builtin/merge-base: free commit lists

In several functions, we iterate through a commit list by assigning
`result = result->next`. As a consequence, we lose the original pointer
and eventually leak the list.

Rewrite the loops so that we keep the original pointers, then call
`free_commit_list()`. Various alternatives were considered:

1) Use `UNLEAK(result)` before the loop. Simple change, but not very
pretty. These would definitely be new lows among our usages of UNLEAK.
2) Use `pop_commit()` when looping. Slightly less simple change, but it
feels slightly preferable to first display the list, then free it.
3) As in this patch, but with `UNLEAK()` instead of freeing. We'd still
go through all the trouble of refactoring the loop, and because it's not
super-obvious that we're about to exit, let's just free the lists -- it
probably doesn't affect the runtime much.

In `handle_independent()` we can drop `result` while we're here and
reuse the `revs`-variable instead. That matches several other users of
`reduce_heads()`. The memory-leak that this hides will be addressed in
the next commit.

Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/merge-base.c

@@ -9,20 +9,20 @@
 
 static int show_merge_base(struct commit **rev, int rev_nr, int show_all)
 {
-	struct commit_list *result;
+	struct commit_list *result, *r;
 
 	result = get_merge_bases_many_dirty(rev[0], rev_nr - 1, rev + 1);
 
 	if (!result)
 		return 1;
 
-	while (result) {
-		printf("%s\n", oid_to_hex(&result->item->object.oid));
+	for (r = result; r; r = r->next) {
+		printf("%s\n", oid_to_hex(&r->item->object.oid));
 		if (!show_all)
-			return 0;
-		result = result->next;
+			break;
 	}
 
+	free_commit_list(result);
 	return 0;
 }
 
@@ -51,28 +51,28 @@ static struct commit *get_commit_reference(const char *arg)
 
 static int handle_independent(int count, const char **args)
 {
-	struct commit_list *revs = NULL;
-	struct commit_list *result;
+	struct commit_list *revs = NULL, *rev;
 	int i;
 
 	for (i = count - 1; i >= 0; i--)
 		commit_list_insert(get_commit_reference(args[i]), &revs);
 
-	result = reduce_heads(revs);
-	if (!result)
+	revs = reduce_heads(revs);
+
+	if (!revs)
 		return 1;
 
-	while (result) {
-		printf("%s\n", oid_to_hex(&result->item->object.oid));
-		result = result->next;
-	}
+	for (rev = revs; rev; rev = rev->next)
+		printf("%s\n", oid_to_hex(&rev->item->object.oid));
+
+	free_commit_list(revs);
 	return 0;
 }
 
 static int handle_octopus(int count, const char **args, int show_all)
 {
 	struct commit_list *revs = NULL;
-	struct commit_list *result;
+	struct commit_list *result, *rev;
 	int i;
 
 	for (i = count - 1; i >= 0; i--)
@@ -83,13 +83,13 @@ static int handle_octopus(int count, const char **args, int show_all)
 	if (!result)
 		return 1;
 
-	while (result) {
-		printf("%s\n", oid_to_hex(&result->item->object.oid));
+	for (rev = result; rev; rev = rev->next) {
+		printf("%s\n", oid_to_hex(&rev->item->object.oid));
 		if (!show_all)
-			return 0;
-		result = result->next;
+			break;
 	}
 
+	free_commit_list(result);
 	return 0;
 }