stream,
but it could be some internal zlib error. In short, we should check
for Z_STREAM_END explicitly, since that's the only valid return value
anyway for the Z_FINISH case.
- we never checked deflateEnd() return codes at all.
Now, admittedly, none of these issues should ever happen, unless there is
some internal bug in zlib. So this patch should make zero difference, but
it seems to be the right thing to do.
We should probablybe anal and check the return value of "deflateInit()"
too!
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
Don't ever return corrupt objects from "parse_object()"
Looking at the SHA1 validation code due to the corruption that Alexander
Litvinov is seeing under Cygwin, I notice that one of the most central
places where we read objects, we actually do end up verifying the SHA1 of
the result, but then we happily parse it anyway.
And using "printf" to write the error message means that it not only can
get lost, but will actually mess up stdout, and cause other strange and
hard-to-debug failures downstream.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
When appending objects to a pack, make sure the appended data is really
what we expect instead of simply loading potentially corrupted objects
and legitimating them by computing a SHA1 of that corrupt data.
With this the sha1_object() can lose its test_for_collision parameter
which is now redundent.
Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
don't ever allow SHA1 collisions to exist by fetching a pack
Waaaaaaay back Git was considered to be secure as it never overwrote
an object it already had. This was ensured by always unpacking the
packfile received over the network (both in fetch and receive-pack)
and our already existing logic to not create a loose object for an
object we already have.
Lately however we keep "large-ish" packfiles on both fetch and push
by running them through index-pack instead of unpack-objects. This
would let an attacker perform a birthday attack.
How? Assume the attacker knows a SHA-1 that has two different
data streams. He knows the client is likely to have the "good"
one. So he sends the "evil" variant to the other end as part of
a "large-ish" packfile. The recipient keeps that packfile, and
indexes it. Now since this is a birthday attack there is a SHA-1
collision; two objects exist in the repository with the same SHA-1.
They have *very* different data streams. One of them is "evil".
Currently the poor recipient cannot tell the two objects apart,
short of by examining the timestamp of the packfiles. But lets
say the recipient repacks before he realizes he's been attacked.
We may wind up packing the "evil" version of the object, and deleting
the "good" one. This is made *even more likely* by Junio's recent
rearrange_packed_git patch (b867092f).
It is extremely unlikely for a SHA1 collisions to occur, but if it
ever happens with a remote (hence untrusted) object we simply must
not let the fetch succeed.
Normally received packs should not contain objects we already have.
But when they do we must ensure duplicated objects with the same SHA1
actually contain the same data.
Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
The configured refspecs are printed almost verbatim, i.e. both the local
and the remote branch name separated by a colon are printed; only the
prefix 'refs/heads/' is removed, like this:
Local branch(es) pushed with 'git push'
master refs/tags/*:refs/tags/* next:next
Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at> Signed-off-by: Junio C Hamano <junkio@cox.net>
The thing is, if the output buffer is empty, we should *still* actually
use the zlib routines to *unpack* that empty output buffer.
But we had a test that said "only unpack if we still expect more output".
So we wouldn't use up all the zlib stream, because we felt that we didn't
need it, because we already had all the bytes we wanted. And it was
"true": we did have all the output data. We just needed to also eat all
the input data!
We've had this bug before - thinking that we don't need to inflate()
anything because we already had it all..
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
contrib/continuous: a continuous integration build manager
This is a simple but powerful continuous integration build system
for Git. It works by receiving push events from repositories
through the post-receive hook, aggregates them on a per-branch
basis into a first-come-first-serve build queue, and lets a
background build daemon perform builds one at a time.
Signed-off-by: Shawn O. Pearce <spearce@spearce.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
Provide some technical documentation for shallow clones
There has not been any work on the shallow stuff lately, so it is hard
to find out what it does, and how. This document describes the ideas
as well as the current problems, and can serve as a starting point for
shallow people.
Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de> Signed-off-by: Junio C Hamano <junkio@cox.net>
xdiff/xutils.c(xdl_hash_record): factor out whitespace handling
Since in at least one use case, xdl_hash_record() takes over 15% of the
CPU time, it makes sense to even micro-optimize it. For many cases, no
whitespace special handling is needed, and in these cases we should not
even bother to check for whitespace in _every_ iteration of the loop.
Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de> Signed-off-by: Junio C Hamano <junkio@cox.net>
The commit structures are guaranteed their uniqueness by the object
layer, so we can check their address and see if they are the same
without going down to the object sha1 level.
use a LRU eviction policy for the delta base cache
This provides a smoother degradation in performance when the cache
gets trashed due to the delta_base_cache_limit being reached. Limited
testing with really small delta_base_cache_limit values appears to confirm
this.
Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
Currently there are 3 different ways to deal with the cache size.
Let's stick to only one. The compiler is smart enough to produce the exact
same code in those cases anyway.
Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
This is mainly just a cleanup patch, and sets up for later changes where
the tree-diff.c "interesting()" function can return more than just a
yes/no value.
In particular, it should be quite possible to say "no subsequent entries
in this tree can possibly be interesting any more", and thus allow the
callers to short-circuit the tree entirely.
In fact, changing the callers to do so is trivial, and is really all this
patch really does, because changing "interesting()" itself to say that
nothing further is going to be interesting is definitely more complicated,
considering that we may have arbitrary pathspecs.
But in cleaning up the callers, this actually fixes a potential small
performance issue in diff_tree(): if the second tree has a lot of
uninterestign crud in it, we would keep on doing the "is it interesting?"
check on the first tree for each uninteresting entry in the second one.
The answer is obviously not going to change, so that was just not helping.
The new code is clearer and simpler and avoids this issue entirely.
I also renamed "interesting()" to "tree_entry_interesting()", because I
got frustrated by the fact that
- we actually had *another* function called "interesting()" in another
file, and I couldn't tell from the profiles which one was the one that
mattered more.
- when rewriting it to return a ternary value, you can't just do
if (interesting(...))
...
any more, but want to assign the return value to a local variable. The
name of choice for that variable would normally be "interesting", so
I just wanted to make the function name be more specific, and avoid
that whole issue (even though I then didn't choose that name for either
of the users, just to avoid confusion in the patch itself ;)
In other words, this doesn't really change anything, but I think it's a
good thing to do, and if somebody comes along and writes the logic for
"yeah, none of the pathspecs you have are interesting", we now support
that trivially.
It could easily be a meaningful optimization for things like "blame",
where there's just one pathspec, and stopping when you've seen it would
allow you to avoid about 50% of the tree traversals on average.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
This makes "track_tree_refs()" use the same "tree_entry()" function for
counting the entries as it does for actually traversing them a few lines
later.
Not a biggie, but the reason I care was that this was the only user of
"update_tree_entry()" that didn't actually *extract* the tree entry first.
It doesn't matter as things stand now, but it meant that a separate
test-patch I had that avoided a few more "strlen()" calls by just saving
the entry length in the entry descriptor and using it directly when
updating wouldn't work without this patch.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
The new configuration variable core.deltaBaseCacheLimit allows the
user to control how much memory they are willing to give to Git for
caching base objects of deltas. This is not normally meant to be
a user tweakable knob; the "out of the box" settings are meant to
be suitable for almost all workloads.
We default to 16 MiB under the assumption that the cache is not
meant to consume all of the user's available memory, and that the
cache's main purpose was to cache trees, for faster path limiters
during revision traversal. Since trees tend to be relatively small
objects, this relatively small limit should still allow a large
number of objects.
On the other hand we don't want the cache to start storing 200
different versions of a 200 MiB blob, as this could easily blow
the entire address space of a 32 bit process.
We evict OBJ_BLOB from the cache first (credit goes to Junio) as
we want to favor OBJ_TREE within the cache. These are the objects
that have the highest inflate() startup penalty, as they tend to
be small and thus don't have that much of a chance to ammortize
that penalty over the entire data.
