Russia is not a US ally, but Russia is an ally of Syria (and Russia has explicitly stated THEY would retaliate if the US attacked Syria, so along with treason its more proof of trump's collusion with Russia). It would be like North Korea calling Britain to tell say they were about to attack the US. Informing the enemy's ally, who is also a hostile foreign power not our ally, is the same as directly informing the target. Not even arguing semantics and technicalities will work here.
I think a better analogy would be North Korea warning the US before it launched an attack on a South Korean base, in the case of the Syria strike and the hypothetical I just mentioned it is in the attacking states interest to try and mitigate the possibility of conflict with a nuclear power. I don't know what North Korea could possibly hope to gain out of warning the UK about an imminent attack on the US...
I don't see how the Trump administrations performance of an action which is contrary to Russia's interests and expressed desires is supposed to function as evidence of "trump's [sic] collusion with Russia", assuming that you are referring to the election scandal and not this isolated incident. I am interpreting you as referring to the former because it would be tautological to suggest an event functioned as proof of itself.
by law if you attack a county's ally you're attacking both (or rather, every allied) countries.
It depends what you mean by ally. I am under the impression that this is only true if the countries have a mutual defense treaty which places signatories under an obligation to intervene in the event of an attack. As far as I know there is no treaty of this nature between Russia and Syria, which is not to say that one doesn't exist. For the record I am aware that Syria and Russia are signatories to numerous bilateral and multilateral treaties, some of which stipulate some level of military cooperation between the two countries. However, "military cooperation" is fairly vague, and what is less clear is whether Russia is bound by some treaty to intervene militarily on behalf of Syria in circumstances like the ones which transpired last week.
Don't get me wrong, I don't actually support this strike. Much as I dislike Assad, I am not sure that I see a way towards peace in Syria which doesn't involve Assad retaining some degree of political control. There are just too many factions with completely different geopolitical goals, none of which have any experience governing a country so far as I am aware. I don't see how removing Assad really improves the prospect of having a functioning government, which is necessary to roll back ISIS and try to get the country back on its feet.
Despite my opposition to this strike, I have a hard time understanding how anybody could honestly believe it was treasonous for the president of the US to take steps to avoid conflict with the state who owns the second largest nuclear arsenal on earth. Moreover, it seems to me that one must be engaged in mental gymnastics to suppose that the performance of an action which undermined Russia's regional interests provides support for the conclusion that Trump has engaged in longer-term collusion with Russia. I don't have much of an opinion on the extent to which the Trump administration is guilty of cooperating with Russia because I don't know enough about it, I certainly think its possible they have cooperated with regard to the US election; however, I feel the recent strike against Syria would have to count as (far from conclusive) evidence against this alleged cooperation.
But warning Russia would have informed the Syrians if Russians suddenly fled the base. Tactically, its pretty weird.
It isn't that weird tactically, if you assume that part of the US tactics were to avoid conflict with Russia then it isn't weird at all. Sometimes tactical goals can be in tension with one another and a compromise needs to be made. In my view, the strike was more symbolic than anything, it was Trump signalling to regional allies and enemies alike that the US is willing to use military force if an enemy state flagrantly violates international law. I don't think disabling the base was of particular concern, my understanding is that the Assad regime has over 20 other military airbases in Syria, so whether Shayrat Airbase can function or not is fairly inconsequential.