[PATCH 2/3] diff-lib: tighten show_interdiff()'s interface

[Eric Sunshine <sunshine@sunshineco.com>]

To compute and show an interdiff, show_interdiff() needs only the two
OID's to compare and a diffopts, yet it expects callers to supply an
entire rev_info. The demand for rev_info is not only overkill, but also
places unnecessary burden on potential future callers which might not
otherwise have a rev_info at hand. Address this by tightening its
signature to require only the items it needs instead of a full rev_info.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
---

Notes:
    Suggested by Sunshine[1] during review.
    
    [1]: https://lore.kernel.org/git/CAPig+cSuYUYSPTuKx08wcmQM-G12_-W2T4BS07fA=6grM1b8Gw@mail.gmail.com/

 builtin/log.c | 3 ++-
 diff-lib.c    | 7 ++++---
 diff.h        | 7 ++++++-
 log-tree.c    | 3 ++-
 4 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/builtin/log.c b/builtin/log.c
index ae9380da1b..37177b3e7f 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -1206,7 +1206,8 @@ static void make_cover_letter(struct rev_info *rev, int use_stdout,
 
 	if (rev->idiff_oid1) {
 		fprintf_ln(rev->diffopt.file, "%s", rev->idiff_title);
-		show_interdiff(rev, 0);
+		show_interdiff(rev->idiff_oid1, rev->idiff_oid2, 0,
+			       &rev->diffopt);
 	}
 
 	if (rev->rdiff1) {
diff --git a/diff-lib.c b/diff-lib.c
index 9bab907412..a17becc509 100644
--- a/diff-lib.c
+++ b/diff-lib.c
@@ -577,19 +577,20 @@ static struct strbuf *idiff_prefix_cb(struct diff_options *opt, void *data)
 	return data;
 }
 
-void show_interdiff(struct rev_info *rev, int indent)
+void show_interdiff(const struct object_id *oid1, const struct object_id *oid2,
+		    int indent, struct diff_options *diffopt)
 {
 	struct diff_options opts;
 	struct strbuf prefix = STRBUF_INIT;
 
-	memcpy(&opts, &rev->diffopt, sizeof(opts));
+	memcpy(&opts, diffopt, sizeof(opts));
 	opts.output_format = DIFF_FORMAT_PATCH;
 	opts.output_prefix = idiff_prefix_cb;
 	strbuf_addchars(&prefix, ' ', indent);
 	opts.output_prefix_data = &prefix;
 	diff_setup_done(&opts);
 
-	diff_tree_oid(rev->idiff_oid1, rev->idiff_oid2, "", &opts);
+	diff_tree_oid(oid1, oid2, "", &opts);
 	diffcore_std(&opts);
 	diff_flush(&opts);
 
diff --git a/diff.h b/diff.h
index 308937c94b..49242d2733 100644
--- a/diff.h
+++ b/diff.h
@@ -600,7 +600,12 @@ int index_differs_from(struct repository *r, const char *def,
 		       const struct diff_flags *flags,
 		       int ita_invisible_in_index);
 
-void show_interdiff(struct rev_info *, int indent);
+/*
+ * Emit an interdiff of two object ID's to 'diff_options.file' optionally
+ * indented by 'indent' spaces.
+ */
+void show_interdiff(const struct object_id *, const struct object_id *,
+		    int indent, struct diff_options *);
 
 /*
  * Fill the contents of the filespec "df", respecting any textconv defined by
diff --git a/log-tree.c b/log-tree.c
index 39bb362d5e..ad1e7e31f8 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -799,7 +799,8 @@ void show_log(struct rev_info *opt)
 
 		next_commentary_block(opt, NULL);
 		fprintf_ln(opt->diffopt.file, "%s", opt->idiff_title);
-		show_interdiff(opt, 2);
+		show_interdiff(opt->idiff_oid1, opt->idiff_oid2, 2,
+			       &opt->diffopt);
 
 		memcpy(&diff_queued_diff, &dq, sizeof(diff_queued_diff));
 	}
-- 
2.28.0.618.gf4bc123cb7