Signed-off-by: Shawn O. Pearce <spearce@spearce.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
* sp/run-command:
Use run_command within send-pack
Use run_command within receive-pack to invoke index-pack
Use run_command within merge-index
Use run_command for proxy connections
Use RUN_GIT_CMD to run push backends
Correct new compiler warnings in builtin-revert
Replace fork_with_pipe in bundle with run_command
Teach run-command to redirect stdout to /dev/null
Teach run-command about stdout redirection
In the Linux kernel, for example, it's common to include Cc: lines
for cases when you want to remember to cc someone on a patch without
necessarily claiming they signed off on it. Make git-send-email
aware of these.
Signed-off-by: "J. Bruce Fields" <bfields@citi.umich.edu> Signed-off-by: Junio C Hamano <junkio@cox.net>
user-manual: introduce "branch" and "branch head" differently
I was using "branch" to mean "head", but that's perhaps a little
sloppy; so instead start by using the terms "branch head" and "head",
while still quickly falling back on "branch", since that's what
people actually say more frequently.
Also include glossary references on the first uses of "head" and "tag".
Signed-off-by: "J. Bruce Fields" <bfields@citi.umich.edu>
The sort_glossary.pl script sorts the glossary, checks for duplicates,
and automatically adds cross-references.
But it's not so hard to do all that by hand, and sometimes the automatic
cross-references are a little wrong; so let's run the script one last
time and check in its output.
Note: to make the output fit better into the user manual I also deleted
the acknowledgements at the end, which was maybe a little rude; feel
free to object and I can find a different solution.
Cc: Johannes Schindelin <Johannes.Schindelin@gmx.de> Signed-off-by: "J. Bruce Fields" <bfields@citi.umich.edu>
user-manual: Use def_ instead of ref_ for glossary references.
I'd like to start using references to the glossary in the user manual.
The "ref_" prefix for these references seems a little generic; so
replace with "def_".
Signed-off-by: "J. Bruce Fields" <bfields@citi.umich.edu>
The --nonet option prevents xsltproc from going to the network to find
anything. But it always tries to find them locally first, so for a
user with the necessary docbook stylesheets installed the build will
work just fine without xsltproc attempting to use the network; all
--nonet does is make it fail rather than falling back on that. That
doesn't seem particularly helpful.
Signed-off-by: "J. Bruce Fields" <bfields@citi.umich.edu>
* ar/diff:
Add tests for --quiet option of diff programs
try-to-simplify-commit: use diff-tree --quiet machinery.
revision.c: explain what tree_difference does
Teach --quiet to diff backends.
diff --quiet
Remove unused diffcore_std_no_resolve
Allow git-diff exit with codes similar to diff(1)
This is a micro-optimization that grew out of the mailing list discussion
about "strlen()" showing up in profiles.
We used to pass regular C strings around to the low-level tree walking
routines, and while this worked fine, it meant that we needed to call
strlen() on strings that the caller always actually knew the size of
anyway.
So pass the length of the string down wih the string, and avoid
unnecessary calls to strlen(). Also, when extracting a pathname from a
tree entry, use "tree_entry_len()" instead of strlen(), since the length
of the pathname is directly calculable from the decoded tree entry itself
without having to actually do another strlen().
This shaves off another ~5-10% from some loads that are very tree
intensive (notably doing commit filtering by a pathspec).
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>" Signed-off-by: Junio C Hamano <junkio@cox.net>
A malloc() + memcpy() will always be faster than mmap() +
malloc() + inflate(). If the data is already there it is
certainly better to copy it straight away.
With this patch below I can do 'git log drivers/scsi/ >
/dev/null' about 7% faster. I bet it might be even more on
those platforms with bad mmap() support.
Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
Especially with the new index format to come, it is more appropriate
to encapsulate more into check_packed_git_idx() and assume less of the
index format in struct packed_git.
