cangen: architecture & function responsibility

[BlakeFreer]

Some things I don't like about the current architecture:

• the if sig.byte_order block in _get_masks_shifts() is pretty repetitive. We're really just mapping a byte order string to a function. This can be more direct with a dictionary with string keys and function values. the current code is more obvious, don't change this
  • cantools also guarantees that the byteorder is valid so we don't need an explicit check
• we create the Jinja environment multiple times (twice per bus). This should be abstracted out and only run once. Maybe it gets made in generate_can_from_dbc and passed into generate_code? Would be nice to have a function that creates and returns the environment with all filters set
• after the last bullet, is there still value in the generate_from_jinja_template function? Should it be inlined into generate_code? It's a bit of a strange function given how many parameters it requires and how little it does. Maybe the two calls to this function could be replaced by a loop over (CAN_MESSAGES_TEMPLATE_FILENAME, MSG_REGISTRY_TEMPLATE_FILENAME)or something simila
• i'm not a huge fan of variables/ return types that look like Dict[str, Dict[str, Tuple[List[int], List[int]]]]: This is really hard to understand. We should at least use dataclasses to bundle some of this information into a named type.
• Log levels: since cangen can be used standalone, we shouldn't require the user to know cmake logging levels to use it. We should have two mutually exclusive arguments: a --verbose aka -v flag and --cmake-log-level=### option, the latter of which replaces the current --log-level. The parse() function should figure out which was passed and convert that to a python logging level. You can then set args.loglevel to this value and directly pass args.level to `logger.setLevel
  • this will require you to store and manipulate the value from parser.parse_args() before returning it
• the current functions names aren't great. Renaming them may also help decide how to organize the behaviour
  • if you rename the cangen entry point, make sure to update pyproject.toml.