[RFC PATCH 1/5] format-patch: allow additional generated content in make_cover_letter()

[Eric Sunshine <sunshine@sunshineco.com>]

make_cover_letter() returns early when it lacks sufficient state to emit
a diffstat, which makes it difficult to extend the function to reliably
emit additional generated content. Work around this shortcoming by
factoring diffstat-printing logic out to its own function and calling it
as needed without otherwise inhibiting normal control flow.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
---
 builtin/log.c | 43 +++++++++++++++++++++++--------------------
 1 file changed, 23 insertions(+), 20 deletions(-)

diff --git a/builtin/log.c b/builtin/log.c
index 71f68a3e4f..e01a256c11 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -992,6 +992,26 @@ static char *find_branch_name(struct rev_info *rev)
 	return branch;
 }
 
+static void emit_diffstat(struct rev_info *rev,
+			  struct commit *origin, struct commit *head)
+{
+	struct diff_options opts;
+
+	memcpy(&opts, &rev->diffopt, sizeof(opts));
+	opts.output_format = DIFF_FORMAT_SUMMARY | DIFF_FORMAT_DIFFSTAT;
+	opts.stat_width = MAIL_DEFAULT_WRAP;
+
+	diff_setup_done(&opts);
+
+	diff_tree_oid(&origin->tree->object.oid,
+		      &head->tree->object.oid,
+		      "", &opts);
+	diffcore_std(&opts);
+	diff_flush(&opts);
+
+	fprintf(rev->diffopt.file, "\n");
+}
+
 static void make_cover_letter(struct rev_info *rev, int use_stdout,
 			      struct commit *origin,
 			      int nr, struct commit **list,
@@ -1005,7 +1025,6 @@ static void make_cover_letter(struct rev_info *rev, int use_stdout,
 	struct strbuf sb = STRBUF_INIT;
 	int i;
 	const char *encoding = "UTF-8";
-	struct diff_options opts;
 	int need_8bit_cte = 0;
 	struct pretty_print_context pp = {0};
 	struct commit *head = list[0];
@@ -1055,25 +1074,9 @@ static void make_cover_letter(struct rev_info *rev, int use_stdout,
 
 	shortlog_output(&log);
 
-	/*
-	 * We can only do diffstat with a unique reference point
-	 */
-	if (!origin)
-		return;
-
-	memcpy(&opts, &rev->diffopt, sizeof(opts));
-	opts.output_format = DIFF_FORMAT_SUMMARY | DIFF_FORMAT_DIFFSTAT;
-	opts.stat_width = MAIL_DEFAULT_WRAP;
-
-	diff_setup_done(&opts);
-
-	diff_tree_oid(&origin->tree->object.oid,
-		      &head->tree->object.oid,
-		      "", &opts);
-	diffcore_std(&opts);
-	diff_flush(&opts);
-
-	fprintf(rev->diffopt.file, "\n");
+	/* We can only do diffstat with a unique reference point */
+	if (origin)
+		emit_diffstat(rev, origin, head);
 }
 
 static const char *clean_message_id(const char *msg_id)
-- 
2.17.1.1235.ge295dfb56e