commit: simplify building parents list

Push pptr down into the FROM_MERGE branch of the if/else statement,
where it's actually used, and call commit_list_append() for appending
elements instead of playing tricks with commit_list_insert().  Call
copy_commit_list() in the amend branch instead of open-coding it.  Don't
bother setting pptr in the final branch as it's not used thereafter.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/commit.c

@@ -1639,7 +1639,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 	const char *index_file, *reflog_msg;
 	char *nl;
 	unsigned char sha1[20];
-	struct commit_list *parents = NULL, **pptr = &parents;
+	struct commit_list *parents = NULL;
 	struct stat statbuf;
 	struct commit *current_head = NULL;
 	struct commit_extra_header *extra = NULL;
@@ -1681,20 +1681,18 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 		if (!reflog_msg)
 			reflog_msg = "commit (initial)";
 	} else if (amend) {
-		struct commit_list *c;
-
 		if (!reflog_msg)
 			reflog_msg = "commit (amend)";
-		for (c = current_head->parents; c; c = c->next)
-			pptr = &commit_list_insert(c->item, pptr)->next;
+		parents = copy_commit_list(current_head->parents);
 	} else if (whence == FROM_MERGE) {
 		struct strbuf m = STRBUF_INIT;
 		FILE *fp;
 		int allow_fast_forward = 1;
+		struct commit_list **pptr = &parents;
 
 		if (!reflog_msg)
 			reflog_msg = "commit (merge)";
-		pptr = &commit_list_insert(current_head, pptr)->next;
+		pptr = commit_list_append(current_head, pptr);
 		fp = fopen(git_path_merge_head(), "r");
 		if (fp == NULL)
 			die_errno(_("could not open '%s' for reading"),
@@ -1705,7 +1703,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 			parent = get_merge_parent(m.buf);
 			if (!parent)
 				die(_("Corrupt MERGE_HEAD file (%s)"), m.buf);
-			pptr = &commit_list_insert(parent, pptr)->next;
+			pptr = commit_list_append(parent, pptr);
 		}
 		fclose(fp);
 		strbuf_release(&m);
@@ -1722,7 +1720,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 			reflog_msg = (whence == FROM_CHERRY_PICK)
 					? "commit (cherry-pick)"
 					: "commit";
-		pptr = &commit_list_insert(current_head, pptr)->next;
+		commit_list_insert(current_head, &parents);
 	}
 
 	/* Finally, get the commit message */