[PATCH 1/2] add_to_alternates_file: don't add duplicate paths

[Jim Hill <gjthill@gmail.com>]

Check for an existing match before appending a path to the alternates
file.  Beyond making git look smart to anyone checking the alternates
file, this removes the last use of hold_lock_file_for_append.

Signed-off-by: Jim Hill <gjthill@gmail.com>
---
 sha1_file.c                | 29 +++++++++++++++++++++++++----
 t/t5700-clone-reference.sh |  4 ++--
 2 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/sha1_file.c b/sha1_file.c
index 47f56f2..43d9530 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -403,14 +403,35 @@ void read_info_alternates(const char * relative_base, int depth)
 
 void add_to_alternates_file(const char *reference)
 {
-	struct lock_file *lock = xcalloc(1, sizeof(struct lock_file));
-	int fd = hold_lock_file_for_append(lock, git_path("objects/info/alternates"), LOCK_DIE_ON_ERROR);
+	static struct lock_file lock = {0};
 	char *alt = mkpath("%s\n", reference);
+	char *alts = git_path("objects/info/alternates");
+	int fd = hold_lock_file_for_update(&lock, alts, LOCK_DIE_ON_ERROR);
+	struct strbuf altdata = STRBUF_INIT;
+	struct string_list lines = STRING_LIST_INIT_NODUP;
+
+	if (strbuf_read_file(&altdata, alts, 0) < 0)
+		if (errno != ENOENT)
+			die("alternates file unreadable");
+	strbuf_complete_line(&altdata);
+	write_or_die(fd, altdata.buf, altdata.len);
+
+	string_list_split_in_place(&lines, altdata.buf, '\n', -1);
+	lines.cmp = strcmp_icase;
+	if (unsorted_string_list_has_string(&lines, reference)) {
+		rollback_lock_file(&lock);
+		goto cleanup;
+	}
+
 	write_or_die(fd, alt, strlen(alt));
-	if (commit_lock_file(lock))
-		die("could not close alternates file");
+	if (commit_lock_file(&lock))
+		die("could not update alternates file");
 	if (alt_odb_tail)
 		link_alt_odb_entries(alt, strlen(alt), '\n', NULL, 0);
+
+cleanup:
+	strbuf_reset(&altdata);
+	string_list_clear(&lines,0);
 }
 
 int foreach_alt_odb(alt_odb_fn fn, void *cb)
diff --git a/t/t5700-clone-reference.sh b/t/t5700-clone-reference.sh
index 3e783fc..cd9fa34 100755
--- a/t/t5700-clone-reference.sh
+++ b/t/t5700-clone-reference.sh
@@ -29,11 +29,11 @@ git prune'
 cd "$base_dir"
 
 test_expect_success 'cloning with reference (-l -s)' \
-'git clone -l -s --reference B A C'
+'git clone -l -s --reference B --reference A --reference B A C'
 
 cd "$base_dir"
 
-test_expect_success 'existence of info/alternates' \
+test_expect_success 'existence of info/alternates, no duplicates' \
 'test_line_count = 2 C/.git/objects/info/alternates'
 
 cd "$base_dir"
-- 
2.4.1.4.gfc728c2