Re: [RFH] "diff -B -M"

Junio C Hamano [off-list ref] writes:

5. Third twist: rewriting by copying
...
One possible way to fix this is to include another patch in the same
patchset that shows the deletion of major-11.txt.  The rule 2. would
be further revised to something like:

 rule 2. a patch renaming file A to file B requires that file A
         exists and file B does not exist in the target tree, unless
         another patch in the patchset renames file B to some other
         file (possibly but not necessarily file A) or removed file

Typofix: s/removed/removes/

         B, in which case file B must appear in the target tree.

Such a patchset would look like this:

    diff --git a/major-08.txt b/major-11.txt
    similarity index 97%
    rename from major-08.txt
    rename to major-11.txt
...
    diff --git a/major-11.txt b/major-11.txt
    deleted file mode 100644
...

And these patches, under the re-revised rule 2. and rule 4., would
apply cleanly to the old tree.

What about the reverse application?  It would be a patchset that
creates major-11.txt from nothingness, and creates major-08.txt by
renaming major-11.txt and editing.  Is the rule 2. re-revised above
sufficient?

    renaming major-11.txt to major-08.txt requires that major-08.txt
    does not exist in the target tree, unless...

and the new tree (which is the target of the reverse application)
only has major-11.txt and not major-08.txt, so this rename should go
through.  The reverse of the deletion of major-11.txt is a creation
of it with the contents fully given as the pre-image of the
(original) patch before reversing it, so that should also be OK with
rule 3.

... But rule 3. needs tweaking.  The second patch would be creating
major-11.txt which requires major-11.txt to be missing in the target
tree.  But obviously, the new tree the patch we are applying in
reverse was taken from has major-11.txt.  So we would need a
revision to it as well.

 rule 3. a patch that creates file A requires that file A does not exist
         in the target tree, unless another patch in the same patchset
         renames file A away or removes it.

So tentatively, I would say...

	Action item: do not filter delete-half of the broken pair
	out, even when the other create-half of the pair no longer
	is in the output.

	Action item: update "git apply" to honor the rule 2.
	re-revised above.

The latter should read:

	update "git apply" to honor the revised rule 2. and 3.