Merge branch 'jk/git-path'

git_path() and mkpath() are handy helper functions but it is easy
to misuse, as the callers need to be careful to keep the number of
active results below 4.  Their uses have been reduced.

* jk/git-path:
  memoize common git-path "constant" files
  get_repo_path: refactor path-allocation
  find_hook: keep our own static buffer
  refs.c: remove_empty_directories can take a strbuf
  refs.c: avoid git_path assignment in lock_ref_sha1_basic
  refs.c: avoid repeated git_path calls in rename_tmp_log
  refs.c: simplify strbufs in reflog setup and writing
  path.c: drop git_path_submodule
  refs.c: remove extra git_path calls from read_loose_refs
  remote.c: drop extraneous local variable from migrate_file
  prefer mkpathdup to mkpath in assignments
  prefer git_pathdup to git_path in some possibly-dangerous cases
  add_to_alternates_file: don't add duplicate entries
  t5700: modernize style
  cache.h: complete set of git_path_submodule helpers
  cache.h: clarify documentation for git_path, et al

1 files changed, 40 insertions, 7 deletions

diff --git a/sha1_file.c b/sha1_file.c
index 1081b95..ea78ba7 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -404,13 +404,46 @@ 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);
-	const char *alt = mkpath("%s\n", reference);
-	write_or_die(fd, alt, strlen(alt));
-	if (commit_lock_file(lock))
-		die("could not close alternates file");
-	if (alt_odb_tail)
-		link_alt_odb_entries(alt, strlen(alt), '\n', NULL, 0);
+	char *alts = git_pathdup("objects/info/alternates");
+	FILE *in, *out;
+
+	hold_lock_file_for_update(lock, alts, LOCK_DIE_ON_ERROR);
+	out = fdopen_lock_file(lock, "w");
+	if (!out)
+		die_errno("unable to fdopen alternates lockfile");
+
+	in = fopen(alts, "r");
+	if (in) {
+		struct strbuf line = STRBUF_INIT;
+		int found = 0;
+
+		while (strbuf_getline(&line, in, '\n') != EOF) {
+			if (!strcmp(reference, line.buf)) {
+				found = 1;
+				break;
+			}
+			fprintf_or_die(out, "%s\n", line.buf);
+		}
+
+		strbuf_release(&line);
+		fclose(in);
+
+		if (found) {
+			rollback_lock_file(lock);
+			lock = NULL;
+		}
+	}
+	else if (errno != ENOENT)
+		die_errno("unable to read alternates file");
+
+	if (lock) {
+		fprintf_or_die(out, "%s\n", reference);
+		if (commit_lock_file(lock))
+			die_errno("unable to move new alternates file into place");
+		if (alt_odb_tail)
+			link_alt_odb_entries(reference, strlen(reference), '\n', NULL, 0);
+	}
+	free(alts);
 }
 
 int foreach_alt_odb(alt_odb_fn fn, void *cb)