I would personally prefer it being just 100% like assigning the player to somebody that just keeps skipping everything it can skip and clicks randomly on anything it must do (but this would require fixing the placement phase itself as being a must do, preferably with a property to allow having the current free-not-to-place behaviour for custom maps).

What you seem to be describing is essentially set players to default to DNAI and using isHidden=true.

In essence, pretty much, but instead of using a combination of flags and exposing the implementation detail of DNAI, we create a primary attribute for it.

For example, Conquest, with a DNAI player, it should do the random placement of territory selection and place its units but otherwise not move. Let's say we wanted another player to be a neutral buffer that did not place. In such an example it would not place and would not have a turn. In this scenario you could replace the DNAI with another AI and it would still be a 1v1 if you play against it. But say you want to make it interesting with neutrals occupying part of the map, that could not be done. Hence potentially a "third player type" that is effectively a combination of DNAI, isHidden=true, and does not collect, spend, nor place units (and is in effect, a neutral)

Also "Neutral" is a very bad name even for NWO and such, since we also have the relationship archetype "Neutral", that means the player is actually "Neutral", while the "Neutral" player itself is not "Neutral" at all, but always "Enemy" to everyone (that would be the archetype "War", not "Neutral", for relationships and politics). There is really nothing "Neutral" about the "Neutral" NWO player: it is an "Enemy" (to everyone) player that never moves or attack.

This isn't the case for weak/fast/hard AI which are meant to be "intelligent" AI that try to do all the possible actions given to them and optimize their chance of "winning".

No, ProAI uses a separate casualty selection that is more advanced than Weak/DoesNothing: https://github.com/triplea-game/triplea/blob/master/game-core/src/main/java/games/strategy/triplea/ai/pro/AbstractProAi.java#L346

Right, this is the reason why I would prefer avoiding using "Hard" AI (thus I need "Does Nothing" AI, or something like that), especially since it can be changed any time in the future. I don't want this player to "think" about what to select, but just always go by the autoselect. For example, if, on the last round of a battle, you have a 2/1 and a 1/4 units left and the killed defenders hit once, a thinking player may decide to take out the 2/1 unit, while this non-thinking player should always take out the 1/4 one, instead.

But for your prospective map and perhaps any others, I do wonder, @Cernel why not use a true neutral player?

I tried to use the "Neutral" player, at first, but it didn't work, either because you cannot assign phases to it or because you cannot assign triggers to it or both (I don't exactly remember, as I opened this topic 2 months ago).

My opinion is that DNAI should behave like a neutral player.

From another perspective, IMO using AI to get the behavior of a neutral player is a bad way to go. Instead I think the right feature is to be able to mark players as neutral which would remove their player slots and avoids loads of confusion and frankly other hackery.

But for your prospective map and perhaps any others, I do wonder, @Cernel why not use a true neutral player?

Any cases where we really want a player to just mindless place units can be considered apart from AIs (for example, wouldn't triggers be able to accomplish that just fine?)

So, I thought I made this clear, but I'll further clarify that FOR THIS ONE GAME DNAI is not required to place anything, as all the placements is made by triggers. What DNAI should be doing in this one is mindlessly attacking, resolving battles in a random order and taking casualties always by the autoselector (it has no retreat decisions, since the units are placed directly into the enemy territories).

As far as I'm concerned though AIs should not be a tool of map makers and maps should not be aware of AIs.

I think most map makers would disagree with this. Either I'm misunderstanding or just not seeing how you would handle the various maps that are defaulting players to AI and using hidden players.

Yeah, a brief definition should probably be added to POS2 XML

I would disagree, players want to know this information as well for what a given AI does. As far as I'm concerned though AIs should not be a tool of map makers and maps should not be aware of AIs. On the other hand selecting more players to be neutrals via another means would be the right feature. Any cases where we really want a player to just mindless place units can be considered apart from AIs (for example, wouldn't triggers be able to accomplish that just fine?)

@Cernel Sorry, I think I missed this thread. Yeah, a brief definition should probably be added to POS2 XML. Yes, "Neutral", DoesNothing, and Weak all use the same casualty selection which is default plus interleaving carriers and planes. Once the current PR that is potentially altering this is decided on then an update would be good.

@redrum Are you sure it's not actually weak AI that neutral player uses? Is it indeterminate and based on the location of code?

For example, in casualtySelector.java:

    final Player tripleaPlayer =
        player.isNull() ? new WeakAi(player.getName()) : bridge.getRemotePlayer(player);

From what I can tell DNAI is weak AI that does not move. Weak AI shares the same casualty selection as ProAI where it uses default casualty with interleaved carriers+figs.

I guess what @redrum means is that the "Neutral" player is using Weak AI too?

@Cernel The "Neutral" (null) player uses the same casualty selection as "DoesNothing" which is essentially the default plus interleaving carriers and planes.

Good to know, this is exactly what I wanted and what I actually went with, since nobody answered me 2 months ago.

I would recommend using this for any player that is just taking part in battles and not meant to move/purchase/etc.

Also for players (like this one) having "Conduct Combat" phases and attacking during the same? If positive, can we document this as intended and "stable" somewhere?

For example, in casualtySelector.java:

    final Player tripleaPlayer =
        player.isNull() ? new WeakAi(player.getName()) : bridge.getRemotePlayer(player);

From what I can tell DNAI is weak AI that does not move. Weak AI shares the same casualty selection as ProAI where it uses default casualty with interleaved carriers+figs.