diff-merges: move checks for first_parent_only out of the module

The checks for first_parent_only don't in fact belong to this module,
as the primary purpose of this flag is history traversal limiting, so
get it out of this module and rename the

diff_merges_first_parent_defaults_to_enable()

to

diff_merges_default_to_enable()

to match new semantics.

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

builtin/log.c

@@ -599,7 +599,10 @@ 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)
 {
-	diff_merges_default_to_dense_combined(rev);
+	if (rev->first_parent_only)
+		diff_merges_default_to_enable(rev);
+	else
+		diff_merges_default_to_dense_combined(rev);
 	if (!rev->diffopt.output_format)
 		rev->diffopt.output_format = DIFF_FORMAT_PATCH;
 }
@@ -724,7 +727,8 @@ 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;
 
-	diff_merges_first_parent_defaults_to_enable(rev);
+	if (rev->first_parent_only)
+		diff_merges_default_to_enable(rev);
 }
 
 int cmd_log(int argc, const char **argv, const char *prefix)

diff-merges.c

@@ -56,19 +56,17 @@ void diff_merges_setup_revs(struct rev_info *revs)
 		die("--combined-all-paths makes no sense without -c or --cc");
 }
 
-void diff_merges_first_parent_defaults_to_enable(struct rev_info *revs)
+void diff_merges_default_to_enable(struct rev_info *revs)
 {
-	if (revs->first_parent_only && revs->ignore_merges < 0)
+	if (revs->ignore_merges < 0)		/* No -m */
 		revs->ignore_merges = 0;
 }
 
 void diff_merges_default_to_dense_combined(struct rev_info *revs)
 {
-	if (revs->ignore_merges < 0) {
-		/* There was no "-m" variant on the command line */
+	if (revs->ignore_merges < 0) {		/* No -m */
 		revs->ignore_merges = 0;
-		if (!revs->first_parent_only && !revs->combine_merges) {
-			/* No "--first-parent", "-c", or "--cc" */
+		if (!revs->combine_merges) {	/* No -c/--cc" */
 			revs->combine_merges = 1;
 			revs->dense_combined_merges = 1;
 		}

diff-merges.h

@@ -17,7 +17,7 @@ void diff_merges_setup_revs(struct rev_info *revs);
 
 void diff_merges_default_to_dense_combined(struct rev_info *revs);
 
-void diff_merges_first_parent_defaults_to_enable(struct rev_info *revs);
+void diff_merges_default_to_enable(struct rev_info *revs);
 
 
 #endif