Feature request: be able to pass arguments to difftool command

Feature request: be able to pass arguments to difftool command

[H.Merijn Brand]

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In short, I want to be able to do

 $ git difftool 5c5a -v2

where -v2 is passed to the tool invoked in the end. I'll elaborate on
why ...

Background.

Some changes are not obvious to spot. One of the best examples I found
is this one:
https://github.com/hexchat/hexchat/commit/5c5aacd9da7d45dfc1644b87de9e2379a1102d6a

$ git show 5c5a
commit 5c5aacd9da7d45dfc1644b87de9e2379a1102d6a
Author: Patrick Griffis <tingping@tingping.se>
Date:   Wed Apr 4 19:21:53 2018 -0400

    Fix another bad translation

diff --git a/po/el.po b/po/el.po
index 7d47ee1e..e54d62c1 100644
--- a/po/el.po
+++ b/po/el.po
@@ -1072,7 +1072,7 @@ msgstr "%C22*%O$t%C22$1%O: %C18$2%O κατά συνέχεια %C24$4%O από %C

 #: src/common/textevents.h:13
 msgid "%C22*%O$tCannot join %C22$1 %O(%C20You are banned%O)."
-msgstr "%C22*%O$tΑδυναμία εισαγωγής %C22$1 %O(%C20Είστε μπλοκαρισμένος%Ο)."
+msgstr "%C22*%O$tΑδυναμία εισαγωγής %C22$1 %O(%C20Είστε μπλοκαρισμένος%O)."

 #: src/common/textevents.h:19
 msgid "%C29*%O$tCapabilities acknowledged: %C29$2%O"


I bet none of you is able to spot the change in that line, even if
colored. I had a similar problem completely unrelated to git, and I
wrote the "ccdiff" tool, to do horizontally colored diff. As mail (when
used without HTML, as it ought to be used) is not apt to coloring, I
added an option to show markers under the changed text. I then
integrated the tool as much as possible into git

 $ cpan App::ccdiff
 $ git config --global diff.tool ccdiff
 $ git config --global difftool.prompt false
 $ git config --global difftool.ccdiff.cmd 'ccdiff --utf-8 -u $LOCAL $REMOTE'
 $ git difftool 5c5a~..5c5a
 --- /tmp/CXbTje_el.po   Tue Aug 28 17:38:02 2018
 +++ /tmp/8jrR7d_el.po   Tue Aug 28 17:38:02 2018
 1075,1075c1075,1075

  #: src/common/textevents.h:13
  msgid "%C22*%O$tCannot join %C22$1 %O(%C20You are banned%O)."
 -msgstr "%C22*%O$tΑδυναμία εισαγωγής %C22$1 %O(%C20Είστε μπλοκαρισμένος%Ο)."
 +msgstr "%C22*%O$tΑδυναμία εισαγωγής %C22$1 %O(%C20Είστε μπλοκαρισμένος%O)."

  #: src/common/textevents.h:19
  msgid "%C29*%O$tCapabilities acknowledged: %C29$2%O"

 $ cat >~/bin/git-ccdiff <<EOC
 #!/bin/sh

 commit=$1
 shift
 if [ "$commit" = "" ]; then
     git difftool
 else
     git difftool $commit~1..$commit
     fi
 EOF
 $ chmod 755 ~/bin/git-ccdiff
 $ git ccdiff 5c5a
 --- /tmp/Cw7VDo_el.po   Tue Aug 28 17:41:08 2018
 +++ /tmp/yuTGro_el.po   Tue Aug 28 17:41:08 2018
 1075,1075c1075,1075

  #: src/common/textevents.h:13
  msgid "%C22*%O$tCannot join %C22$1 %O(%C20You are banned%O)."
 -msgstr "%C22*%O$tΑδυναμία εισαγωγής %C22$1 %O(%C20Είστε μπλοκαρισμένος%Ο)."
 +msgstr "%C22*%O$tΑδυναμία εισαγωγής %C22$1 %O(%C20Είστε μπλοκαρισμένος%O)."

