tree.c: allow read_tree_recursive() to traverse gitlink entries

When the callback function invoked from read_tree_recursive() returns
the value `READ_TREE_RECURSIVE` for a gitlink entry, the traversal will
now continue into the tree connected to the gitlinked commit. This
functionality can be used to allow inter-repository operations, but
since the current users of read_tree_recursive() does not yet support
such operations, they have been modified where necessary to make sure
that they never return READ_TREE_RECURSIVE for gitlink entries (hence
no change in behaviour should be introduces by this patch alone).

Signed-off-by: Lars Hjemli <hjemli@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

archive.c

@@ -132,7 +132,7 @@ static int write_archive_entry(const unsigned char *sha1, const char *base,
 		err = write_entry(args, sha1, path.buf, path.len, mode, NULL, 0);
 		if (err)
 			return err;
-		return READ_TREE_RECURSIVE;
+		return (S_ISDIR(mode) ? READ_TREE_RECURSIVE : 0);
 	}
 
 	buffer = sha1_file_to_archive(path_without_prefix, sha1, mode,

builtin-ls-tree.c

@@ -68,13 +68,8 @@ static int show_tree(const unsigned char *sha1, const char *base, int baselen,
 		 *
 		 * Something similar to this incomplete example:
 		 *
-		if (show_subprojects(base, baselen, pathname)) {
-			struct child_process ls_tree;
-
-			ls_tree.dir = base;
-			ls_tree.argv = ls-tree;
-			start_command(&ls_tree);
-		}
+		if (show_subprojects(base, baselen, pathname))
+			retval = READ_TREE_RECURSIVE;
 		 *
 		 */
 		type = commit_type;

merge-recursive.c

@@ -237,7 +237,7 @@ static int save_files_dirs(const unsigned char *sha1,
 		string_list_insert(newpath, &o->current_file_set);
 	free(newpath);
 
-	return READ_TREE_RECURSIVE;
+	return (S_ISDIR(mode) ? READ_TREE_RECURSIVE : 0);
 }
 
 static int get_files_dirs(struct merge_options *o, struct tree *tree)

tree.c

@@ -131,6 +131,34 @@ int read_tree_recursive(struct tree *tree,
 			if (retval)
 				return -1;
 			continue;
+		} else if (S_ISGITLINK(entry.mode)) {
+			int retval;
+			struct strbuf path;
+			unsigned int entrylen;
+			struct commit *commit;
+
+			entrylen = tree_entry_len(entry.path, entry.sha1);
+			strbuf_init(&path, baselen + entrylen + 1);
+			strbuf_add(&path, base, baselen);
+			strbuf_add(&path, entry.path, entrylen);
+			strbuf_addch(&path, '/');
+
+			commit = lookup_commit(entry.sha1);
+			if (!commit)
+				die("Commit %s in submodule path %s not found",
+				    sha1_to_hex(entry.sha1), path.buf);
+
+			if (parse_commit(commit))
+				die("Invalid commit %s in submodule path %s",
+				    sha1_to_hex(entry.sha1), path.buf);
+
+			retval = read_tree_recursive(commit->tree,
+						     path.buf, path.len,
+						     stage, match, fn, context);
+			strbuf_release(&path);
+			if (retval)
+				return -1;
+			continue;
 		}
 	}
 	return 0;