Actions

An action is something a player can do to achieve something in the game. It has properties like cost, chance of success and effects. Some of those properties are configurable using effects and other ruleset settings. To learn how to change them read Effects and the rule set files of classic. An action enabler allows a player to do an action.

Generalized Action Enablers

Some actions have generalized action enablers. An action like that can have zero, one or more action enablers defined for it in the ruleset. The player can do the action only when at least one generalized action enabler says that the action is enabled (and all its hard requirements are fulfilled). A ruleset author can therefore disable an action by not defining any action enablers for it in his ruleset.

A generalized action enabler lives in game.ruleset. It consists of the action it enables and two requirement vectors. The first requirement vector, actor_reqs, applies to the entity doing the action. The second, target_reqs, applies to its target. If both requirement vectors are fulfilled the action is enabled as far as the action enabler is concerned. Note that an action’s hard requirements still may make it impossible.

In some situations an action controlled by generalized action enablers may be impossible because of limitations in Freeciv21 itself. Those limitations are called hard requirements. The hard requirements of each action are documented below in the section Actions and Their Hard Requirements.

If the player does not have the knowledge required to find out if an action is enabled or not the action is shown to the player in case it is possible. The game will indicate the uncertainty to the player.

Should the player order a unit to do an illegal action the server will inform the player that his unit was unable to perform the action. The actor unit may also lose a ruleset configurable amount of move fragments.

Example:

[actionenabler_veil_the_threat_of_terror]
action = "Incite City"
actor_reqs    =
    { "type",    "name",                 "range", "present"
      "DiplRel", "Has Casus Belli",      "Local", TRUE
      "DiplRel", "Provided Casus Belli", "Local", FALSE
      "DiplRel", "Is foreign",           "Local", TRUE
    }

Another Example:

[actionenabler_go_bind_your_sons_to_exile]
action = "Incite City"
actor_reqs    =
    { "type",    "name",       "range",  "present"
      "Tech",    "Flight",     "Player", TRUE
      "DiplRel", "Is foreign", "Local",  TRUE
    }
target_reqs    =
    { "type",   "name",    "range",  "present"
      "Tech",   "Writing", "Player", False
    }

Above are two action enablers. They both enable the action “Incite City”. If all the conditions of at least one of them are fulfilled it will be enabled. No information is given to the player about what action enabler enabled an action.

The first action enabler, actionenabler_veil_the_threat_of_terror, is simple. It allows a player to incite a city if he has a reason to declare war on its owner AND the city’s owner does not have a reason to declare war on him.

The second action enabler, actionenabler_go_bind_your_sons_to_exile, is more complex. It allows a player that has Flight to bribe the cities of civilizations that do not have Writing. The complexity is caused by the requirement that the target does not know Writing. If the civilization of the target city knows Writing or not may be unknown to the acting player. To avoid this complexity a requirement that the acting player has an embassy to the target cities civilization (and therefore knowledge about its techs) can be added.

Requirement Vector Rules

An action enabler has two requirement vectors that must be TRUE at the same time. This creates some corner cases you will not find with single requirement vectors. The rules below tries to deal with them.

A DiplRel requirement with the range Local should always be put in the actor requirements.

A local DiplRel requirement can always be expressed as an actor requirement.
Only having to care about local DiplRel requirements in the actor requirements allows the Freeciv21 code responsible for reasoning about action enablers to be simpler and faster.
If player A having a diplomatic relationship to player B implies that player B has the same relationship to player A the relationship is symmetric. Examples: Is foreign and War
Symmetric local DiplReal requirements can be moved directly from the target requirement vector to the actor requirement vector.
Asymmetric local DiplReal requirements must test for the same thing in the opposite direction. Example: Hosts embassy -> Has embassy

Actions and Lua

Right before an action is executed, but after it is known to be legal, a signal is emitted to Lua. It has access to the same information as the server. It obviously does not have access to the result of the action since it is not done yet.

The signal’s name starts with action_started_, then the actor kind, then another _ and in the end the target kind. The signal that is emitted when a unit performs an action on a city is therefore action_started_unit_city.

The signal has three parameters. The first parameter is the action that is about to get started. The second is the actor. The third parameter is the target. The parameters of action_started_unit_city is therefore action, actor_unit, and finally target city.

To get the rule name of an action, that is the name used in action enablers, you can use the method rule_name(). To get a translated name that is nice to show to players use name_translation().

