~~~~~~~~~~~~~~~~~
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).
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,
+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
+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