archive: complain about path specs that don't match anything

Verify that all path specs match at least one path in the specified
tree and reject those that don't.

This would have made the bug fixed by 782a000 easier to find.

This implementation is simple to the point of being stupid.  It walks
the full tree for each path spec until it matches something.  It's short
and seems to be fast enough, though.

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

archive.c

@@ -211,10 +211,33 @@ static const struct archiver *lookup_archiver(const char *name)
 	return NULL;
 }
 
+static int reject_entry(const unsigned char *sha1, const char *base,
+			int baselen, const char *filename, unsigned mode,
+			int stage, void *context)
+{
+	return -1;
+}
+
+static int path_exists(struct tree *tree, const char *path)
+{
+	const char *pathspec[] = { path, NULL };
+
+	if (read_tree_recursive(tree, "", 0, 0, pathspec, reject_entry, NULL))
+		return 1;
+	return 0;
+}
+
 static void parse_pathspec_arg(const char **pathspec,
 		struct archiver_args *ar_args)
 {
-	ar_args->pathspec = get_pathspec("", pathspec);
+	ar_args->pathspec = pathspec = get_pathspec("", pathspec);
+	if (pathspec) {
+		while (*pathspec) {
+			if (!path_exists(ar_args->tree, *pathspec))
+				die("path not found: %s", *pathspec);
+			pathspec++;
+		}
+	}
 }
 
 static void parse_treeish_arg(const char **argv,