patch: rewrite reversehunks (issue5337)...
patch: rewrite reversehunks (issue5337)
The old reversehunks code accesses "crecord.uihunk._hunk", which is the raw
recordhunk without crecord selection information, therefore "revert -i"
cannot revert individual lines, aka. issue5337.
The patch rewrites related logic to return the right reverse hunk for
revert. Namely,
1. "fromline" and "toline" are correctly swapped [1]
2. crecord.uihunk generates a correct reverse hunk [2]
Besides, reversehunks(hunks) will no longer modify its input "hunks", which
is more expected.
[1]: To explain why "fromline" and "toline" need to be swapped, take the
following example:
$ cat > a <<EOF
> 1
> 2
> 3
> 4
> EOF
$ cat > b <<EOF
> 2
> 3
> 5
> EOF
$ diff a b
1d0 <---- "1" is "fromline" and "0" is "toline"
< 1 and they are swapped if diff from the reversed direction
4c3 |
< 4 |
--- |
> 5 |
|
$ diff b a |
0a1 <---------+
> 1
3c4 <---- also "4c3" gets swapped to "3c4"
< 5
---
> 4
[2]: This is a bit tricky.
For example, given a file which is empty in working parent but has 3 lines
in working copy, and the user selection:
select hunk to discard
[x] +1
[ ] +2
[x] +3
The user intent is to drop "1" and "3" in working copy but keep "2", so the
reverse patch would be something like:
-1
2 (2 is a "context line")
-3
We cannot just take all selected lines and swap "-" and "+", which will be:
-1
-3
That patch won't apply because of "2". So the correct way is to insert "2"
as a "context line" by inserting it first then deleting it:
-2
+2
Therefore, the correct revert patch is:
-1
-2
+2
-3
It could be reordered to look more like a common diff hunk:
-1
-2
-3
+2
Note: It's possible to return multiple hunks so there won't be lines like
"-2", "+2". But the current implementation is much simpler.
For deletions, like the working parent has "1\n2\n3\n" and it was changed to
empty in working copy:
select hunk to discard
[x] -1
[ ] -2
[x] -3
The user intent is to drop the deletion of 1 and 3 (in other words, keep
those lines), but still delete "2".
The reverse patch is meant to be applied to working copy which is empty.
So the patch would be:
+1
+3
That is to say, there is no need to special handle the unselected "2" like
the above insertion case.