Re: git diff across submodules

> Junio C Hamano <gitster@pobox.com> writes:
> 
>> I also suspect that you do not have to change "git diff" at all to
>> show the patch recursively by using the attribute mechanism (look in
>> Documentation/gitattributes.text for a string GIT_EXTERNAL_DIFF).
>> It might be just as simple as doing this:
>>
>> 	echo >.gitattributes "/lib/frotz diff=subrecurse" 
>> 	git config diff.subrecurse.command $HOME/bin/diff-subrecurse
>>       cat >$HOME/bin/diff-subrecurse <<\-EOF
>> 	#!/bin/sh
>>       path=$1 old_hex=$3 new_hex=$6
>>       unset GIT_DIR
>>       cd "$path" || exit 1
>>       git diff "$old_hex" "$new_hex"        
>>       EOF
>>       chmod +x $HOME/bin/diff-subrecurse
>>
>> The corner cases like "new submodule", "removed submodule" are left
>> as an exercise to the reader ;-)
> 
> It turns out that essentially the above outline I concocted in my
> MUA is usable almost as-is.
> 
> Here is what I ended up with.
> 
>  * In .git/config of the superproject, I added this:
> 
>         [diff "submodule-recurse"]
> 		command = src/bin/diff-submodule-recurse
> 
>  * In the superproject, src/bin/diff-submodule-recurse has this
>    (this is probably whitespace damaged---the lines must be indented
>    by HT for the here document to correctly work):
> 
>         #!/bin/sh
>         # $1   $2       $3      $4       $5       $6      $7
>         # path old-file old-hex old-mode new-file new-hex new-mode
> 
>         case "$#,$4,$7" in
>         7,160000,160000) ;;
>         *)      echo "diff --git a/$1 b/$1"
>                 echo "(punt)"
>                 exit
>                 ;;
>         esac
>         unset GIT_DIR
>         cd "$1" || {
>                 cat <<-\EOF
>                 diff --git a/$1 b/$1
>                 (cannot chdir to $1)
> 		-Subproject commit $3
> 		+Subproject commit $6
>                 EOF
>         }
>         git --no-pager diff --src-prefix="s/$1/" --dst-prefix="m/$1/" "$3" "$6"
> 
>  * In .gitattributes of the superproject, I have this:
> 
>         /var	diff=submodule-recurse
> 
> The superproject in this case is a repository to control what I have
> in my $HOME directory (e.g. it has src/dot/Makefile that builds and
> installs the appropriate dotfiles, src/bin/Makefile that builds and
> installs to $HOME/bin, etc.), and one subdirectory, 'var', is a
> submodule that is only cloned to some but not all machines I clone
> this superproject to.
> 
> With this setting, things like
> 
> 	$ git diff HEAD~20
> 
> show differences with recursion into the var/ submodule just fine.