You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
364 lines
14 KiB
364 lines
14 KiB
git-read-tree(1) |
|
================ |
|
|
|
NAME |
|
---- |
|
git-read-tree - Reads tree information into the index |
|
|
|
|
|
SYNOPSIS |
|
-------- |
|
'git-read-tree' (<tree-ish> | [[-m [--trivial] [--aggressive] | --reset | --prefix=<prefix>] [-u | -i]] [--exclude-per-directory=<gitignore>] [--index-output=<file>] <tree-ish1> [<tree-ish2> [<tree-ish3>]]) |
|
|
|
|
|
DESCRIPTION |
|
----------- |
|
Reads the tree information given by <tree-ish> into the index, |
|
but does not actually *update* any of the files it "caches". (see: |
|
linkgit:git-checkout-index[1]) |
|
|
|
Optionally, it can merge a tree into the index, perform a |
|
fast-forward (i.e. 2-way) merge, or a 3-way merge, with the `-m` |
|
flag. When used with `-m`, the `-u` flag causes it to also update |
|
the files in the work tree with the result of the 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. The command will |
|
refuse to run if your index file has unmerged entries, |
|
indicating that you have not finished previous merge you |
|
started. |
|
|
|
--reset:: |
|
Same as -m, except that unmerged entries are discarded |
|
instead of failing. |
|
|
|
-u:: |
|
After a successful merge, update the files in the work |
|
tree with the result of the merge. |
|
|
|
-i:: |
|
Usually a merge requires the index file as well as the |
|
files in the working tree are up to date with the |
|
current head commit, in order not to lose local |
|
changes. This flag disables the check with the working |
|
tree and is meant to be used when creating a merge of |
|
trees that are not directly related to the current |
|
working tree status into a temporary index file. |
|
|
|
--trivial:: |
|
Restrict three-way merge by `git-read-tree` to happen |
|
only if there is no file-level merging required, instead |
|
of resolving merge for trivial cases and leaving |
|
conflicting files unresolved in the index. |
|
|
|
--aggressive:: |
|
Usually a three-way merge by `git-read-tree` resolves |
|
the merge for really trivial cases and leaves other |
|
cases unresolved in the index, so that Porcelains can |
|
implement different merge policies. This flag makes the |
|
command to resolve a few more cases internally: |
|
+ |
|
* when one side removes a path and the other side leaves the path |
|
unmodified. The resolution is to remove that path. |
|
* when both sides remove a path. The resolution is to remove that path. |
|
* when both sides adds a path identically. The resolution |
|
is to add that path. |
|
|
|
--prefix=<prefix>/:: |
|
Keep the current index contents, and read the contents |
|
of named tree-ish under directory at `<prefix>`. The |
|
original index file cannot have anything at the path |
|
`<prefix>` itself, and have nothing in `<prefix>/` |
|
directory. Note that the `<prefix>/` value must end |
|
with a slash. |
|
|
|
--exclude-per-directory=<gitignore>:: |
|
When running the command with `-u` and `-m` options, the |
|
merge result may need to overwrite paths that are not |
|
tracked in the current branch. The command usually |
|
refuses to proceed with the merge to avoid losing such a |
|
path. However this safety valve sometimes gets in the |
|
way. For example, it often happens that the other |
|
branch added a file that used to be a generated file in |
|
your branch, and the safety valve triggers when you try |
|
to switch to that branch after you ran `make` but before |
|
running `make clean` to remove the generated file. This |
|
option tells the command to read per-directory exclude |
|
file (usually '.gitignore') and allows such an untracked |
|
but explicitly ignored file to be overwritten. |
|
|
|
--index-output=<file>:: |
|
Instead of writing the results out to `$GIT_INDEX_FILE`, |
|
write the resulting index in the named file. While the |
|
command is operating, the original index file is locked |
|
with the same mechanism as usual. The file must allow |
|
