Revert 4b7f53da (simplify-merges: drop merge from irrelevant side branch, 2013-01-17)

Kevin Bracey reports that the change regresses a case shown in the
user manual.

Trading one fix with another breakage is not worth it.  Just keep
the test to document the existing breakage, and revert the change
for now.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

revision.c

@@ -1970,22 +1970,6 @@ static struct merge_simplify_state *locate_simplify_state(struct rev_info *revs,
 	return st;
 }
 
-static void remove_treesame_parents(struct commit *commit)
-{
-	struct commit_list **pp, *p;
-
-	pp = &commit->parents;
-	while ((p = *pp) != NULL) {
-		struct commit *parent = p->item;
-		if (parent->object.flags & TREESAME) {
-			*pp = p->next;
-			free(p);
-			continue;
-		}
-		pp = &p->next;
-	}
-}
-
 static struct commit_list **simplify_one(struct rev_info *revs, struct commit *commit, struct commit_list **tail)
 {
 	struct commit_list *p;
@@ -2039,17 +2023,10 @@ static struct commit_list **simplify_one(struct rev_info *revs, struct commit *c
 			break;
 	}
 
-	if (revs->first_parent_only) {
+	if (revs->first_parent_only)
 		cnt = 1;
-	} else {
-		/*
-		 * A merge with a tree-same parent is useless
-		 */
-		if (commit->parents && commit->parents->next)
-			remove_treesame_parents(commit);
-
+	else
 		cnt = remove_duplicate_parents(commit);
-	}
 
 	/*
 	 * It is possible that we are a merge and one side branch

t/t6012-rev-list-simplify.sh

@@ -77,14 +77,16 @@ test_expect_success setup '
 
 FMT='tformat:%P 	%H | %s'
 
-check_result () {
+check_outcome () {
+	outcome=$1
+	shift
 	for c in $1
 	do
 		echo "$c"
 	done >expect &&
 	shift &&
 	param="$*" &&
-	test_expect_success "log $param" '
+	test_expect_$outcome "log $param" '
 		git log --pretty="$FMT" --parents $param |
 		unnote >actual &&
 		sed -e "s/^.*	\([^ ]*\) .*/\1/" >check <actual &&
@@ -95,11 +97,15 @@ check_result () {
 	'
 }
 
+check_result () {
+	check_outcome success "$@"
+}
+
 check_result 'L K J I H G F E D C B A' --full-history
 check_result 'K I H E C B A' --full-history -- file
 check_result 'K I H E C B A' --full-history --topo-order -- file
 check_result 'K I H E C B A' --full-history --date-order -- file
-check_result 'I E C B A' --simplify-merges -- file
+check_outcome failure 'I E C B A' --simplify-merges -- file
 check_result 'I B A' -- file
 check_result 'I B A' --topo-order -- file
 check_result 'H' --first-parent -- another-file