Example 1: The following Lua code will log all actions done by any unit to a city, to another unit, to a unit stack, to a tile or to itself:

function action_started_callback(action, actor, target)
  local target_owner
  if target == nil then
    target_owner = "it self"
  elseif target.owner == nil then
    target_owner = "unowned"
  else
    target_owner = target.owner.nation:plural_translation()
  end

  log.normal(_("%d: %s (rule name: %s) performed by %s %s (id: %d) on %s"),
            game.current_turn(),
            action:name_translation(),
            action:rule_name(),
            actor.owner.nation:plural_translation(),
            actor.utype:rule_name(),
            actor.id,
            target_owner)
end

signal.connect("action_started_unit_city", "action_started_callback")
signal.connect("action_started_unit_unit", "action_started_callback")
signal.connect("action_started_unit_units", "action_started_callback")
signal.connect("action_started_unit_tile", "action_started_callback")
signal.connect("action_started_unit_self", "action_started_callback")

Example 2: The following Lua code will make a player that poisons the population of cities risk civil war:

function action_started_callback(action, actor, target)
  if action:rule_name() == "Poison City" then
    edit.civil_war(actor.owner, 5);
  end
end

signal.connect("action_started_unit_city", "action_started_callback")

Actions and Their Hard Requirements

Freeciv21 can only allow a player to perform an action when the action’s hard requirements are fulfilled. Some, but not all, hard requirements can be expressed in an action enabler. Putting them there makes it clearer what the rule actually is. Parts of Freeciv21 reasons about action enablers. Examples are self contradicting rule detection and the help system. Including the hard requirements rules in each enabler of its action is therefore obligatory for some hard requirements. Those hard requirements are marked with an exclamation mark (!).

Actions Done By A Unit Against A City

Establish Embassy

Establish a real embassy to the target player.

Rules:

UI name can be set using ui_name_establish_embassy.
actor must be aware that the target exists.
actor cannot have a real embassy to the target player. (!)
actor must be on the same tile as the target or on the tile next to it.
target must be foreign. (!)

Establish Embassy Stay

Establish a real embassy to the target player.

Rules:

UI name can be set using ui_name_establish_embassy.
spends the actor unit.
actor must be aware that the target exists.
actor cannot have a real embassy to the target player. (!)
actor must be on the same tile as the target or on the tile next to it.
target must be foreign. (!)

Investigate City

Look at the city dialog of a foreign city.

Rules:

UI name can be set using ui_name_investigate_city.
actor must be aware that the target exists.
actor must be on the same tile as the target or on the tile next to it.
target must be foreign. (!)

Investigate City Spend Unit

Look at the city dialog of a foreign city.

Rules:

UI name can be set using ui_name_investigate_city.
spends the actor unit.
actor must be aware that the target exists.
actor must be on the same tile as the target or on the tile next to it.
target must be foreign. (!)

Sabotage City

Destroy a building or the production in the target city.

Rules:

UI name can be set using ui_name_sabotage_city.
spends the actor unit.
actor must be aware that the target exists.
actor must be on the same tile as the target or on the tile next to it.

Sabotage City Escape

Destroy a building or the production in the target city.

Rules:

UI name can be set using ui_name_sabotage_city_escape.
actor must be aware that the target exists.
actor must be on the same tile as the target or on the tile next to it.

Targeted Sabotage City

Destroy a building in the target city.

Rules:

UI name can be set using ui_name_targeted_sabotage_city.
spends the actor unit.
actor must be aware that the target exists.
actor must be on the same tile as the target or on the tile next to it.

Targeted Sabotage City Escape

Destroy a building in the target city and escape.

Rules:

UI name can be set using ui_name_targeted_sabotage_city_escape.
actor must be aware that the target exists.
actor must be on the same tile as the target or on the tile next to it.

Sabotage City Production

Sabotage the city’s production.

Rules:

UI name can be set using ui_name_sabotage_city_production.
spends the actor unit.
actor must be aware that the target exists.
actor must be on the same tile as the target or on the tile next to it.

Sabotage City Production Escape

Sabotage the city’s production and escape.

Rules:

UI name can be set using ui_name_sabotage_city_production_escape.
actor must be aware that the target exists.
actor must be on the same tile as the target or on the tile next to it.

Poison City

Kill a citizen in the target city.

Rules:

UI name can be set using ui_name_poison_city.
spends the actor unit.
actor must be aware that the target exists.
actor must be on the same tile as the target or on the tile next to it.

Poison City Escape

Kill a citizen in the target city and escape.

