addBundleAsRoots

    pub fn addBundleAsRoots(wip: *Wip, other: ErrorBundle) !void {
        const gpa = wip.gpa;

        try wip.string_bytes.ensureUnusedCapacity(gpa, other.string_bytes.len);
        try wip.extra.ensureUnusedCapacity(gpa, other.extra.len);

        const other_list = other.getMessages();

        try wip.root_list.ensureUnusedCapacity(gpa, other_list.len);
        for (other_list) |other_msg| {
            // The ensureUnusedCapacity calls above guarantees this.
            wip.root_list.appendAssumeCapacity(wip.addOtherMessage(other, other_msg) catch unreachable);
        }
    }