[cifs-protocol] [MS-DTYP] Conditional ACE SDDL: NOT syntax clarification.

[Douglas Bagnall]

hi Dochelp,

In the ABNF for SDDL, in 2.5.1.1, the only place the NOT operator "!" is 
mentioned is in the cond-expr line:

       cond-expr = term /                                              \
                   term [wspace] ("||" / "&&" ) [wspace] cond-expr /   \
                   (["!"] [wspace] "(" cond-expr ")")


(We have already established in 2302020040006024 / 
https://lists.samba.org/archive/cifs-protocol/2023-February/003947.html that the 
second part with the "||" or "&&" is erroneous -- this question is about the 
third part, with the '["!"]').

So that says the only place a "!" can occur is in front of a parenthetical 
expression; you can't write "!A", you need to say "!(A)".

That would be OK, and I have been working on that basis, but then in 2.5.1.3 
"Parentheses and Order of Precedence", the "!" operator is given a middling 
precedence, below that of e.g. "==". And that makes me wonder about an 
expression like

    !(A) == B

Since == has higher precedence than !, it will grab the (A) before the ! can, 
and the expression is effectively "!(A == B)"; if you mean to do it the other 
way, you need to write "(!(A)) == B". But that looks silly. It makes me doubt 
that the semantic meaning is so divorced from the syntactic rule, and leads me 
to think the ABNF is taking another descriptive short cut.

Does '!' really always need to be followed by '('?

cheers,
Douglas