[Shadow]: @host rules defined within @media selectors are not applied

[Steve Orvell]

Created attachment 190076 [details]
reduction

With a construction like this, an @host rule is not applied.

@media screen and (max-width: 800px) {
   @host {
     * {
       background: green;
     }
   }
}

See the attached reduction and resize the window > and < 800px width to observe results.

[Takashi Sakamoto]

Currently CSSGrammar.y.in cannot parse @host in @media. So we need to modify CSSGrammar.y.in (maybe, adding host to block_valid_rule).

However if we change the place of @host with @media's (I'm not sure whether this is a valid css code or not), i.e.

@host {
   @media screen and (max-width: 800px) {
      * {
         background: green;
      }
   }
}

we need to change RuleSet.cpp (i.e. RuleSet::addChildRules).

[Dimitri Glazkov (Google)]

Tab, can you chime in on what's valid syntax or not?

[Dominic Cooney]

We are seeking clarification from the spec: <https://www.w3.org/Bugs/Public/show_bug.cgi?id=21242>

Given a lawyerly reading of that, @host rules should not be parsed in a stylesheet at all because the 'host' production, though defined, is not used in the 'stylesheet' production.

[Ryosuke Niwa]

@host isn't a thing anymore.