Rules:

UI name can be set using ui_name_poison_city_escape.
actor must be aware that the target exists.
actor must be on the same tile as the target or on the tile next to it.

Spread Plague

Bio-terrorism. Infect the target city with an illness.

Rules:

UI name can be set using ui_name_spread_plague.
set if the actor unit is spent with spread_plague_actor_consuming_always.
may infect trade route connected cities if illness.illness_on is TRUE.
actor must be aware that the target exists.
actor must be on the same tile as the target or on the tile next to it.

Steal Tech

Steal a random tech from the target’s owner.

Rules:

UI name can be set using ui_name_steal_tech.
spends the actor unit.
will always fail when the tech theft is expected. Tech theft is expected when the number of previous tech thefts from the target city is above the limit set by the Stealings_Ignore effect.
actor must be aware that the target exists.
actor must be on the same tile as the target or on the tile next to it.
target must be foreign. (!)

Steal Tech Escape Expected

Steal a random tech from the target’s owner and escape.

Rules:

UI name can be set using ui_name_steal_tech_escape.
more likely to fail when the tech theft is expected. Tech theft is expected when the number of previous tech thefts from the target city is above the limit set by the Stealings_Ignore effect.
actor must be aware that the target exists.
actor must be on the same tile as the target or on the tile next to it.
target must be foreign. (!)

Targeted Steal Tech

Steal a specific tech from the targets owner.

Rules:

UI name can be set using ui_name_targeted_steal_tech.
spends the actor unit.
will always fail when the tech theft is expected. Tech theft is expected when the number of previous tech thefts from the target city is above the limit set by the Stealings_Ignore effect.
actor must be aware that the target exists.
actor must be on the same tile as the target or on the tile next to it.
target must be foreign. (!)

Targeted Steal Tech Escape Expected

Steal a specific tech from the targets owner and escape.

Rules:

UI name can be set using ui_name_targeted_steal_tech_escape.
more likely to fail when the tech theft is expected. Tech theft is expected when the number of previous tech thefts from the target city is above the limit set by the Stealings_Ignore effect.
actor must be aware that the target exists.
actor must be on the same tile as the target or on the tile next to it.
target must be foreign. (!)

Incite City

Pay the target city to join the actor owner’s side.

Rules:

UI name can be set using ui_name_incite_city.
spends the actor unit.
actor must be aware that the target exists.
actor must be on the same tile as the target or on the tile next to it.
target must be foreign. (!)

Incite City Escape

Pay the target city to join the actor owner’s side and escape.

Rules:

UI name can be set using ui_name_incite_city_escape.
actor must be aware that the target exists.
actor must be on the same tile as the target or on the tile next to it.
target must be foreign. (!)

Steal Gold

Steal some gold from the owner of the target city.

Rules:

UI name can be set using ui_name_steal_gold.
adjustable with the Max_Stolen_Gold_Pm effect and with the Thiefs_Share_Pm effect.
spends the actor unit.
actor must be aware that the target exists.
the targets owner must have more than 0 gold.
actor must be on the same tile as the target or on the tile next to it.
target must be foreign. (!)

Steal Gold Escape

Steal some gold from the owner of the target city and escape.

Rules:

UI name can be set using ui_name_steal_gold_escape.
adjustable with the Max_Stolen_Gold_Pm effect and with the Thiefs_Share_Pm effect.
actor must be aware that the target exists.
the targets owner must have more than 0 gold.
actor must be on the same tile as the target or on the tile next to it.
target must be foreign. (!)

Steal Maps

Steal parts of the owner of the target city’s map.

Rules:

UI name can be set using ui_name_steal_maps.
adjustable with the Maps_Stolen_Pct effect and the ruleset setting steal_maps_reveals_all_cities.
spends the actor unit.
actor must be aware that the target exists.
actor must be on the same tile as the target or on the tile next to it.
target must be foreign. (!)

Steal Maps Escape

Steal parts of the owner of the target city’s map and escape.

Rules:

UI name can be set using ui_name_steal_maps_escape.
adjustable with the Maps_Stolen_Pct effect and the ruleset setting steal_maps_reveals_all_cities.
actor must be aware that the target exists.
actor must be on the same tile as the target or on the tile next to it.
target must be foreign. (!)

Suitcase Nuke

Cause a nuclear explosion in the target city.

Rules:

UI name can be set using ui_name_suitcase_nuke.
spends the actor unit.
actor must be aware that the target exists.
actor must be on the same tile as the target or on the tile next to it.

