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

[Jeff King <peff@peff.net>]

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