Re: Design of multiple hash support

[Duy Nguyen <pclouds@gmail.com>]

On Mon, Nov 5, 2018 at 2:02 AM brian m. carlson
<sandals@crustytoothpaste.net> wrote:
>
> I'm currently working on getting Git to support multiple hash algorithms
> in the same binary (SHA-1 and SHA-256).  In order to have a fully
> functional binary, we'll need to have some way of indicating to certain
> commands (such as init and show-index) that they should assume a certain
> hash algorithm.
>
> There are basically two approaches I can take.  The first is to provide
> each command that needs to learn about this with its own --hash
> argument.  So we'd have:
>
>   git init --hash=sha256
>   git show-index --hash=sha256 <some-file
>
> The other alternative is that we provide a global option to git, which
> is parsed by all programs, like so:
>
>   git --hash=sha256 init
>   git --hash=sha256 show-index <some-file
>

I suppose this is about the "no repository/standalone" mode, because

 - it's hard to pass global arguments down to builtin commands (we
often have to rely on global variables which are on the way out)

 - global options confuse new people and also harder to reorder (if
you forget it, you have to alt-b all the way back to near the
beginning of the command line and add it there, instead of near the
end)

 - there aren't that many standalone commands

I'm leaning towards "git foo --hash=".

> There's also the question of what we want to call the option.  The
> obvious name is --hash, which is intuitive and straightforward.
> However, the transition plan names the config option
> extensions.objectFormat, so --object-format is also a possibility.  If
> we ever decide to support, say, zstd compression instead of zlib, we
> could leverage the same option (say, --object-format=sha256:zstd) and
> avoid the need for an additional option.  This might be planning for a
> future that never occurs, though.

--object-format is less vague than --hash. The downside is it's longer
(more to type) but I'm counting on git-completion.bash and the guess
that people rarely need to use this option.
-- 
Duy