revision: provide implementation for diff merges tweaks

Use these implementations from show_setup_revisions_tweak() and
log_setup_revisions_tweak() in builtin/log.c.

This completes moving of management of diff merges parameters to a
single place, where we can finally observe them simultaneously.

Signed-off-by: Sergey Organov <sorganov@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/log.c

@@ -598,15 +598,7 @@ static int show_tree_object(const struct object_id *oid,
 static void show_setup_revisions_tweak(struct rev_info *rev,
 				       struct setup_revision_opt *opt)
 {
-	if (rev->ignore_merges < 0) {
-		/* There was no "-m" variant on the command line */
-		rev->ignore_merges = 0;
-		if (!rev->first_parent_only && !rev->combine_merges) {
-			/* No "--first-parent", "-c", or "--cc" */
-			rev->combine_merges = 1;
-			rev->dense_combined_merges = 1;
-		}
-	}
+	rev_diff_merges_default_to_dense_combined(rev);
 	if (!rev->diffopt.output_format)
 		rev->diffopt.output_format = DIFF_FORMAT_PATCH;
 }
@@ -731,8 +723,7 @@ static void log_setup_revisions_tweak(struct rev_info *rev,
 	if (!rev->diffopt.output_format && rev->combine_merges)
 		rev->diffopt.output_format = DIFF_FORMAT_PATCH;
 
-	if (rev->first_parent_only && rev->ignore_merges < 0)
-		rev->ignore_merges = 0;
+	rev_diff_merges_first_parent_defaults_to_enable(rev);
 }
 
 int cmd_log(int argc, const char **argv, const char *prefix)

revision.c

@@ -2209,6 +2209,25 @@ static void setup_diff_merges_revs(struct rev_info *revs)
 		die("--combined-all-paths makes no sense without -c or --cc");
 }
 
+void rev_diff_merges_first_parent_defaults_to_enable(struct rev_info *revs)
+{
+	if (revs->first_parent_only && revs->ignore_merges < 0)
+		revs->ignore_merges = 0;
+}
+
+void rev_diff_merges_default_to_dense_combined(struct rev_info *revs)
+{
+	if (revs->ignore_merges < 0) {
+		/* There was no "-m" variant on the command line */
+		revs->ignore_merges = 0;
+		if (!revs->first_parent_only && !revs->combine_merges) {
+			/* No "--first-parent", "-c", or "--cc" */
+			revs->combine_merges = 1;
+			revs->dense_combined_merges = 1;
+		}
+	}
+}
+
 static int handle_revision_opt(struct rev_info *revs, int argc, const char **argv,
 			       int *unkc, const char **unkv,
 			       const struct setup_revision_opt* opt)

revision.h

@@ -456,4 +456,7 @@ int rewrite_parents(struct rev_info *revs,
  */
 struct commit_list *get_saved_parents(struct rev_info *revs, const struct commit *commit);
 
+void rev_diff_merges_default_to_dense_combined(struct rev_info *revs);
+void rev_diff_merges_first_parent_defaults_to_enable(struct rev_info *revs);
+
 #endif