[PATCH 2/3 v2'] xserver: Introduce negated conditions in Match patterns

[Oleh R. Nykyforchyn]

On Fri, 17 Jun 2011 08:44:58 -0700
Dan Nicholson <dbn.lists at gmail.com> wrote:

> This is really confusing. I think it says that if the pattern didn't
> match the attribute and the pattern was preceded by !, then we keep
> going even though it successfully matched what we asked for.
Yes, "!pattern" is a necessary, not a sufficient condition.

> Is this
> the "last pattern" thing?
Last "!pattern" is sufficient. This exception allows us to treat
    MatchProduct "!Mouse"
as "all but mice". 

> Why don't we break when match = TRUE?
> Assuming I've understood this correctly, I think it breaks how the
> current match rules are supposed to work.
It contradicts to treating of "|" as "or". The only existing rule (if it can be called a rule)
is "any match is sufficient".
> 
> MatchProduct "foo|bar"
> If the product name matches "foo" or "bar", use the class.
> 
> MatchProduct "foo"
> MatchProduct "bar"
> If the product name matches "foo" and "bar", use the class.
Correct
> 
> Following that logic, I would expect this:
> 
> MatchProduct "!foo|!bar"
> If the product name does not match "foo" or does not match "bar", use the class.
No, and this is one of reasons why I suggest
      MatchProduct "!foo" "!bar"
Here '|' is just a token separator, not logical "or". Hence the former is equivalent to 
> MatchProduct "!foo"
> MatchProduct "!bar"
> If the product name does not match "foo" and does not match "bar", use
> the class.

> I think you're trying to make the former act like the latter because
> that's what you'd typically want to do with negated conditions.
Yes

> Rather
> than making the code goofy, I'd rather have people use the correct
> logic. I think it could be really simple:
It is really simple, but less useful. I suggest "!foo" to filter out all attributes with
"foo" except those that were accepted before.  Thus we can demand
    MatchProduct "good|!goo"
and get "only good of all goo". If "|" is "or", this is impossible.
> 
> --
Oleh