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[PATCH] read-tree: save more user hassles during fast-forward.

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This implements the "never lose the current cache information or
the work tree state, but favor a successful merge over merge
failure" principle in the fast-forward two-tree merge operation.

It comes with a set of tests to cover all the cases described in
the case matrix found in the new documentation.

Signed-off-by: Junio C Hamano <junkio@cox.net>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Junio C Hamano
2005-06-07 11:36:30 -07:00
committed by Linus Torvalds
parent 63aff4fed9
commit c859600954
4 changed files with 698 additions and 13 deletions
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74
Documentation/git-read-tree.txt
View File

@ -53,6 +53,80 @@ 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