Re: [PATCH] difftool: Make directory diff symlink work tree

[John Keeping <john@keeping.me.uk>]

> difftool -d formerly knew how to symlink to the work tree when the work
> tree contains uncommitted changes. In practice, prior to this change, it
> would not symlink to the work tree in case there were no uncommitted
> changes, even when the user invoked difftool with the form:
> 
>     git difftool -d [--options] <commit> [--] [<path>...]
>         This form is to view the changes you have in your working tree
>         relative to the named <commit>. You can use HEAD to compare it
>         with the latest commit, or a branch name to compare with the tip
>         of a different branch.
> 
> Instead, prior to this change, difftool would use the file's HEAD blob
> sha1 to find its content rather than the work tree content. This change
> teaches `git diff --raw` to emit the null SHA1 for consumption by
> difftool -d, so that difftool -d will use a symlink rather than a copy
> of the file.
> 
> Before:
> 
>     $ git diff --raw HEAD^ -- diff-lib.c
>     :100644 100644 f35de0f... ead9399... M  diff-lib.c
> 
> After:
> 
>     $ ./git diff --raw HEAD^ -- diff-lib.c
>     :100644 100644 f35de0f... 0000000... M  diff-lib.c

When I tried this I got the expected behaviour even without this patch.

It turns out that an uncommitted, but *staged* change emits the SHA1 of
the blob rather than the null SHA1.  Do you get the desired behaviour if
you "git reset" before using difftool?

If so I think you want some new mode of operation for difftool instead
of this patch which will also affect unrelated commands.

> ---
>  diff-lib.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/diff-lib.c b/diff-lib.c
> index f35de0f..ead9399 100644
> --- a/diff-lib.c
> +++ b/diff-lib.c
> @@ -319,6 +319,10 @@ static int show_modified(struct rev_info *revs,
>  		return -1;
>  	}
>  
> +	if (!cached && hashcmp(old->sha1, new->sha1)) {
> +		sha1 = null_sha1;
> +	}
> +
>  	if (revs->combine_merges && !cached &&
>  	    (hashcmp(sha1, old->sha1) || hashcmp(old->sha1, new->sha1))) {
>  		struct combine_diff_path *p;
> -- 
> 1.8.2.rc2.4.g7799588
>