To that effect, the index_base is renamed to index_data with void * type
so it is not used directly but other pointers initialized with it. This
allows for a couple pointer cast removal, as well as providing a better
generic name to grep for when adding support for new index versions or
formats.
And index_data is declared const too while at it.
Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
The 'use packed deltified objects' test was flawed as it failed to
remove the pack and index from the previous test, effectively preventing
the desired pack from being exercised as objects could be found in that
other pack instead.
Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
Such a builtin remote simplifies the operation of "git-fetch",
which will populate FETCH_HEAD but will not pretend that two
repositories are in use, will not create a thin pack, and will
not perform any useless remapping of names. The speed
improvement is around 20%, and it should improve more if
"git-fetch" is converted to a builtin.
To this end, git-parse-remote is grown with a new kind of
remote, 'builtin'. In git-fetch.sh, we treat the builtin remote
specially in that it needs no pack/store operations. In fact,
doing git-fetch on a builtin remote will simply populate
FETCH_HEAD appropriately.
The patch also improves of the --track/--no-track support,
extending it so that branch.<name>.remote items referring '.'
can be created. Finally, it fixes a typo in git-checkout.sh.
Signed-off-by: Paolo Bonzini <bonzini@gnu.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
git-log --first-parent: show only the first parent log
If your development history does not have fast-forward merges,
i.e. the "first parent" of commits in your history are special
than other parents, this option gives a better overview of the
evolution of a particular branch.
try-to-simplify-commit: use diff-tree --quiet machinery.
This uses diff-tree --quiet machinery to terminate the internal
diff-tree between a commit and its parents via revs.pruning (not
revs.diffopt) as soon as we find enough about the tree change.
With respect to the optionally given pathspec, we are interested
if the tree of commit is identical to the parent's, only adds
new paths to the parent's, or there are other differences. As
soon as we find out that there is one such other kind of
difference, we do not have to compare the rest of the tree.
Because we do not call standard diff_addremove/diff_change, we
instruct the diff-tree machinery to stop early by setting
has_changes when we say we found the trees to be different.
This adds the command line option 'quiet' to tell 'git diff-*'
that we are not interested in the actual diff contents but only
want to know if there is any change. This option automatically
turns --exit-code on, and turns off output formatting, as it
does not make much sense to show the first hit we happened to
have found.
The --quiet option is silently turned off (but --exit-code is
still in effect, so is silent output) if postprocessing filters
such as pickaxe and diff-filter are used. For all practical
purposes I do not think of a reason to want to use these filters
and not viewing the diff output.
The backends have not been taught about the option with this patch.
That is a topic for later rounds.
This introduces a new command-line option: --exit-code. The diff
programs will return 1 for differences, return 0 for equality, and
something else for errors.
Signed-off-by: Alex Riesen <raa.lkml@gmail.com> Signed-off-by: Junio C Hamano <junkio@cox.net>
Previous formulation could make it appear as removing all lines
matching a regexp (at least, I was looking for such a flag, and
confused this flag for what I was looking for).
Signed-off-by: Yann Dirson <ydirson@altern.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
git-checkout: fix "eval" used for merge labelling.
The symbolic notation of the fork point can contain whitespaces (e.g.
"git checkout -m 'HEAD@{9 hours ago}'"). Quote strings properly
when using eval to prepare GITHEAD_$new
update-hook: fix incorrect use of git-describe and sed for finding previous tag
Previously git-describe would output lines of the form v1.1.1-gf509d56
The update hook found the dash and stripped it off using
sed 's/-g.*//'
The remainder was then used as the previous tag name.
However, git-describe has changed format. The output is now of the form v1.1.1-23-gf509d56
The above sed fragment doesn't strip the middle "-23", and so the
previous tag name used would be "v1.1.1-23". This is incorrect.
