Re: [PATCH 2/3] Fix the processing of multiple patch files with --check in git-apply.

[Junio C Hamano <junkio@cox.net>]

Robert Fitzsimons <robfitz@273k.net> writes:

> No problem I know it's a controversial change.

Not really controversial anymore, as long as --ignore-applied is
used only when appropriate.

>>> Yes my change has a bug with a copy patch which modifies the same file.
> I'll send on a fix now.

Here is another one that the patch seems to regress.

Unfortunately this turns out to be a death sentence to the
'multiple patch touching the same file' patch.

Note that patches from a single 'git-diff-*' run are supposed to
be independent, so the second one that copy-edits from frotz to
rezrov copies frotz _before_ it is modified and then makes its
modification.

On the other hand, we can have one 'git-diff-*' run that
modifies frotz in place, and then a separate 'git-diff-*' run
that copies frotz to rezrov and then modifies rezrov, and feed
the concatenation of the two to git-apply.  That would look very
similar to a single run that edits frotz and copy-edits rezrov,
but the pre-image to create rezrov would use the post-edit image
of frotz from the first patch.  Without an explicit "here an
output from the next git-diff-*' run begins" marker, we cannot
tell these two apart.

This means that applying multiple-patches concatenated in a
single file does not make much sense.  There is no guarantee
that we can detect where the first 'git-diff-*' output ends, at
which point we need to reset the status of 'frotz' to
post-modification image of the first patch.  And if we can
detect reliably where one 'git-diff-*' output ends and the next
one begins, we could just split the input there and run
git-apply independently.  So my conclusion is to just drop this
patch, and instead tell people not to feed overlapping outputs
from multiple git-diff-* runs to a single invocation of
git-apply.

I personally do not mind considering --ignore-applied
independently from the multiple-patch-files changes, though.

------------
echo frotz >frotz
git-apply --check <<\EOF
diff --git a/frotz b/frotz
--- a/frotz
+++ b/frotz
@@ -1 +1 @@
-frotz
+frottz
diff --git a/frotz b/rezrov
similarity index 64%
copy from frotz
copy to rezrov
--- a/frotz
+++ b/rezrov
@@ -1 +1 @@
-frotz
+frotttz
EOF