fix: access policy parsing

[tbrezot]

Simplify parsing code and correct parsing errors. Notice that now, empty access policies can be parsed. Parsing should be more efficient too, but we lack benchmarks for that.

The only downside is that allowing '&' or '|' inside attributes is painful to write. I consider it an acceptable limitation to the expressivness allowed by the parsing operation.

This is a breaking change though. All "Department::R&D" attributes have been renamed into "Department::RD".

[ackRow]

Nice refacto!
Maybe we should completely remove the attribute R&D/RD from our examples and tests if we decide to reserve the character &

[tbrezot]

Nice refacto! Maybe we should completely remove the attribute R&D/RD from our examples and tests if we decide to reserve the character &

Thanks. I pushed some commits to fix the issue with operator precedence (which was still not correctly applied). Now && can be implicit. I don't know if this is a feature we want to keep. I can add a test if we don't.

About R&D, I think it is OK to keep RD. I have heavily documented the parsing operation so users should not get mislead.

[tbrezot]

Also, we can add a parsing rule to parse dimensions which component is not specified into all the disjonction of all its components. For example:

"D1 && D2::A" -> "(D1::A || ... || D1:::L) && D2::A" (provided components from "D1" are "A" ... "L").

It seems pretty natural, does not require much work to implement and seems to fit nicely into the key derivation process. I will give it some more thoughts, but for now I am in favor of adding this feature.

[tbrezot]

After reading the code again, it may be more work than I thought. I propose we marge as-is.