Re: [PATCH 1/2] pretty: add %(describe)

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

On Sun, Feb 14 2021, René Scharfe wrote:

> +'%(describe)':: human-readable name, like linkgit:git-describe[1];
> +		empty string for undescribable commits

In the case of undescribable we've got the subcommand exiting non-zero
and we ignore it. The right thing in this case given how the rest of
format arguments work, but maybe something to explicitly test for?
>
> +	if (skip_prefix(placeholder, "(describe)", &arg)) {
> +		struct child_process cmd = CHILD_PROCESS_INIT;
> +		struct strbuf out = STRBUF_INIT;
> +		struct strbuf err = STRBUF_INIT;
> +
> +		cmd.git_cmd = 1;
> +		strvec_push(&cmd.args, "describe");
> +		strvec_push(&cmd.args, oid_to_hex(&commit->object.oid));
> +		pipe_command(&cmd, NULL, 0, &out, 0, &err, 0);
> +		strbuf_rtrim(&out);
> +		strbuf_addbuf(sb, &out);
> +		strbuf_release(&out);
> +		strbuf_release(&err);
> +		return arg - placeholder;
> +	}

There's another edge case in this: if you do "%(describe)%(describe)"
it'll be run twice for the rev, 3 times if you add another "%(describe)"
etc. I don't know if pretty.c has an easy way to cache/avoid that.