init

    pub fn init(wip: *Wip, gpa: Allocator) !void {
        wip.* = .{
            .gpa = gpa,
            .string_bytes = .empty,
            .extra = .empty,
            .root_list = .empty,
        };

        // So that 0 can be used to indicate a null string.
        try wip.string_bytes.append(gpa, 0);

        assert(0 == try addExtra(wip, ErrorMessageList{
            .len = 0,
            .start = 0,
            .compile_log_text = 0,
        }));
    }