[PATCH] New git-apply test cases for patches with mulitple fragments.

[git.git] / Documentation / git-read-tree.txt

diff --git a/Documentation/git-read-tree.txt b/Documentation/git-read-tree.txt
index cbde13d..e1be6cc 100644 (file)
--- a/Documentation/git-read-tree.txt
+++ b/Documentation/git-read-tree.txt
@@ -9,16 +9,19 @@ git-read-tree - Reads tree information into the directory cache
 
 SYNOPSIS
 --------
 
 SYNOPSIS
 --------

-'git-read-tree' (<tree-ish> | -m <tree-ish1> [<tree-ish2> <tree-ish3>])"
+'git-read-tree' (<tree-ish> | [-m [-u]] <tree-ish1> [<tree-ish2> [<tree-ish3>]])
+

 
 DESCRIPTION
 -----------
 
 DESCRIPTION
 -----------

-Reads the tree information given by <tree> into the directory cache,
+Reads the tree information given by <tree-ish> into the directory cache,

 but does not actually *update* any of the files it "caches". (see:
 git-checkout-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.
+Optionally, it can merge a tree into the cache, 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.
 
 Trivial merges are done by "git-read-tree" itself.  Only conflicting paths
 will be in unmerged state when "git-read-tree" returns.


@@ -26,7 +29,11 @@ will be in unmerged state when "git-read-tree" returns.
 OPTIONS
 -------
 -m::
 OPTIONS
 -------
 -m::

-       Perform a merge, not just a read
+       Perform a merge, not just a read.
+
+-u::
+       After a successful merge, update the files in the work
+       tree with the result of the merge.

 
 <tree-ish#>::
        The id of the tree object(s) to be read/merged.
 
 <tree-ish#>::
        The id of the tree object(s) to be read/merged.


@@ -34,25 +41,101 @@ OPTIONS
 
 Merging
 -------
 
 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
+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.
 
 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
 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
+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
 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)
+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
 
 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
+"git-checkout-cache -f -u -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.
 
 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 cache
+      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 cache
+     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 cache 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-cache --cached $M".  Note that this does not
+necessarily match "git-diff-cache --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-cache
+--cached $H" would have told you about the change before this
+merge, but it would not show in "git-diff-cache --cached $M"
+output after two-tree merge.
+
+

 3-Way Merge
 ~~~~~~~~~~~
 Each "index" entry has two bits worth of "stage" state. stage 0 is the
 3-Way Merge
 ~~~~~~~~~~~
 Each "index" entry has two bits worth of "stage" state. stage 0 is the


@@ -92,23 +175,18 @@ 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).
 
 "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:
+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
 
 - if a file exists in identical format in all three trees, it will

-  automatically collapse to "merged" state by the new 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
 
 - 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
+  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
   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.
+  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
 
 - the index file saves and restores with all this information, so you
   can merge things incrementally, but as long as it has entries in


@@ -127,11 +205,49 @@ to merge, and look how it works:
     matching "stage1" entry if it exists too.  .. all the normal
     trivial rules ..
 
     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.
+You would normally use "git-merge-cache" with supplied
+"git-merge-one-file-script" to do this last step.  The script
+does not touch the files in the work tree, and the entire merge
+happens in the index file.  In other words, there is no need to
+worry about what is in the working directory, since it is never
+shown and never used.
+
+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.  To illustrate, suppose you start from what has been
+commited last to your repository:
+
+    $ JC=`cat .git/HEAD`
+    $ git-checkout-cache -f -u -a $JC
+
+You do random edits, without running git-update-cache.  And then
+you notice that the tip of your "upstream" tree has advanced
+since you pulled from him:
+
+    $ git-fetch-script rsync://.... linus
+    $ LT=`cat .git/MERGE_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 cache 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-cache git-merge-one-file-script -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.
+

 
 See Also
 --------
 
 See Also
 --------