[PATCH 03/14] format-patch: teach --interdiff to respect -v/--reroll-count

[Eric Sunshine]

The --interdiff option introduces the embedded interdiff generically as
"Interdiff:", however, we can do better when --reroll-count is specified
by emitting "Interdiff against v{n}:" instead.

Signed-off-by: Eric Sunshine <sunsh...@sunshineco.com>
---
 builtin/log.c           | 17 ++++++++++++++++-
 revision.h              |  1 +
 t/t4014-format-patch.sh |  5 +++++
 3 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/builtin/log.c b/builtin/log.c
index 1020b78477..99ddfe8bb0 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -1085,7 +1085,7 @@ static void make_cover_letter(struct rev_info *rev, int 
use_stdout,
                show_diffstat(rev, origin, head);
 
        if (rev->idiff_oid1) {
-               fprintf_ln(rev->diffopt.file, "%s", _("Interdiff:"));
+               fprintf_ln(rev->diffopt.file, "%s", rev->idiff_title);
                show_interdiff(rev);
        }
 }
@@ -1427,6 +1427,16 @@ static void print_bases(struct base_tree_info *bases, 
FILE *file)
        oidclr(&bases->base_commit);
 }
 
+static const char *diff_title(struct strbuf *sb, int reroll_count,
+                      const char *generic, const char *rerolled)
+{
+       if (reroll_count <= 0)
+               strbuf_addstr(sb, generic);
+       else /* RFC may be v0, so allow -v1 to diff against v0 */
+               strbuf_addf(sb, rerolled, reroll_count - 1);
+       return sb->buf;
+}
+
 int cmd_format_patch(int argc, const char **argv, const char *prefix)
 {
        struct commit *commit;
@@ -1455,6 +1465,7 @@ int cmd_format_patch(int argc, const char **argv, const 
char *prefix)
        int show_progress = 0;
        struct progress *progress = NULL;
        struct oid_array idiff_prev = OID_ARRAY_INIT;
+       struct strbuf idiff_title = STRBUF_INIT;
 
        const struct option builtin_format_patch_options[] = {
                { OPTION_CALLBACK, 'n', "numbered", &numbered, NULL,
@@ -1758,6 +1769,9 @@ int cmd_format_patch(int argc, const char **argv, const 
char *prefix)
                        die(_("--interdiff requires --cover-letter"));
                rev.idiff_oid1 = &idiff_prev.oid[idiff_prev.nr - 1];
                rev.idiff_oid2 = get_commit_tree_oid(list[0]);
+               rev.idiff_title = diff_title(&idiff_title, reroll_count,
+                                            _("Interdiff:"),
+                                            _("Interdiff against v%d:"));
        }
 
        if (!signature) {
@@ -1880,6 +1894,7 @@ int cmd_format_patch(int argc, const char **argv, const 
char *prefix)
 
 done:
        oid_array_clear(&idiff_prev);
+       strbuf_release(&idiff_title);
        return 0;
 }
 
diff --git a/revision.h b/revision.h
index 61931fbac5..ffeadc261a 100644
--- a/revision.h
+++ b/revision.h
@@ -215,6 +215,7 @@ struct rev_info {
        /* interdiff */
        const struct object_id *idiff_oid1;
        const struct object_id *idiff_oid2;
+       const char *idiff_title;
 
        /* commit counts */
        int count_left;
diff --git a/t/t4014-format-patch.sh b/t/t4014-format-patch.sh
index 57b46322aa..5950890d30 100755
--- a/t/t4014-format-patch.sh
+++ b/t/t4014-format-patch.sh
@@ -1734,4 +1734,9 @@ test_expect_success 'interdiff: cover-letter' '
        test_cmp expect actual
 '
 
+test_expect_success 'interdiff: reroll-count' '
+       git format-patch --cover-letter --interdiff=boop~2 -v2 -1 boop &&
+       test_i18ngrep "^Interdiff ..* v1:$" v2-0000-cover-letter.patch
+'
+
 test_done
-- 
2.18.0.345.g5c9ce644c3