--------
'git read-tree' [[-m [--trivial] [--aggressive] | --reset | --prefix=<prefix>]
[-u [--exclude-per-directory=<gitignore>] | -i]]
- [--index-output=<file>]
+ [--index-output=<file>] [--no-sparse-checkout]
<tree-ish1> [<tree-ish2> [<tree-ish3>]]
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.
+Trivial merges are done by 'git read-tree' itself. Only conflicting paths
+will be in unmerged state when 'git read-tree' returns.
OPTIONS
-------
Show the progress of checking files out.
--trivial::
- Restrict three-way merge by 'git-read-tree' to happen
+ 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
+ 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
directories the index file and index output file are
located in.
+--no-sparse-checkout::
+ Disable sparse checkout support even if `core.sparseCheckout`
+ is true.
+
<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
+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
+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
+given pathname, and the contents of the path match 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
+`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'.
+This is used to avoid unnecessary false hits when 'git diff-files' is
+run after 'git read-tree'.
Two Tree Merge
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'
+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;
+ 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:
+Here are the "carry forward" rules, where "I" denotes the index,
+"clean" means that index and work tree coincide, and "exists"/"nothing"
+refer to the presence of a path in the specified commit:
- I (index) H M Result
+ I 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 if "initial checkout"
+ 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 if "initial checkout",
H == M keep index otherwise
- exists fail
+ exists, fail
H != 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
+ 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
+ 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)
+ clean (H==M)
------
14 yes exists exists keep index
15 no exists exists keep index
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
+original index file. If the entry is 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
+When this form of 'git read-tree' returns successfully, you can
+see which of the "local changes" that you made were carried forward by running
`git diff-index --cached $M`. Note that this does not
-necessarily match `git diff-index --cached $H` would have
+necessarily match what `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.
+output after the two-tree merge.
-Case #3 is slightly tricky and needs explanation. The result from this
+Case 3 is slightly tricky and needs explanation. The result from this
rule logically should be to remove the path if the user staged the removal
of the path and then switching to a new branch. That however will prevent
the initial checkout from happening, so the rule is modified to use M (new
-tree) only when the contents of the index is empty. Otherwise the removal
+tree) only when the content of the index is empty. Otherwise the removal
of the path is kept as long as $H and $M are the same.
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"
+However, when you do 'git read-tree' with three trees, the "stage"
starts out at 1.
This means that you can do
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
+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 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
+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.
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'.
+ 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
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
+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.
$ git checkout-index -f -u -a $JC
----------------
-You do random edits, without running 'git-update-index'. And then
+You do random edits, without running 'git update-index'. And then
you notice that the tip of your "upstream" tree has advanced
since you pulled from him:
updated to the result of the merge.
However, if you have local changes in the working tree that
-would be overwritten by this merge, 'git-read-tree' will refuse
+would be overwritten by this merge, 'git read-tree' will refuse
to run to prevent your changes from being lost.
In other words, there is no need to worry about what exists only
in the working tree. When you have local changes in a part of
the project that is not involved in the merge, your changes do
not interfere with the merge, and are kept intact. When they
-*do* interfere, the merge does not even start ('git-read-tree'
+*do* interfere, the merge does not even start ('git read-tree'
complains loudly and fails without modifying anything). In such
a case, you can simply continue doing what you were in the
middle of doing, and when your working tree is ready (i.e. you
have finished your work-in-progress), attempt the merge again.
+Sparse checkout
+---------------
+
+"Sparse checkout" allows to sparsely populate working directory.
+It uses skip-worktree bit (see linkgit:git-update-index[1]) to tell
+Git whether a file on working directory is worth looking at.
+
+"git read-tree" and other merge-based commands ("git merge", "git
+checkout"...) can help maintaining skip-worktree bitmap and working
+directory update. `$GIT_DIR/info/sparse-checkout` is used to
+define the skip-worktree reference bitmap. When "git read-tree" needs
+to update working directory, it will reset skip-worktree bit in index
+based on this file, which uses the same syntax as .gitignore files.
+If an entry matches a pattern in this file, skip-worktree will be
+set on that entry. Otherwise, skip-worktree will be unset.
+
+Then it compares the new skip-worktree value with the previous one. If
+skip-worktree turns from unset to set, it will add the corresponding
+file back. If it turns from set to unset, that file will be removed.
+
+While `$GIT_DIR/info/sparse-checkout` is usually used to specify what
+files are in. You can also specify what files are _not_ in, using
+negate patterns. For example, to remove file "unwanted":
+
+----------------
+*
+!unwanted
+----------------
+
+Another tricky thing is fully repopulating working directory when you
+no longer want sparse checkout. You cannot just disable "sparse
+checkout" because skip-worktree are still in the index and you working
+directory is still sparsely populated. You should re-populate working
+directory with the `$GIT_DIR/info/sparse-checkout` file content as
+follows:
+
+----------------
+*
+----------------
+
+Then you can disable sparse checkout. Sparse checkout support in "git
+read-tree" and similar commands is disabled by default. You need to
+turn `core.sparseCheckout` on in order to have sparse checkout
+support.
+
+
SEE ALSO
--------
linkgit:git-write-tree[1]; linkgit:git-ls-files[1];