Fixing the p4merge launch shell script

Fixing the p4merge launch shell script

[Jeremy Morton]

Hi,

I've noticed that the p4merge shell script could do with some 
improvement when it comes to merging.  Because p4merge throws up an 
error when one of the files it's given to diff is "/dev/null", git needs 
to create a temporary empty file and pass that to p4merge when diffing a 
file that has been created/deleted (eg. create file, git add ., git diff 
--cached).

At the moment, the hack I'm using, which works, is to create a 
c:/blank.txt file which is an empty file, and modify 
"libexec/git-core/mergetools/p4merge" to start with this:

diff_cmd () {
	if [ ! -f "$LOCAL" ]
	then
		LOCAL="C:/blank.txt"
	fi
	if [ ! -f "$REMOTE" ]
	then
		REMOTE="C:/blank.txt"
	fi
	"$merge_tool_path" "$LOCAL" "$REMOTE"
}

Obviously, this isn't good enough because c:/blank.txt probably won't 
exist on the system.  It would be nice for the temporary blank file to 
have the same extension as the one that's been added, so we could diff 
(say) c:/users/jez/Temp/abc123_newFile.foo 
c:/development/bar/newfile.foo.  However, I can't see a way to do this 
purely from within the shell script (even `mktemp` doesn't exist on all 
systems so that isn't good enough).  I believe git needs to create this 
temporary blank file itself, much like it creates a temporary file for 
the previous version of a file that's been modified when it's being 
diff'd.  It then needs to expose the location of this temporary file as 
a variable; say $LOCALBLANK.  So, we would be able to modify the shell 
script to this:


diff_cmd () {
	if [ ! -f "$LOCAL" ]
	then
		LOCAL=$LOCALBLANK
	fi
	if [ ! -f "$REMOTE" ]
	then
		REMOTE=$REMOTEBLANK
	fi
	"$merge_tool_path" "$LOCAL" "$REMOTE"
}

Thoughts?  Is there an easier way to do this?

-- 
Best regards,
Jeremy Morton (Jez)

Re: Fixing the p4merge launch shell script

[Junio C Hamano]

Jeremy Morton <admin@game-point.net> writes:

> I've noticed that the p4merge shell script could do with some
> improvement when it comes to merging.  Because p4merge throws up an
> error when one of the files it's given to diff is "/dev/null", git
> needs to create a temporary empty file and pass that to p4merge when
> diffing a file that has been created/deleted (eg. create file, git add
> ., git diff --cached).
> ...
> Thoughts?  Is there an easier way to do this?

Which version of git?  Perhaps you do not have ec245ba (mergetool:
Provide an empty file when needed, 2012-01-19) yet?

Re: Fixing the p4merge launch shell script

[Jeremy Morton]

Junio C Hamano <gitster <at> pobox.com> writes:

> 
> Jeremy Morton <admin <at> game-point.net> writes:
> 
> > I've noticed that the p4merge shell script could do with some
> > improvement when it comes to merging.  Because p4merge throws up an
> > error when one of the files it's given to diff is "/dev/null", git
> > needs to create a temporary empty file and pass that to p4merge when
> > diffing a file that has been created/deleted (eg. create file, git add
> > ., git diff --cached).
> > ...
> > Thoughts?  Is there an easier way to do this?
> 
> Which version of git?  Perhaps you do not have ec245ba (mergetool:
> Provide an empty file when needed, 2012-01-19) yet?
> 

That patch fixes the mergetool part, but the part I was referring to was the
difftool part, which still has this problem.

Best regards,
Jeremy Morton (Jez)

Re: Fixing the p4merge launch shell script

[David Aguilar]

On Wed, Oct 3, 2012 at 1:34 AM, Jeremy Morton <admin@game-point.net> wrote:
> Junio C Hamano <gitster <at> pobox.com> writes:
>
>>
>> Jeremy Morton <admin <at> game-point.net> writes:
>>
>> > I've noticed that the p4merge shell script could do with some
>> > improvement when it comes to merging.  Because p4merge throws up an
>> > error when one of the files it's given to diff is "/dev/null", git
>> > needs to create a temporary empty file and pass that to p4merge when
>> > diffing a file that has been created/deleted (eg. create file, git add
>> > ., git diff --cached).
>> > ...
>> > Thoughts?  Is there an easier way to do this?
>>
>> Which version of git?  Perhaps you do not have ec245ba (mergetool:
>> Provide an empty file when needed, 2012-01-19) yet?
>>
>
> That patch fixes the mergetool part, but the part I was referring to was the
> difftool part, which still has this problem.
>
> Best regards,
> Jeremy Morton (Jez)

Thanks for the heads-up, Jez.

I should have some time to take a look this weekend.
If someone beats me to it I'll be happy to review the patches before
then (Jeremy? ;-)

Is `git diff` giving us /dev/null as the path here,
and p4merge doesn't like that, or is something else
going on?

If that's indeed happening, then I would imagine
a sensible thing for git-difftool--helper to do
would be to check for /dev/null and create some
temporary empty file.

Does that sound like the right way to go?
Another option would be for git-diff's external diff
code to handle it at a much earlier point, perhaps
guarded behind an option that git-difftool knows to
pass (changing existing behavior is off the table).

These both sound like pretty big changes given
that we're getting ready for 1.8.0.

If it's just p4merge that doesn't like this then
perhaps the right decision is to paper over it
in p4merge's mergetools/ scriptlet.

It's certainly the least-impactful option.  Thoughts?
-- 
David