  #: src/common/textevents.h:19
  msgid "%C29*%O$tCapabilities acknowledged: %C29$2%O"

So, with all parts in place, I want more info

 $ git ccdiff 5c5a -m

No change. When I add -m to the cmd in ~/.gitconfig, like

[difftool "ccdiff"]
	cmd = ccdiff --utf-8 -u -m $LOCAL $REMOTE

 $ git ccdiff 5c5a
 --- /tmp/fXkf4E_el.po   Tue Aug 28 17:44:12 2018
 +++ /tmp/P3mZ1E_el.po   Tue Aug 28 17:44:12 2018
 1075,1075c1075,1075

  #: src/common/textevents.h:13
  msgid "%C22*%O$tCannot join %C22$1 %O(%C20You are banned%O)."
 -msgstr "%C22*%O$tΑδυναμία εισαγωγής %C22$1 %O(%C20Είστε μπλοκαρισμένος%Ο)."
 -                                                                       ▼
 +msgstr "%C22*%O$tΑδυναμία εισαγωγής %C22$1 %O(%C20Είστε μπλοκαρισμένος%O)."
 +                                                                       ▲

  #: src/common/textevents.h:19
  msgid "%C29*%O$tCapabilities acknowledged: %C29$2%O"

Nice, but I still cannot pass it from the command line, and in this
specific case I also want -v2 or -v3

cmd = ccdiff --utf-8 -u -m -v2 $LOCAL $REMOTE:

--- /tmp/dp0E5T_el.po   Tue Aug 28 17:45:51 2018
+++ /tmp/za7m3T_el.po   Tue Aug 28 17:45:51 2018
1075,1075c1075,1075

  #: src/common/textevents.h:13
  msgid "%C22*%O$tCannot join %C22$1 %O(%C20You are banned%O)."
 -msgstr "%C22*%O$tΑδυναμία εισαγωγής %C22$1 %O(%C20Είστε μπλοκαρισμένος%↱Ο↰)."
 -                                                                        ▼
 - -- verbose : GREEK CAPITAL LETTER OMICRON
 +msgstr "%C22*%O$tΑδυναμία εισαγωγής %C22$1 %O(%C20Είστε μπλοκαρισμένος%↱O↰)."
 +                                                                        ▲
 + -- verbose : LATIN CAPITAL LETTER O

  #: src/common/textevents.h:19
  msgid "%C29*%O$tCapabilities acknowledged: %C29$2%O"

cmd = ccdiff --utf-8 -u -m -v3 $LOCAL $REMOTE
(a screenshot is added to show the colors)

--- /tmp/4gPKTd_el.po   Tue Aug 28 17:47:57 2018
+++ /tmp/IreaTe_el.po   Tue Aug 28 17:47:57 2018
1075,1075c1075,1075

  #: src/common/textevents.h:13
  msgid "%C22*%O$tCannot join %C22$1 %O(%C20You are banned%O)."
 -msgstr "%C22*%O$tΑδυναμία εισαγωγής %C22$1 %O(%C20Είστε μπλοκαρισμένος%↱Ο↰)."
 -                                                                        ▼
 - -- verbose : GREEK CAPITAL LETTER OMICRON (U+00039F)
 +msgstr "%C22*%O$tΑδυναμία εισαγωγής %C22$1 %O(%C20Είστε μπλοκαρισμένος%↱O↰)."
 +                                                                        ▲
 + -- verbose : LATIN CAPITAL LETTER O (U+00004F)

  #: src/common/textevents.h:19
  msgid "%C29*%O$tCapabilities acknowledged: %C29$2%O"


The only workaround I could come up with (for now) is both ugly and
fragile: I keep the extra arguments in an environment variable and add
those back to the commandline after the command started. Very easy to
break though.

$ cat ~/bin/git-ccdiff
#!/pro/bin/perl

use 5.18.3;
use warnings;

my $commit;

if (@ARGV) {
    $ARGV[0] =~ m/^-/ or $commit = shift;
    }

@ARGV and $ENV{CCDIFF_OPTIONS} = "@ARGV";
my @git = qw( git difftool );
defined $commit and push @git, "$commit~1..$commit";
system @git;


So, my wish would be to have an option, possibly using -- to pass
additional command line arguments to git difftool, so that

 $ git difftool $commit~1..$commit -- -m -v2

would pass the arguments after -- transparantly to ccdiff (in my case)


-- 
H.Merijn Brand  http://tux.nl   Perl Monger  http://amsterdam.pm.org/
using perl5.00307 .. 5.29   porting perl5 on HP-UX, AIX, and openSUSE
http://mirrors.develooper.com/hpux/        http://www.test-smoke.org/
http://qa.perl.org   http://www.goldmark.org/jeff/stupid-disclaimers/

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Re: Feature request: be able to pass arguments to difftool command

[Junio C Hamano]

"H.Merijn Brand" <h.m.brand@xs4all.nl> writes:

> So, my wish would be to have an option, possibly using -- to pass
> additional command line arguments to git difftool, so that
>
>  $ git difftool $commit~1..$commit -- -m -v2
>
> would pass the arguments after -- transparantly to ccdiff (in my case)

At the syntax level passing any option after "--" would be a no
starter, as I would imagine that "git difftool $revs -- $paths"
should still be supported.

