Re: allow a differn't diff.context config for git format-patch

>
> On Tue, Apr 23, 2019 at 12:45:17PM +0900, Junio C Hamano wrote:
>
> > Jeff King <peff@peff.net> writes:
> >
> > > ... I don't think it would be
> > > too big a problem for format-patch to learn some options to configure
> > > its diffs. We already have some options in format.* for various things.
> >
> > I am not sure; diff.context is rather special in that the variable
> > behind it belongs to the diff layer and is set via diff_config that
> > is called by diff_ui_config that in turn is called by log_config
> > which is called by format_config.
> >
> > If we want to say "format.context" trumps "diff.config", then a new
> > internal variable to receive the value of the variable must be
> > invented and after the config gets read, cmd_format_patch() needs to
> > do something silly like this:
> >
> >                 git_config(git_format_config, NULL);
> >         +     if (format_context != -1)
> >         +             diff_default_context = format_context;
> >                 repo_init_revisions(the_repository, &rev, prefix);
> >
> > committing layering violation by exposing diff_default_context
> > variable.
>
> After init_revisions(), we'll have called diff_setup(), which puts
> diff_context_default into revs->diffopt. So we still have to do the "if
> we have a format-specific value, then override..." conditional. But we
> can do it without touching the hidden variable:
>
>
>

> diff --git a/builtin/log.c b/builtin/log.c
> index 57869267d8..0de2ee0905 100644
> --- a/builtin/log.c
> +++ b/builtin/log.c
> @@ -1613,14 +1613,16 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
>         repo_init_revisions(the_repository, &rev, prefix);
>         rev.commit_format = CMIT_FMT_EMAIL;
>         rev.expand_tabs_in_log_default = 0;
>         rev.verbose_header = 1;
>         rev.diff = 1;
>         rev.max_parents = 1;
>         rev.diffopt.flags.recursive = 1;
> +       if (format_context != -1)
> +               rev.diffopt.context = format_context;
>         rev.subject_prefix = fmt_patch_subject_prefix;
>         memset(&s_r_opt, 0, sizeof(s_r_opt));
>         s_r_opt.def = "HEAD";
>         s_r_opt.revarg_opt = REVARG_COMMITTISH;
>
>         if (default_attach) {
>                 rev.mime_boundary = default_attach;
>
> -Peff