git: update to v2.18.0

Update to git version v2.18.0. Required changes follow upstream commits:

* Convert find_unique_abbrev* to struct object_id
  (aab9583f7b5ea5463eb3f653a0b4ecac7539dc94)
* sha1_file: convert read_sha1_file to struct object_id
  (b4f5aca40e6f77cbabcbf4ff003c3cf30a1830c8)
* sha1_file: convert sha1_object_info* to object_id
  (abef9020e3df87c441c9a3a95f592fce5fa49bb9)
* object-store: move packed_git and packed_git_mru to object store
  (a80d72db2a73174b3f22142eb2014b33696fd795)
* treewide: rename tree to maybe_tree
  (891435d55da80ca3654b19834481205be6bdfe33)

The changed data types required some of our own functions to be converted
to struct object_id:

  ls_item
  print_dir
  print_dir_entry
  print_object
  single_tree_cb
  walk_tree
  write_tree_link

And finally we use new upstream functions that were added for
struct object_id:

  hashcpy     -> oidcpy
  sha1_to_hex -> oid_to_hex

Signed-off-by: Christian Hesse <mail@eworm.de>
Reviewed-by: John Keeping <john@keeping.me.uk>

ui-blob.c

@@ -18,7 +18,7 @@ struct walk_tree_context {
 	unsigned int file_only:1;
 };
 
-static int walk_tree(const unsigned char *sha1, struct strbuf *base,
+static int walk_tree(const struct object_id *oid, struct strbuf *base,
 		const char *pathname, unsigned mode, int stage, void *cbdata)
 {
 	struct walk_tree_context *walk_tree_ctx = cbdata;
@@ -28,7 +28,7 @@ static int walk_tree(const unsigned char *sha1, struct strbuf *base,
 	if (strncmp(base->buf, walk_tree_ctx->match_path, base->len)
 		|| strcmp(walk_tree_ctx->match_path + base->len, pathname))
 		return READ_TREE_RECURSIVE;
-	hashcpy(walk_tree_ctx->matched_oid->hash, sha1);
+	oidcpy(walk_tree_ctx->matched_oid, oid);
 	walk_tree_ctx->found_path = 1;
 	return 0;
 }
@@ -54,9 +54,9 @@ int cgit_ref_path_exists(const char *path, const char *ref, int file_only)
 
 	if (get_oid(ref, &oid))
 		goto done;
-	if (sha1_object_info(oid.hash, &size) != OBJ_COMMIT)
+	if (oid_object_info(the_repository, &oid, &size) != OBJ_COMMIT)
 		goto done;
-	read_tree_recursive(lookup_commit_reference(&oid)->tree, "", 0, 0, &paths, walk_tree, &walk_tree_ctx);
+	read_tree_recursive(lookup_commit_reference(&oid)->maybe_tree, "", 0, 0, &paths, walk_tree, &walk_tree_ctx);
 
 done:
 	free(path_items.match);
@@ -87,17 +87,17 @@ int cgit_print_file(char *path, const char *head, int file_only)
 
 	if (get_oid(head, &oid))
 		return -1;
-	type = sha1_object_info(oid.hash, &size);
+	type = oid_object_info(the_repository, &oid, &size);
 	if (type == OBJ_COMMIT) {
 		commit = lookup_commit_reference(&oid);
-		read_tree_recursive(commit->tree, "", 0, 0, &paths, walk_tree, &walk_tree_ctx);
+		read_tree_recursive(commit->maybe_tree, "", 0, 0, &paths, walk_tree, &walk_tree_ctx);
 		if (!walk_tree_ctx.found_path)
 			return -1;
-		type = sha1_object_info(oid.hash, &size);
+		type = oid_object_info(the_repository, &oid, &size);
 	}
 	if (type == OBJ_BAD)
 		return -1;
-	buf = read_sha1_file(oid.hash, &type, &size);
+	buf = read_object_file(&oid, &type, &size);
 	if (!buf)
 		return -1;
 	buf[size] = '\0';
@@ -142,12 +142,12 @@ void cgit_print_blob(const char *hex, char *path, const char *head, int file_onl
 		}
 	}
 
-	type = sha1_object_info(oid.hash, &size);
+	type = oid_object_info(the_repository, &oid, &size);
 
 	if ((!hex) && type == OBJ_COMMIT && path) {
 		commit = lookup_commit_reference(&oid);
-		read_tree_recursive(commit->tree, "", 0, 0, &paths, walk_tree, &walk_tree_ctx);
-		type = sha1_object_info(oid.hash, &size);
+		read_tree_recursive(commit->maybe_tree, "", 0, 0, &paths, walk_tree, &walk_tree_ctx);
+		type = oid_object_info(the_repository, &oid, &size);
 	}
 
 	if (type == OBJ_BAD) {
@@ -156,7 +156,7 @@ void cgit_print_blob(const char *hex, char *path, const char *head, int file_onl
 		return;
 	}
 
-	buf = read_sha1_file(oid.hash, &type, &size);
+	buf = read_object_file(&oid, &type, &size);
 	if (!buf) {
 		cgit_print_error_page(500, "Internal server error",
 				"Error reading object %s", hex);