Ok, so there seems to be some controversy over whether we can really say that there are 'の-adjectives', or whether we simply use a noun in an "attributive" way (a term which I don't actually really understand). But it's clear that there's something interesting going on here, a deviation from the "default" understanding of の (as marking the genitive case), and I'd like some clarification.
Let's look at what seems to be for whatever the classical example:
○ 「永遠の愛」 "eternal love"
It's clear that we can't just apply the pattern "X の Y ⇔ Y of X" here*. But what is really going on? How do we know that the usual pattern doesn't apply here - is it contextual? A matter of set-phrasing? Is it because 永遠, being abstract, would need to be reified to be used in the normal way?
* It's worth noting that the pattern doesn't even hold in English here, which does seem to be a special case.
"love of eternity" - a strange thing to talk about, but in English, reification is implicit so this works just as well as "love of gold".
But what is more strange is that with "love" in particular, this doesn't have the normal genitive-case meaning - an English speaker parses "love of gold" not as the love which is expressed by gold, but love such that gold is the thing that is loved. Similarly for "eternity", following the same role.
And it doesn't even work the same way with similar words... * "desire/lust of gold" - should be "desire/lust for gold". But regardless, a love which is eternal is not the same thing as a love which is expressed by (belongs to, really; but in what other sense can love be possessed than by expressing it?) eternity-seen-as-an-entity, which would be the default interpretation of the pattern.
What happens in Japanese with that example? 「金の愛」 - grammatical? How would it be interpreted? How about with explicit reification (「金のことの愛」・「金のものの愛」）？
And how literal is it to translate 「永遠の」 as "eternal"? Can we describe what's going on here more pedantically? What determines our ability to use a noun this way with の?
And am I getting too philosophical? :)