to be rename(2)ed into from a temporary file that is |
|
created next to the usual index file; typically this |
|
means it needs to be on the same filesystem as the index |
|
file itself, and you need write permission to the |
|
directories the index file and index output file are |
|
located in. |
|
|
|
<tree-ish#>:: |
|
The id of the tree object(s) to be read/merged. |
|
|
|
|
|
Merging |
|
------- |
|
If `-m` is specified, `git-read-tree` can perform 3 kinds of |
|
merge, a single tree merge if only 1 tree is given, a |
|
fast-forward merge with 2 trees, 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 index has an entry for a |
|
given pathname, and the contents of the path matches with the tree |
|
being read, the stat info from the index is used. (In other words, the |
|
index'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-index -f -u -a`, the `git-checkout-index` 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`. |
|
|
|
|
|
Two Tree Merge |
|
~~~~~~~~~~~~~~ |
|
|
|
Typically, this is invoked as `git-read-tree -m $H $M`, where $H |
|
is the head commit of the current repository, and $M is the head |
|
of a foreign tree, which is simply ahead of $H (i.e. we are in a |
|
fast forward situation). |
|
|
|
When two trees are specified, the user is telling git-read-tree |
|
the following: |
|
|
|
1. The current index and work tree is derived from $H, but |
|
the user may have local changes in them since $H; |
|
|
|
2. The user wants to fast-forward to $M. |
|
|
|
In this case, the `git-read-tree -m $H $M` command makes sure |
|
that no local change is lost as the result of this "merge". |
|
Here are the "carry forward" rules: |
|
|
|
I (index) H M Result |
|
------------------------------------------------------- |
|
0 nothing nothing nothing (does not happen) |
|
1 nothing nothing exists use M |
|
2 nothing exists nothing remove path from index |
|
3 nothing exists exists use M |
|
|
|
clean I==H I==M |
|
------------------ |
|
4 yes N/A N/A nothing nothing keep index |
|
5 no N/A N/A nothing nothing keep index |
|
|
|
6 yes N/A yes nothing exists keep index |
|
7 no N/A yes nothing exists keep index |
|
8 yes N/A no nothing exists fail |
|
9 no N/A no nothing exists fail |
|
|
|
10 yes yes N/A exists nothing remove path from index |
|
11 no yes N/A exists nothing fail |
|
12 yes no N/A exists nothing fail |
|
13 no no N/A exists nothing fail |
|
|
|
clean (H=M) |
|
------ |
|
14 yes exists exists keep index |
|
15 no exists exists keep index |
|
|
|
clean I==H I==M (H!=M) |
|
------------------ |
|
16 yes no no exists exists fail |
|
17 no no no exists exists fail |
|
18 yes no yes exists exists keep index |
|
19 no no yes exists exists keep index |
|
20 yes yes no exists exists use M |
|
21 no yes no exists exists fail |
|
|
|
In all "keep index" cases, the index entry stays as in the |
|
original index file. If the entry were not up to date, |
|
git-read-tree keeps the copy in the work tree intact when |
|
operating under the -u flag. |
|
|
|
When this form of git-read-tree returns successfully, you can |
|
see what "local changes" you made are carried forward by running |
|
`git-diff-index --cached $M`. Note that this does not |
|
necessarily match `git-diff-index --cached $H` would have |
|
produced before such a two tree merge. This is because of cases |
|
18 and 19 --- if you already had the changes in $M (e.g. maybe |
|
you picked it up via e-mail in a patch form), `git-diff-index |
|
--cached $H` would have told you about the change before this |
|
merge, but it would not show in `git-diff-index --cached $M` |
|
output after two-tree merge. |
|
|
|
|
|
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". When performing a merge of another |
|
branch into the current branch, we use the common ancestor tree |
|
as <tree1>, the current branch head as <tree2>, and the other |
|
branch head as <tree3>. |
|
|
|
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 our branch in |
|
stage 2 and their branch in stage 3) |
|
|
|