Suitcase Nuke Escape

Cause a nuclear explosion in the target city and escape.

Rules:

UI name can be set using ui_name_suitcase_nuke_escape.
actor must be aware that the target exists.
actor must be on the same tile as the target or on the tile next to it.

Destroy City

Destroys the target city.

Rules:

UI name can be set using ui_name_destroy_city.
actor must be aware that the target exists.
actor must be on the same tile as the target or on the tile next to it.

Establish Trade Route

Establish a trade route to the target city.

Rules:

UI name can be set using ui_name_establish_trade_route.
actor must be aware that the target exists.
actor must be on the same tile as the target or on the tile next to it.
actor must have a home city. (!)
target must be foreign or trademindist tiles away from that home city.
trade route type pct (see “Trade settings”) cannot be 0%.
it is possible to establish a trade route between the cities as far as the two cities them self are concerned. Example: If one of the cities cannot have any trade routes at all it is impossible to establish a new one.

Enter Marketplace

Get a one time bonus without creating a trade route.

Rules:

UI name can be set using ui_name_enter_marketplace.
actor must be aware that the target exists.
if force_trade_route is TRUE “Establish Trade Route” must be impossible.
actor must be on the same tile as the target or on the tile next to it.
actor must have a home city. (!)
target must be foreign or trademindist tiles away from that home city.
trade route type (see Trade settings) cannot be 0%.

Help Wonder

Add the shields used to build the actor to the target city.

Rules:

UI name can be set using ui_name_help_wonder.
adjustable with the Unit_Shield_Value_Pct effect.
actor must be aware that the target exists.
actor must be on the same tile as the target unless help_wonder_max_range allows it to be further away. Default help_wonder_max_range is 1.
target city must need the extra shields to complete its production.

Recycle Unit

Add half the shields used to build the unit to target.

Rules:

UI name can be set using ui_name_recycle_unit.
adjustable with the Unit_Shield_Value_Pct effect.
actor must be aware that the target exists.
“Help Wonder” must be impossible.
actor must be on the same tile as the target unless recycle_unit_max_range allows it to be further away. Default recycle_unit_max_range is 1.
target city must need the extra shields to complete its production.

Join City

Add the actor to the target city’s population.

Rules:

UI name can be set using ui_name_join_city.
actor must be aware that the target exists.
actor must have population to add (set in pop_cost).
actor must be on the same tile as the target or on the tile next to it.
target city population must not become higher that the add_to_size_limit setting permits.
target must be able to grow to the size that adding the unit would result in.

Home City

Set target city as the actor unit’s new home city.

Rules:

UI name can be set using ui_name_home_city.
actor must be aware that the target exists.
actor must be on the same tile as the target.
actor must not have the NoHome unit type flag. (!)
cannot set existing home city as new home city.
target city has enough unused unit maintenance slots to support the actor unit. No problem if the actor unit spends 0 city slots.

Upgrade Unit

Upgrade the actor unit using the target’s facilities.

Rules:

UI name can be set using ui_name_upgrade_unit.
adjustable with the Unit_Shield_Value_Pct effect.
actor must be aware that the target exists.
actor must be on the same tile as the target.
actor player must have enough gold to pay for the upgrade.
actor unit must have a type to upgrade to (obsoleted_by).
actor unit’s upgraded form must be able to exist at its current location.
actor unit’s upgraded form must have room for its current cargo.
target player must be able to build the unit upgraded to.
target city must be domestic. (!)

Airlift Unit: Airlift actor unit to target city.

Rules:

UI name can be set using ui_name_airlift_unit.

max legal distance to the target can be set using airlift_max_range.

actor must be aware that the target exists.

the actor unit is not transporting another unit. (!)

the actor unit is not inside the target city.

the actor unit can exist in the target city (outside a transport).

the actor unit is in a city. (!)

the city the actor unit is in:

is domestic or, if airliftingstyle permits it, allied.

has Airlift (see the Airlift effect and the airliftingstyle setting).

the target city is domestic or, if airliftingstyle permits it, allied.

the target city has Airlift.

Nuke City

Detonate in the target city. Cause a nuclear explosion.

Rules:

UI name can be set using ui_name_nuke_city.
if force_capture_units is TRUE “Capture Units” must be impossible.
if force_bombard is TRUE “Bombard”, “Bombard 2”, and “Bombard 3” must be impossible.
the actor unit must be on a tile next to the target unless nuke_city_max_range allows it to be further away.

