Unable to parse & lines

[alistair23]

zcbor is unable to parse the & (choice) operator

For example when running

zcbor code --cddl ./test.cddl -t spdm-toc --encode --output-c out.c --output-h out.h

on:

$version-scheme /= decimal

version-map = {
  &(version: 0) => text
  ? &(version-scheme: 1) => $version-scheme
}

The following exception occurs

Parsing files: ./test.cddl, .local/lib/python3.10/site-packages/zcbor/cddl/prelude.cddl
Traceback (most recent call last):
  File ".local/lib/python3.10/site-packages/zcbor/zcbor.py", line 847, in get_value
    handler(match_str)
  File ".local/lib/python3.10/site-packages/zcbor/zcbor.py", line 724, in <lambda>
    lambda map_str: self.type_and_value("MAP", lambda: self.parse(map_str))),
  File ".local/lib/python3.10/site-packages/zcbor/zcbor.py", line 490, in type_and_value
    self.set_value(value_generator)
  File ".local/lib/python3.10/site-packages/zcbor/zcbor.py", line 493, in set_value
    value = value_generator()
  File ".local/lib/python3.10/site-packages/zcbor/zcbor.py", line 724, in <lambda>
    lambda map_str: self.type_and_value("MAP", lambda: self.parse(map_str))),
  File ".local/lib/python3.10/site-packages/zcbor/zcbor.py", line 934, in parse
    instr = value.get_value(instr)
  File ".local/lib/python3.10/site-packages/zcbor/zcbor.py", line 858, in get_value
    raise TypeError("Could not parse this: '%s'" % instr)
TypeError: Could not parse this: '&(version: 0) => text   ? &(version-scheme: 1) => $version-scheme'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File ".local/bin/zcbor", line 8, in <module>
    sys.exit(main())
  File ".local/lib/python3.10/site-packages/zcbor/zcbor.py", line 3081, in main
    args.process(args)
  File ".local/lib/python3.10/site-packages/zcbor/zcbor.py", line 2940, in process_code
    cddl_res[mode] = CodeGenerator.from_cddl(
  File ".local/lib/python3.10/site-packages/zcbor/zcbor.py", line 1699, in from_cddl
    cddl_res = super(CodeGenerator, cddl_class).from_cddl(*args, **kwargs)
  File ".local/lib/python3.10/site-packages/zcbor/zcbor.py", line 269, in from_cddl
    parsed.get_value(cddl_string.replace("\n", " ").lstrip("&"))
  File ".local/lib/python3.10/site-packages/zcbor/zcbor.py", line 849, in get_value
    raise Exception("Failed while parsing this: '%s'" % match_str) from e
Exception: Failed while parsing this: '   &(version: 0) => text   ? &(version-scheme: 1) => $version-scheme '

[oyvindronningstad]

Thanks for the report. This is not supported, and there are currently no plans to support it, since AFAIU you can acheive the same thing quite easily with '/'. I will track this internally though.

[nslowell]

As the RFC hints at in 2.2.2.2., there is value in this feature in the situation where many values are given semantic names in a group but then someone has a desire to create a choice. It would be much more tedious to accumulate the names into a choice using '/' than just simply using the group that already exists and using '&'.

[sam-golioth]

This tripped me up today as well. I find that the & operator makes the CDDL more readable and maintainable, and would very much appreciate support being added into zcbor.