- stage 1 and stage 2 are the same and stage 3 is different; take |
|
stage 3 (our branch in stage 2 did not do anything since the |
|
ancestor in stage 1 while their branch in stage 3 worked on |
|
it) |
|
|
|
- stage 1 and stage 3 are the same and stage 2 is different take |
|
stage 2 (we did something while they did nothing) |
|
|
|
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). |
|
|
|
The order of stages 1, 2 and 3 (hence the order of three |
|
<tree-ish> command line arguments) are significant when you |
|
start a 3-way merge with an index file that is already |
|
populated. Here is an outline of how the algorithm works: |
|
|
|
- if a file exists in identical format in all three trees, it will |
|
automatically collapse to "merged" state by 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 "porcelain |
|
policy" to determine how to remove the non-0 stages, and insert a |
|
merged version. |
|
|
|
- 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 (i.e., "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 .. |
|
|
|
You would normally use `git-merge-index` with supplied |
|
`git-merge-one-file` to do this last step. The script updates |
|
the files in the working tree as it merges each path and at the |
|
end of a successful merge. |
|
|
|
When you start a 3-way merge with an index file that is already |
|
populated, it is assumed that it represents the state of the |
|
files in your work tree, and you can even have files with |
|
changes unrecorded in the index file. It is further assumed |
|
that this state is "derived" from the stage 2 tree. The 3-way |
|
merge refuses to run if it finds an entry in the original index |
|
file that does not match stage 2. |
|
|
|
This is done to prevent you from losing your work-in-progress |
|
changes, and mixing your random changes in an unrelated merge |
|
commit. To illustrate, suppose you start from what has been |
|
committed last to your repository: |
|
|
|
---------------- |
|
$ JC=`git-rev-parse --verify "HEAD^0"` |
|
$ git-checkout-index -f -u -a $JC |
|
---------------- |
|
|
|
You do random edits, without running git-update-index. And then |
|
you notice that the tip of your "upstream" tree has advanced |
|
since you pulled from him: |
|
|
|
---------------- |
|
$ git-fetch git://.... linus |
|
$ LT=`cat .git/FETCH_HEAD` |
|
---------------- |
|
|
|
Your work tree is still based on your HEAD ($JC), but you have |
|
some edits since. Three-way merge makes sure that you have not |
|
added or modified index entries since $JC, and if you haven't, |
|
then does the right thing. So with the following sequence: |
|
|
|
---------------- |
|
$ git-read-tree -m -u `git-merge-base $JC $LT` $JC $LT |
|
$ git-merge-index git-merge-one-file -a |
|
$ echo "Merge with Linus" | \ |
|
git-commit-tree `git-write-tree` -p $JC -p $LT |
|
---------------- |
|
|
|
what you would commit is a pure merge between $JC and $LT without |
|
your work-in-progress changes, and your work tree would be |
|
updated to the result of the merge. |
|
|
|
However, if you have local changes in the working tree that |
|
would be overwritten by this merge,`git-read-tree` will refuse |
|
to run to prevent your changes from being lost. |
|
|
|
In other words, there is no need to worry about what exists only |
|
in the working tree. When you have local changes in a part of |
|
the project that is not involved in the merge, your changes do |
|
not interfere with the merge, and are kept intact. When they |
|
*do* interfere, the merge does not even start (`git-read-tree` |
|
complains loudly and fails without modifying anything). In such |
|
a case, you can simply continue doing what you were in the |
|
middle of doing, and when your working tree is ready (i.e. you |
|
have finished your work-in-progress), attempt the merge again. |
|
|
|
|
|
SEE ALSO |
|
-------- |
|
linkgit:git-write-tree[1]; linkgit:git-ls-files[1]; |
|
linkgit:gitignore[5] |
|
|
|
|
|
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 linkgit:git[7] suite
|
|
|