Conquer City

Conquer the target city.

Rules:

UI name can be set using ui_name_conquer_city.
actor must be aware that the target exists.
if force_capture_units is TRUE “Capture Units” must be impossible.
if force_bombard is TRUE “Bombard”, “Bombard 2”, and “Bombard 3” must be impossible.
if force_explode_nuclear is TRUE “Explode Nuclear”, “Nuke Units”, and “Nuke City” must be impossible.
“Attack” must be impossible.
the actor unit must be on a tile next to the target.
the actor player’s nation cannot be an animal barbarian. (!)
the actor unit’s current transport, if the actor unit is transported, must be in a city or in a base native to the current transport if the current transport’s unit class has the Unreachable unit class flag and the actor’s unit type does not list the current transport’s unit class in disembarks.
the actor unit does not have the CoastStrict unit type flag or the target city is on or adjacent to a tile that does not have the UnsafeCoast terrain flag.
the actor unit cannot be diplomatically forbidden from entering the tile of the target city.
the actor unit has the CanOccupyCity unit class flag. (!)
the actor cannot have the NonMil unit type flag. (!)
the actor unit has at least one move fragment left. (!)
the actor’s relationship to the target is War. (!)
actor unit must be able to exist outside of a transport at the target’s tile.
the target must be foreign. (!)
the target city contains 0 units. (!)

Conquer City 2

Conquer the target city.

Rules:

UI name can be set using ui_name_conquer_city_2.
A copy of “Conquer City”.
See “Conquer City” for everything else.

Surgical Strike Building

Destroy a specific building.

Rules:

UI name can be set using ui_name_surgical_strike_building.
actor must be aware that the target exists.
the actor unit must be on a tile next to the target.

Surgical Strike Production

Destroy the city production.

Rules:

UI name can be set using ui_name_surgical_strike_production.
actor must be aware that the target exists.
the actor unit must be on a tile next to the target.

Actions Done By A Unit Against Another Unit

Sabotage Unit

Halve the target unit’s hit points.

Rules:

UI name can be set using ui_name_sabotage_unit.
spends the actor unit.
actor must be on the same tile as the target or on the tile next to it.
target must be visible for the actor.

Sabotage Unit Escape

Halve the target unit’s hit points and escape.

Rules:

UI name can be set using ui_name_sabotage_unit_escape.
actor must be on the same tile as the target or on the tile next to it.
target must be visible for the actor.

Bribe Unit

Make the target unit join the actor owner’s side.

Rules:

UI name can be set using ui_name_bribe_unit.
actor must be on the same tile as the target or on the tile next to it.
target must be foreign. (!)
target must be visible for the actor.

Expel Unit

Expel the target unit to its owner’s capital.

Rules:

UI name can be set using ui_name_expel_unit.
actor must be on the same tile as the target or on the tile next to it.
target must be visible for the actor.
target’s owner must have a capital.

Heal Unit

Restore the target unit’s health.

Rules:

UI name can be set using ui_name_heal_unit.
actor must be on the same tile as the target or on the tile next to it.
target must be visible for the actor.

Transport Alight

Exit target transport to same tile.

Rules:

UI name can be set using ui_name_transport_alight.
actor must be on the same tile as the target.
actor must be transported. (!)
actor must be on a livable tile. (!)
target must be transporting. (!)
target must be in a city or in a native base if the target’s unit class has the Unreachable unit class flag and the actor’s unit type does not list the target’s unit class in disembarks.
target must be visible for the actor.

Transport Unload

Unload the target unit to same tile.

Rules:

UI name can be set using ui_name_transport_unload.
actor must be on the same tile as the target.
actor must have a transport_cap greater than 0.
actor must be transporting. (!)
actor must be in a city or in a native base if the actor’s unit class has the Unreachable unit class flag and the target’s unit type does not list the actor’s unit class in disembarks.
target must be transported. (!)
target must be on a livable tile. (!)
target must be visible for the actor.

Transport Board

Enter target transport on the same tile.