At the concept level, however, I can see why such a feature would be
useful.  Perhaps

    $ git difftool --backend-option=-m --backend-option=-v2 HEAD
    $ git mergetool --backend-option=--foo

with appropriate way(s) [*1*] to make it easier to type (and
implement) would be an acceptable avenue to pursue, I wonder?


[Footnote]

*1* There are various possible ways, not all of them are mutually
    incompatible.

    a. Give a short-form synonym, e.g. -X, to "--backend-option";

    b. Assume that backend option always begins with a dash and add
       one when missing, e.g. -Xm becomes --backend-option=-m

    c. Allow giving multiple backend options on a single option and
       split at whitespace, e.g. --backend-option="-m -v2"

    d. Allow difftool.$toolname.opts configuration variable that is
       multi-valued, so you can say

	git -c difftool.ccdiff.opts=-v2 -c difftool.ccdiff.opts=-m difftool

       (of course, not necessarily from the command line but the
       point is you could configure it)

    Some of these (e.g. b, c) may not be desirable, though.

Re: Feature request: be able to pass arguments to difftool command

[H.Merijn Brand]

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On Tue, 28 Aug 2018 12:37:40 -0700, Junio C Hamano <gitster@pobox.com>
wrote:

> "H.Merijn Brand" <h.m.brand@xs4all.nl> writes:
> 
> > So, my wish would be to have an option, possibly using -- to pass
> > additional command line arguments to git difftool, so that
> >
> >  $ git difftool $commit~1..$commit -- -m -v2
> >
> > would pass the arguments after -- transparantly to ccdiff (in my case)  
> 
> At the syntax level passing any option after "--" would be a no
> starter, as I would imagine that "git difftool $revs -- $paths"
> should still be supported.
> 
> At the concept level, however, I can see why such a feature would be
> useful.  Perhaps
> 
>     $ git difftool --backend-option=-m --backend-option=-v2 HEAD
>     $ git mergetool --backend-option=--foo

This would mean I can just pass remaining arguments, like this?

--8<--- ~/bin/git-ccdiff
#!/usr/bin/env perl
use 5.18.3;
use warnings;

my $commit;

@ARGV && $ARGV[0] !~ m/^-/ and $commit = shift;

my @git = qw( git difftool );
defined $commit and push @git, "$commit~1..$commit";
system @git, @ARGV;
-->8---

> with appropriate way(s) [*1*] to make it easier to type (and
> implement) would be an acceptable avenue to pursue, I wonder?

I like it, as long as they are all separate options in the backend and
not available in one single variable that needs to be split

I can envision a configure variable like

  backends.options.separator = U+2063

so the backend can safely split on that itself. But I also see this as
overly complex en over-engineering

> [Footnote]
> 
> *1* There are various possible ways, not all of them are mutually
>     incompatible.
> 
>     a. Give a short-form synonym, e.g. -X, to "--backend-option";

I like it

>     b. Assume that backend option always begins with a dash and add
>        one when missing, e.g. -Xm becomes --backend-option=-m

I guess not: there might be tools that do not work like that, e.g.
xfreerdp changed all their rememberable and logic options to the weird
stupid syntax they use now, including mixing -, -- and +

 rdesktop -u user -p - -g 1280x1024 -a 16 -r clipboard:CLIPBOARD host

->

 xfreerdp -u user --from-stdin -g 1280x1024 -a 16 --plugin clipbrd host

->

 xfreerdp /u:user /from-stdin /size:1280x1024 /bpp:16 +clipboard /v:host

>     c. Allow giving multiple backend options on a single option and
>        split at whitespace, e.g. --backend-option="-m -v2"

That is the weak part in my workaround, as it will break on options like

  --backend-option='--config="/path/to/My Configuration/My Application"'

>     d. Allow difftool.$toolname.opts configuration variable that is
>        multi-valued, so you can say
> 
> 	git -c difftool.ccdiff.opts=-v2 -c difftool.ccdiff.opts=-m difftool

Hmm, maybe harder to explain, but why not

>        (of course, not necessarily from the command line but the
>        point is you could configure it)
> 
>     Some of these (e.g. b, c) may not be desirable, though.


