Andreas Gruenbacher [off-list ref] writes:
Can git be changed to ...
Just to save your time coming up with more ways to *change* git diff...
Even though I wouldn't say _any_ change is too late to bring in, change in
the output format from "git diff" family _must_ be usable by "git apply"
people have been using for the last 4 years or so.
Suppose your updated version of "git diff" with a certain set of options
produces output A, which is different from the output B you would get out
of today's "git diff" that is run with the same set of options.
If "git apply" people have been using understands B (i.e. current output)
and does something, the format change between A and B must be designed in
such a way that the same "git apply" accepts A (i.e. your output) and do
the same thing.
Two examples:
- "git diff -M" (or "git show -M") is _defined_ to show the filenames
without prefix on "rename from" line, and deployed "git apply" relies
on this definition to apply the patch to the file the patch was meant
to apply. If your modified "git diff -M" changes it to add the prefix,
and existing "git apply" changes behaviour (either by rejecting your
output, or applying the patch to a wrong file), then such a change has
*no chance* of getting in. It is merely a breakage.
- If you say "git diff --src-prefix=a/b/c --dst-prefix=x/y", it _might_
produce something "git apply" won't grok (I haven't checked this,
though). You can suggest to change the output from such a case to work
better. We didn't work as expected so a change _could_ be a fix.
The output from "git diff --no-index" is an exception to the above rule.
It is primarily for people who have unmanaged contents and want to use
features of the git diff engine that are not found in other people's diff
implementations (e.g. wordwise colored diff), and the header part of its
output does not currently follow "git diff" convention to be grokkable by
"git apply".
Fixing _that_ is a welcome change, but I suspect that there are corner
cases, e.g. "git diff --no-index frotz-1.2.36/ /tmp/frotz/" (i.e. you have
a pristine version in frotz-1.2.36 directory, but your modified version is
in /tmp/frtoz/) that might make fixing it fundamentally impossible (I
haven't looked into it for a long time, so it could be easy, but my gut
feeling is it isn't).
Quoting Junio C Hamano [off-list ref]
The output from "git diff --no-index" is an exception to the above rule.
It is primarily for people who have unmanaged contents and want to use
features of the git diff engine that are not found in other people's diff
implementations (e.g. wordwise colored diff),...
Is it possible to give --no-index option to "git grep", please?
--
Nanako Shiraishi
http://ivory.ap.teacup.com/nanako3/
On Thursday 14 January 2010 01:16:21 am Junio C Hamano wrote:
Andreas Gruenbacher [off-list ref] writes:
quoted
Can git be changed to ...
Just to save your time coming up with more ways to *change* git diff...
Even though I wouldn't say _any_ change is too late to bring in, change in
the output format from "git diff" family _must_ be usable by "git apply"
people have been using for the last 4 years or so.
Suppose your updated version of "git diff" with a certain set of options
produces output A, which is different from the output B you would get out
of today's "git diff" that is run with the same set of options.
If "git apply" people have been using understands B (i.e. current output)
and does something, the format change between A and B must be designed in
such a way that the same "git apply" accepts A (i.e. your output) and do
the same thing.
Two examples:
- "git diff -M" (or "git show -M") is _defined_ to show the filenames
without prefix on "rename from" line, and deployed "git apply" relies
on this definition to apply the patch to the file the patch was meant
to apply. If your modified "git diff -M" changes it to add the prefix,
and existing "git apply" changes behaviour (either by rejecting your
output, or applying the patch to a wrong file), then such a change has
*no chance* of getting in. It is merely a breakage.
Git apply is currently broken in some (uncommon) cases. Consider the
following two patches:
$ cat add.diff
diff --git a/d/f b/d/f
new file mode 100644
index 0000000..6a69f92
--- /dev/null
+++ b/d/f
@@ -0,0 +1 @@
+f
$ cat rename.diff
diff --git a/d/f b/d/g
similarity index 100%
rename from d/f
rename to d/g
They apply fine after each other with plain "git apply". When you try to
apply them to a different location, things break though:
$ git apply --directory e -p2 add.diff
$ git apply --directory e -p2 rename.diff
error: e/d/f: No such file or directory
Had the second patch not been generated with "git diff -M", things would just
have worked; in other words, the -M format is broken.
I think the easiest way to fix this in "git apply" would be to figure out what
the missing prefixes are in the rename and copy lines (in this case, just "a/"
and "b/"), and to prepend those prefixes to the decoded filenames before
stripping off pathname components. This is the same as just taking the
filenames from the "diff --git" line, and ignoring the filenames in the "copy
from", "copy to", "rename from", and "rename to" headers.
I don't see a way how to fix this in the existing headers in a backwards
compatible way. Do you?
Independent of whether and how this is addressed, can I please at least have
the "diff --git" line parsing problem fixed so that filenames which contain
spaces are put in double quotes there? Then I can at least ignore all the
prefix-less filenames in GNU patch and still make it understand git's output.
- If you say "git diff --src-prefix=a/b/c --dst-prefix=x/y", it _might_
produce something "git apply" won't grok (I haven't checked this,
though). You can suggest to change the output from such a case to work
better. We didn't work as expected so a change _could_ be a fix.
The output format for that is fine.
The output from "git diff --no-index" is an exception to the above rule.
It is primarily for people who have unmanaged contents and want to use
features of the git diff engine that are not found in other people's diff
implementations (e.g. wordwise colored diff), and the header part of its
output does not currently follow "git diff" convention to be grokkable by
"git apply".
Fixing _that_ is a welcome change, but I suspect that there are corner
cases, e.g. "git diff --no-index frotz-1.2.36/ /tmp/frotz/" (i.e. you have
a pristine version in frotz-1.2.36 directory, but your modified version is
in /tmp/frtoz/) that might make fixing it fundamentally impossible (I
haven't looked into it for a long time, so it could be easy, but my gut
feeling is it isn't).
Patches with a different number of components in the from and to prefixes are
a really bad idea. (GNU patch will prefer the pathname with the fewer
components, but this yould just as well be the wrong one.)
Thanks,
Andreas