2cf565c53c
Split the core-git.txt file Formatting fix to the diff-format.txt Signed-off-by: David Greaves <david@dgreaves.com>
151 lines
5.2 KiB
Plaintext
151 lines
5.2 KiB
Plaintext
git-read-tree(1)
|
|
================
|
|
v0.1, May 2005
|
|
|
|
NAME
|
|
----
|
|
git-read-tree - Reads tree information into the directory cache
|
|
|
|
|
|
SYNOPSIS
|
|
--------
|
|
'git-read-tree' (<tree-ish> | -m <tree-ish1> [<tree-ish2> <tree-ish3>])"
|
|
|
|
DESCRIPTION
|
|
-----------
|
|
Reads the tree information given by <tree> into the directory cache,
|
|
but does not actually _update_ any of the files it "caches". (see:
|
|
git-checkout-cache)
|
|
|
|
Optionally, it can merge a tree into the cache or perform a 3-way
|
|
merge.
|
|
|
|
Trivial merges are done by "git-read-tree" itself. Only conflicting paths
|
|
will be in unmerged state when "git-read-tree" returns.
|
|
|
|
OPTIONS
|
|
-------
|
|
-m::
|
|
Perform a merge, not just a read
|
|
|
|
<tree-ish#>::
|
|
The id of the tree object(s) to be read/merged.
|
|
|
|
|
|
Merging
|
|
-------
|
|
If '-m' is specified, "git-read-tree" performs 2 kinds of merge, a single tree
|
|
merge if only 1 tree is given or a 3-way merge if 3 trees are
|
|
provided.
|
|
|
|
Single Tree Merge
|
|
~~~~~~~~~~~~~~~~~
|
|
If only 1 tree is specified, git-read-tree operates as if the user did not
|
|
specify '-m', except that if the original cache has an entry for a
|
|
given pathname; and the contents of the path matches with the tree
|
|
being read, the stat info from the cache is used. (In other words, the
|
|
cache's stat()s take precedence over the merged tree's)
|
|
|
|
That means that if you do a "git-read-tree -m <newtree>" followed by a
|
|
"git-checkout-cache -f -a", the "git-checkout-cache" only checks out
|
|
the stuff that really changed.
|
|
|
|
This is used to avoid unnecessary false hits when "git-diff-files" is
|
|
run after git-read-tree.
|
|
|
|
3-Way Merge
|
|
~~~~~~~~~~~
|
|
Each "index" entry has two bits worth of "stage" state. stage 0 is the
|
|
normal one, and is the only one you'd see in any kind of normal use.
|
|
|
|
However, when you do "git-read-tree" with three trees, the "stage"
|
|
starts out at 1.
|
|
|
|
This means that you can do
|
|
|
|
git-read-tree -m <tree1> <tree2> <tree3>
|
|
|
|
and you will end up with an index with all of the <tree1> entries in
|
|
"stage1", all of the <tree2> entries in "stage2" and all of the
|
|
<tree3> entries in "stage3".
|
|
|
|
Furthermore, "git-read-tree" has special-case logic that says: if you see
|
|
a file that matches in all respects in the following states, it
|
|
"collapses" back to "stage0":
|
|
|
|
- stage 2 and 3 are the same; take one or the other (it makes no
|
|
difference - the same work has been done on stage 2 and 3)
|
|
|
|
- stage 1 and stage 2 are the same and stage 3 is different; take
|
|
stage 3 (some work has been done on stage 3)
|
|
|
|
- stage 1 and stage 3 are the same and stage 2 is different take
|
|
stage 2 (some work has been done on stage 2)
|
|
|
|
The "git-write-tree" command refuses to write a nonsensical tree, and it
|
|
will complain about unmerged entries if it sees a single entry that is not
|
|
stage 0.
|
|
|
|
Ok, this all sounds like a collection of totally nonsensical rules,
|
|
but it's actually exactly what you want in order to do a fast
|
|
merge. The different stages represent the "result tree" (stage 0, aka
|
|
"merged"), the original tree (stage 1, aka "orig"), and the two trees
|
|
you are trying to merge (stage 2 and 3 respectively).
|
|
|
|
In fact, the way "git-read-tree" works, it's entirely agnostic about how
|
|
you assign the stages, and you could really assign them any which way,
|
|
and the above is just a suggested way to do it (except since
|
|
"git-write-tree" refuses to write anything but stage0 entries, it makes
|
|
sense to always consider stage 0 to be the "full merge" state).
|
|
|
|
So what happens? Try it out. Select the original tree, and two trees
|
|
to merge, and look how it works:
|
|
|
|
- if a file exists in identical format in all three trees, it will
|
|
automatically collapse to "merged" state by the new git-read-tree.
|
|
|
|
- a file that has _any_ difference what-so-ever in the three trees
|
|
will stay as separate entries in the index. It's up to "script
|
|
policy" to determine how to remove the non-0 stages, and insert a
|
|
merged version. But since the index is always sorted, they're easy
|
|
to find: they'll be clustered together.
|
|
|
|
- the index file saves and restores with all this information, so you
|
|
can merge things incrementally, but as long as it has entries in
|
|
stages 1/2/3 (ie "unmerged entries") you can't write the result. So
|
|
now the merge algorithm ends up being really simple:
|
|
|
|
* you walk the index in order, and ignore all entries of stage 0,
|
|
since they've already been done.
|
|
|
|
* if you find a "stage1", but no matching "stage2" or "stage3", you
|
|
know it's been removed from both trees (it only existed in the
|
|
original tree), and you remove that entry.
|
|
|
|
* if you find a matching "stage2" and "stage3" tree, you remove one
|
|
of them, and turn the other into a "stage0" entry. Remove any
|
|
matching "stage1" entry if it exists too. .. all the normal
|
|
trivial rules ..
|
|
|
|
Incidentally - it also means that you don't even have to have a
|
|
separate subdirectory for this. All the information literally is in
|
|
the index file, which is a temporary thing anyway. There is no need to
|
|
worry about what is in the working directory, since it is never shown
|
|
and never used.
|
|
|
|
see also: link:git-write-tree.html[git-write-tree], link:git-ls-files.html[git-ls-files]
|
|
|
|
|
|
Author
|
|
------
|
|
Written by Linus Torvalds <torvalds@osdl.org>
|
|
|
|
Documentation
|
|
--------------
|
|
Documentation by David Greaves, Junio C Hamano and the git-list <git@vger.kernel.org>.
|
|
|
|
GIT
|
|
---
|
|
Part of the link:git.html[git] suite
|
|
|