Re: [PATCH 2/2] difftool --dir-diff: symlink all files matching the working tree

> Some users like to edit files in their diff tool when using "git
> difftool --dir-diff --symlink" to compare against the working tree but
> difftool currently only created symlinks when a file contains unstaged
> changes.
>
> Change this behaviour so that symlinks are created whenever the
> right-hand side of the comparison has the same SHA1 as the file in the
> working tree.
>
> Note that textconv filters are handled in the same way as by git-diff
> and if a clean filter is not the inverse of its smudge filter we already
> get a null SHA1 from "diff --raw" and will symlink the file without
> going through the new hash-object based check.
>
> Reported-by: Matt McClure <matthewlmcclure@gmail.com>
> Signed-off-by: John Keeping <john@keeping.me.uk>
> ---
>  Documentation/git-difftool.txt |  4 +++-
>  git-difftool.perl              | 21 ++++++++++++++++++---
>  t/t7800-difftool.sh            | 14 ++++++++++++++
>  3 files changed, 35 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/git-difftool.txt b/Documentation/git-difftool.txt
> index e575fea..8361e6e 100644
> --- a/Documentation/git-difftool.txt
> +++ b/Documentation/git-difftool.txt
> @@ -72,7 +72,9 @@ with custom merge tool commands and has the same value as `$MERGED`.
>  --symlinks::
>  --no-symlinks::
>         'git difftool''s default behavior is create symlinks to the
> -       working tree when run in `--dir-diff` mode.
> +       working tree when run in `--dir-diff` mode and the right-hand
> +       side of the comparison yields the same content as the file in
> +       the working tree.
>  +
>  Specifying `--no-symlinks` instructs 'git difftool' to create copies
>  instead.  `--no-symlinks` is the default on Windows.
> diff --git a/git-difftool.perl b/git-difftool.perl
> index 0a90de4..5f093ae 100755
> --- a/git-difftool.perl
> +++ b/git-difftool.perl
> @@ -83,6 +83,21 @@ sub exit_cleanup
>         exit($status | ($status >> 8));
>  }
>
> +sub use_wt_file
> +{
> +       my ($repo, $workdir, $file, $sha1, $symlinks) = @_;
> +       my $null_sha1 = '0' x 40;
> +
> +       if ($sha1 eq $null_sha1) {
> +               return 1;
> +       } elsif (not $symlinks) {
> +               return 0;
> +       }
> +
> +       my $wt_sha1 = $repo->command_oneline('hash-object', "$workdir/$file");
> +       return $sha1 eq $wt_sha1;
> +}
> +
>  sub setup_dir_diff
>  {
>         my ($repo, $workdir, $symlinks) = @_;
> @@ -159,10 +174,10 @@ EOF
>                 }
>
>                 if ($rmode ne $null_mode) {
> -                       if ($rsha1 ne $null_sha1) {
> -                               $rindex .= "$rmode $rsha1\t$dst_path\0";
> -                       } else {
> +                       if (use_wt_file($repo, $workdir, $dst_path, $rsha1, $symlinks)) {
>                                 push(@working_tree, $dst_path);
> +                       } else {
> +                               $rindex .= "$rmode $rsha1\t$dst_path\0";
>                         }
>                 }
>         }
> diff --git a/t/t7800-difftool.sh b/t/t7800-difftool.sh
> index eb1d3f8..8102ce1 100755
> --- a/t/t7800-difftool.sh
> +++ b/t/t7800-difftool.sh
> @@ -370,6 +370,20 @@ test_expect_success PERL 'difftool --dir-diff' '
>         echo "$diff" | stdin_contains file
>  '
>
> +write_script .git/CHECK_SYMLINKS <<\EOF &&

> +#!/bin/sh
> +test -L "$2/file" &&
> +test -L "$2/file2" &&
> +test -L "$2/sub/sub"
> +echo $?
> +EOF
> +
> +test_expect_success PERL,SYMLINKS 'difftool --dir-diff --symlink without unstaged changes' '
> +       result=$(git difftool --dir-diff --symlink \
> +               --extcmd "./.git/CHECK_SYMLINKS" branch HEAD) &&
> +       test "$result" = 0
> +'
> +