-- 
H.Merijn Brand  http://tux.nl   Perl Monger  http://amsterdam.pm.org/
using perl5.00307 .. 5.29   porting perl5 on HP-UX, AIX, and openSUSE
http://mirrors.develooper.com/hpux/        http://www.test-smoke.org/
http://qa.perl.org   http://www.goldmark.org/jeff/stupid-disclaimers/

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Re: Feature request: be able to pass arguments to difftool command

[David Aguilar]

On Wed, Aug 29, 2018 at 09:18:38AM +0200, H.Merijn Brand wrote:
> On Tue, 28 Aug 2018 12:37:40 -0700, Junio C Hamano <gitster@pobox.com>
> wrote:
> 
> > "H.Merijn Brand" <h.m.brand@xs4all.nl> writes:
> > 
> > > So, my wish would be to have an option, possibly using -- to pass
> > > additional command line arguments to git difftool, so that
> > >
> > >  $ git difftool $commit~1..$commit -- -m -v2
> > >
> > > would pass the arguments after -- transparantly to ccdiff (in my case)  
> > 
> > At the syntax level passing any option after "--" would be a no
> > starter, as I would imagine that "git difftool $revs -- $paths"
> > should still be supported.
> > 
> > At the concept level, however, I can see why such a feature would be
> > useful.  Perhaps
> > 
> >     $ git difftool --backend-option=-m --backend-option=-v2 HEAD
> >     $ git mergetool --backend-option=--foo
> 
> This would mean I can just pass remaining arguments, like this?
> 
> --8<--- ~/bin/git-ccdiff
> #!/usr/bin/env perl
> use 5.18.3;
> use warnings;
> 
> my $commit;
> 
> @ARGV && $ARGV[0] !~ m/^-/ and $commit = shift;
> 
> my @git = qw( git difftool );
> defined $commit and push @git, "$commit~1..$commit";
> system @git, @ARGV;
> -->8---
> 
> > with appropriate way(s) [*1*] to make it easier to type (and
> > implement) would be an acceptable avenue to pursue, I wonder?
> 
> I like it, as long as they are all separate options in the backend and
> not available in one single variable that needs to be split
> 
> I can envision a configure variable like
> 
>   backends.options.separator = U+2063
> 
> so the backend can safely split on that itself. But I also see this as
> overly complex en over-engineering


Personally, I think it'd be better to keep the tool simple.

While I do see the utility, it would be just as easy to configure a 2nd
and 3rd variant of the same difftool and use those as needed instead.

"git difftool -t ccdiff2" or "-t ccdiff3" is the simplest, and there's
nothing stopping the user from creating aliases to shorten it further.

We also already have, "git difftool -x / --extcmd"
for specifying a full-on external diff command.

> 	git -c difftool.ccdiff.opts=-v2 -c difftool.ccdiff.opts=-m difftool

For example, this seems simpler as:

	git difftool -x 'ccdiff -v2 -m'

We already have two mechanisms for controlling the inner command that's
launched by difftool.  IMO we don't need more.

My primary concerns with --backend-opts are as follows:

1. If we add a mechansim for passing -X/--backend-opts, then we
   need to specify a new variable that users will need to be aware
   of when creating custom commands.  (sorry for stating the obvious)

2. All of the built-in commands would need to change to honor that
   variable.

3. The documentation becomes more complex because someone that wants
   to configure a bog-standard custom external tool now needs to
   be aware of this extra external source of arguments.

#1 and #2 are primarily implementation concerns, but #3 suggests
to me that it's over-complicating things.

Furthermore, #2 is not really that simple.
What would the sciplet look like?

	diff_cmd () {
		"$merge_tool_path" $EXTRA_ARGS ...
	}

That implies that we would need to shell quote stuff when
constructing $EXTRA_ARGS internally if we were to support multiple -X
arguments.  That just made it a bit more complex.

IMO we should be working to simpliify, not make things more complex for
rare use cases.  There's no reason the user can't just do:

	V=2 git difftool
	V=3 git difftool

... and let the inner script check for $V (or any other) variable.
While environment variables aren't great, this does seem like the right
place to use them.

Another option -- we already eval the configured command, so if the user
includes a variable ($ARGS) in their custom configuration then they can
specify extra flags today without needing to change the tool.  ex:

	[difftool "ccdiff"]
		cmd = ccdiff $ARGS \"$LOCAL\" \"$REMOTE\"

	ARGS='-v2 -m' git difftool HEAD~1..HEAD


Are these alternatives short and simple enough?
-- 
David

Re: Feature request: be able to pass arguments to difftool command

[Junio C Hamano]

David Aguilar <davvid@gmail.com> writes:

> While I do see the utility, it would be just as easy to configure a 2nd
> and 3rd variant of the same difftool and use those as needed instead.
>
> "git difftool -t ccdiff2" or "-t ccdiff3" is the simplest, and there's
> nothing stopping the user from creating aliases to shorten it further.
> ...
> We already have two mechanisms for controlling the inner command that's
> launched by difftool.  IMO we don't need more.

OK, fair enough.