Since the hook script was written, git-describe now gained support for
"--abbrev=0", which it uses as a special flag to tell it not to output
anything other than the nearest tag name. This patch fixes the problem,
and prevents any future recurrence by using this new flag rather than
sed to find the previous tag.
Signed-off-by: Andy Parkins <andyparkins@gmail.com> Signed-off-by: Junio C Hamano <junkio@cox.net>
cvsserver: further improve messages on commit and status
commit: Also print the old revision similar to how cvs does it and
prepend a line stating the filename so that one can actually
understand what happened when commiting more than one file.
status: Fix the RCS filename displayed. The directory was
printed twice.
Signed-off-by: Frank Lichtenheld <frank@lichtenheld.de> Signed-off-by: Junio C Hamano <junkio@cox.net>
* jc/fetch:
.gitignore: add git-fetch--tool
builtin-fetch--tool: fix reflog notes.
git-fetch: retire update-local-ref which is not used anymore.
builtin-fetch--tool: make sure not to overstep ls-remote-result buffer.
fetch--tool: fix uninitialized buffer when reading from stdin
builtin-fetch--tool: adjust to updated sha1_object_info().
git-fetch--tool takes flags before the subcommand.
Use stdin reflist passing in git-fetch.sh
Use stdin reflist passing in parse-remote
Allow fetch--tool to read from stdin
git-fetch: rewrite expand_ref_wildcard in C
git-fetch: rewrite another shell loop in C
git-fetch: move more code into C.
git-fetch--tool: start rewriting parts of git-fetch in C.
git-fetch: split fetch_main into fetch_dumb and fetch_native
If you use scanf or sscanf to parse integers, your code probably
accepts bogus inputs. For example, builtin-grep (aka git-grep) uses
sscanf(scan, "%u", &num) to parse the integer argument to -A, -B, -C.
Currently, "-C 1,000" and "-C 4294967297" are both treated just like
"-C 1":
$ git-grep -h -C 4294967297 juggle
out and you may find it easier to switch back and forth if you
juggle multiple lines of development simultaneously. Of
course, you will pay the price of more disk usage to hold
The obvious fix is to use strtoul instead. But using a bare strtoul is
too messy, at least when done properly, so I've added a wrapper function.
The new function in the patch below belongs elsewhere if it would be
useful in replacing any of the four remaining uses of sscanf.
One final note: With this change, I get a slightly different
diagnostic depending on the context size:
A common convention that makes it easy to identify the source
of a diagnostic is to include the program name before the first ":".
Whether that should be "git" or "git-grep" is another question.
Using "grep" or "fatal" is misleading.
Signed-off-by: Jim Meyering <jim@meyering.net> Signed-off-by: Junio C Hamano <junkio@cox.net>
shortlog: prompt when reading from terminal by mistake
I was trying to see who have been active recently to find GSoC
mentor candidates by running:
$ git shortlog -s -n --since=4.months | head -n 20
After waiting for about 20 seconds, I started getting worried,
thinking that the recent revision traversal updates might have
had an unintended side effect.
Not so. "git shortlog" acts as a filter when no revs are given,
unlike "git log" which defaults to HEAD. It was reading from
its standard input.
git-svn: add -l/--local command to "git svn rebase"
This avoids fetching new revisions remotely, and is usefuly
versus plain "git rebase" because the user does not have to
specify which remote head to rebase against.
Signed-off-by: Eric Wong <normalperson@yhbt.net> Signed-off-by: Junio C Hamano <junkio@cox.net>
Add git-mergetool to run an appropriate merge conflict resolution program
The git-mergetool program can be used to automatically run an appropriate
merge resolution program to resolve merge conflicts. It will automatically
run one of kdiff3, tkdiff, meld, xxdiff, or emacs emerge programs.
Maybe unnecessary as the merge-index utility may go away in the
future, but its currently here, its shorter to use run_command,
and probably will help the MinGW port out.
Signed-off-by: Shawn O. Pearce <spearce@spearce.org> Signed-off-by: Junio C Hamano <junkio@cox.net>