Small issue with {X.tag} in MapCSS

[naoliv]

With the following test:

*[aeroway = aerodrome] ∈ *[aeroway = aerodrome] {
          throwWarning: tr("{0} inside {1}", "{1.tag}", "{0.tag}");
}

We can see a message like null inside aeroway=aerodrome when validating.

Is it possible to support the {X.tag} in examples like this?

JOSM

Revision: 8830
Repository Root: http://josm.openstreetmap.de/svn
Relative URL: ^/trunk
Last Changed Author: simon04
Last Changed Date: 2015-10-05 23:07:07 +0200 (Mon, 05 Oct 2015)
Build-Date: 2015-10-06 01:32:08
URL: http://josm.openstreetmap.de/svn/trunk
Repository UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last Changed Rev: 8830

Identification: JOSM/1.5 (8830 pt_BR) Linux Debian GNU/Linux testing (stretch)
Memory Usage: 927 MB / 9102 MB (708 MB allocated, but free)
Java version: 1.8.0_66-internal, Oracle Corporation, OpenJDK 64-Bit Server VM
VM arguments: [-Dawt.useSystemAAFontSettings=on]
Dataset consistency test: No problems found

[simon04]

{X.tag} is only evaluated for the right hand side of parent/child selectors. Counting X and the code just gets more complicated when taking both sides into account. I would rather not implement that in favour of simplicity. When the lefthand tag is needed, use the parent_tag() function, otherwise just specify the corresponding string.

[naoliv]

I was trying to avoid "duplicated" rules like this:

*[amenity = university] ∈ *[amenity = university],
*[amenity = university] ∈ *[amenity = college],
*[amenity = university] ∈ *[amenity = school] {
          throwWarning: tr("{0} dentro de {1}", "amenity=university", "{0.tag}");
}

*[amenity = college] ∈ *[amenity = college] {
          throwWarning: tr("{0} dentro de {1}", "amenity=college", "{0.tag}");
}

*[amenity = school] ∈ *[amenity = school] {
          throwWarning: tr("{0} dentro de {1}", "amenity=school", "{0.tag}");
}

*[aeroway = aerodrome] ∈ *[aeroway = aerodrome] {
          throwWarning: tr("{0} dentro de {1}", "aeroway=aerodrome", "{0.tag}");
}

*[aeroway = helipad] ∈ *[aeroway = helipad] {
          throwWarning: tr("{0} dentro de {1}", "aeroway=helipad", "{0.tag}");
}

I am unable to get what I want with parent_key(), but I guess it's broken: #11939 (or maybe I just don't know how to use it)