Re: [feature] how to output absolute paths in git diff? => --show-abs-path

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

On Thu, Aug 23, 2018 at 11:16 AM Timothee Cour <thelastmammoth@gmail.com> wrote:
>
> This has all the context:
> https://stackoverflow.com/questions/22698505/how-to-show-full-paths-in-git-diff

It's helpful to copy it anyway, so we can discuss it here:

QUOTE

How do I show full paths in git diff? One can use '--dst-prefix=$PWD'
and '--src-prefix=$PWD' but this is fragile as it won't work in many
cases, eg with --no-index, or when running the commond from a
subdirectory without using --relative=realpath_to_cwd

END QUOTE

Wanting such a feature seems sensible. But I'm unclear on the details.

You say that --{src,dst}-prefix is fragile and doesn't work for
--no-index. But if I do this:

    (
    cd /tmp &&
    echo foo >a &&
    echo bar >b &&
    git --no-pager diff --src-prefix=$PWD/ --dst-prefix=$PWD/ a b
    )

I get this diff:

    diff --git /tmp/a /tmp/b
    new file mode 100644
    index 257cc56..5716ca5 100644
    --- /tmp/a
    +++ /tmp/b
    @@ -1 +1 @@
    -foo
    +bar

So this seems to work for --no-index, or if it doesn't what situations
doesn't it work in?

> I'd like `--show-abs-path` to show absolute paths in:
> git diff --show-abs-path args...
>
> eg:
> git diff --no-index `get_file1` `get_file2`
> could show:
> --- a/Users/timothee/temp/ripgrep/help0.txt
> +++ b/help1.txt

Is this a mistake, or would you only like --show-abs-paths to
implicitly supply --src-prefix, but not --dst-prefix? If so, why?

> * passing '--dst-prefix=$PWD' and '--src-prefix=$PWD' doesn't help
> because path arguments could be absolute, so it'll create
> $PWD/Users/timothee/temp/ripgrep/help0.txt (wrong)

Ah, so it's about supplying both the prefix *and* absolute paths,
whereas I see without --no-index we seem to handle this sort of thing
just fine:

    git diff --src-prefix=$PWD/ --dst-prefix=$PWD HEAD~.. $PWD/some-file

> * passing '--dst-prefix=.' will behave weirdly, replacing leading `/`
> by `.` (seems wrong)
> diff --git .Users/timothee/temp/ripgrep/help0.txt b/help1.txt

This is because the default prefixes are a/ and b/, respectively, and
the option allows you to entirely replace them. E.g. imagine needing
"../some-relative-path/"

> NOTE: I'm invoking the `git diff` command via a more complicated case
> (with multiple arguments including git diff flags and git diff files),
> so it's awkward for me to parse which arguments correspond to a file
> vs a flag (ie prevents easily converting input file arguments to
> absolute paths), but `git` could do it easily via a flag, eg
> `--show-abs-path`