[#1292] Explicitly state that table entries declared with 'const entries' cannot be assigned numeric priorities

[kfcripps]

Closes #1292 and closes p4lang/p4c#4792.

As mentioned in p4lang/p4c#4792, p4c does not support the priority keyword for entries of a table that has const entries.

Feel free to suggest better wording or a better place for this addition.

[kfcripps]

I cannot request reviews in this repository, so instead I am tagging @jafingerhut @vlstill @ChrisDodd

[jafingerhut]

Looks good to me.

[jafingerhut]

@kfcripps Can you edit your original comment on this PR to mention that p4c's implementation does not support explicitly specifying priority values within const entries? (assuming I am recalling that correctly). I am not certain, but I believe that p4c never supported explicit priorities in this case, because when explicit priority support was added, it was done only for entries without const.

That is the kind of supporting detail that can help when/if this comes up in discussion in the language design work group.

[kfcripps]

@kfcripps Can you edit your original comment on this PR to mention that p4c's implementation does not support explicitly specifying priority values within const entries? (assuming I am recalling that correctly). I am not certain, but I believe that p4c never supported explicit priorities in this case, because when explicit priority support was added, it was done only for entries without const.

That is the kind of supporting detail that can help when/if this comes up in discussion in the language design work group.

Done. I don't know if p4c never supported explicit priorities for entries of tables with const entries, but it did not support this as of when I opened p4lang/p4c#4792.

I cannot merge this so feel free to merge if you are all happy with the changes.

[jafingerhut]

Added ldwg-discussion label to this issue, to remind us to talk about it at the next LDWG meeting in February, if it has not been merged before then.