# Check new commands' compatibility with old ones.
# Note, a command can be added to V1 at any time, it's ok if a
# new command has no corresponding old command.
old_commands = {}
for each file old_file in old_dir:
    old_idl := idl.parser.parse(old_file)
    if any commands in old_idl have non-empty api_version != "1":
        # We're not ready to handle future API versions yet.
        print error and quit

    for each command old_cmd in old_idl:
        if old_cmd.api_version == "":
            continue

        assert old_cmd.command_name not in old_commands
        old_commands.add(old_cmd.command_name)

        new_cmd := new_commands[old_cmd.command_name]
        assert new_cmd is not null # Can't remove a command from V1