Rules:

UI name can be set using ui_name_transport_board.
the actor unit cannot currently be transported by the target unit.
the actor unit’s current transport, if the actor unit is transported, must be in a city or in a base native to the current transport if the current transport’s unit class has the Unreachable unit class flag and the actor’s unit type does not list the current transport’s unit class in the disembarks field.
the actor’s unit class must appear in the target unit type’s cargo field.
the actor unit unit type must be different from the target unit type.
the actor unit or its (recursive) cargo, if it has cargo, must be unable to transport itself, the target unit or the target unit’s transporters. See unit_transport_check().
boarding will not cause a situation with more than 5 recursive transports.
the target unit must be domestic, allied or on the same team as the actor unit is. (!)
target must be in a city or in a base native to it if the target’s unit class has the Unreachable unit class flag and the actor’s unit type does not list the target’s unit class in the embarks field.
the target must be transporting fewer units than its unit type’s transport_cap field.
target must be visible to the actor.

Transport Embark

Enter target transport on a different tile.

Rules:

UI name can be set using ui_name_transport_embark.
the actor unit must be on a tile next to the target.
the actor unit has at least one move fragment left. (!)
the actor unit cannot currently be transported by the target unit.
the actor unit’s current transport, if the actor unit is transported, must be in a city or in a base native to the current transport if the current transport’s unit class has the Unreachable unit class flag and the actor’s unit type does not list the current transport’s unit class in the disembarks field.
the actor unit’s type must be the target tile’s terrain animal if the player’s nation is an animal barbarian.
the actor unit cannot be diplomatically forbidden from entering the target tile.
the actor unit does not have the CoastStrict unit type flag or the target city is on or adjacent to a tile that does not have the UnsafeCoast terrain flag.
actor unit must be able to move to the target tile.
the actor’s unit class must appear in the target unit type’s cargo field.
the actor unit unit type must be different from the target unit type.
the actor unit or its (recursive) cargo, if it has cargo, must be unable to transport itself, the target unit or the target unit’s transporters. See unit_transport_check().
boarding will not cause a situation with more than 5 recursive transports.
the target unit must be domestic, allied, or on the same team as the actor unit is. (!)
target must be in a city or in a base native to it if the target’s unit class has the Unreachable unit class flag and the actor’s unit type does not list the target’s unit class in the embarks field.
the target must be transporting fewer units than its unit type’s transport_cap field.
the target tile cannot contain any city or units not allied to the actor unit and all its cargo.
target must be visible to the actor.

Actions Done By A Unit Against All Units At A Tile

Capture Units

Steal the target units.

Rules:

UI name can be set using ui_name_capture_units.
actor must be on a tile next to the target.
target must be foreign. (!)
target cannot be transporting other units. (!)

Bombard

Bombard the units (and city) at the tile without killing them.

Rules:

UI name can be set using ui_name_bombard.
if force_capture_units is TRUE, “Capture Units” must be impossible.
actor must have a bombard_rate > 0.
actor must have an attack > 0.
actor must be on a tile next to the target or, if bombard_max_range allows it, further away.
target cannot be in a city the actor player is not at war with.
target owner must be at war with actor. (!)

Bombard 2

Bombard the units (and city) at the tile without killing them.

Rules:

UI name can be set using ui_name_bombard_2.
actor must be on a tile next to the target or, if bombard_2_max_range allows it, further away.
A copy of “Bombard”.
See “Bombard” for everything else.

Bombard 3

Bombard the units (and city) at the tile without killing them.

Rules:

UI name can be set using ui_name_bombard_3.
actor must be on a tile next to the target or, if bombard_3_max_range allows it, further away.
A copy of “Bombard”.
See “Bombard” for everything else.

Attack

Attack an enemy unit, possibly survive.

Rules:

UI name can be set using ui_name_attack.
if force_capture_units is TRUE, “Capture Units” must be impossible.
if force_bombard is TRUE, “Bombard”, “Bombard 2”, and “Bombard 3” must be impossible.
if force_explode_nuclear is TRUE, “Explode Nuclear”, “Nuke Units”, and “Nuke City” must be impossible.
the actor must be on the tile next to the target.
the actor’s attack must be above 0.
the actor cannot have the NonMil unit type flag. (!)
the actor must be native to the target tile unless it has the AttackNonNative unit class flag and not the Only_Native_Attack unit type flag.
the target tile has no non enemy units. (!)
the target tile has no non enemy city.
one or all (unreachable protects) non transported units at the target tile must be reachable. A unit is reachable if any of the following is true:
- it does not have the Unreachable unit class flag.
- it is listed in the actor unit’s targets.
- it is in a city.
- it is on a tile with a native Extra.

Suicide Attack

Attack an enemy unit, die immediately.

Rules:

UI name can be set using ui_name_suicide_attack.
if force_capture_units is TRUE, “Capture Units” must be impossible.
if force_bombard is TRUE, “Bombard”, “Bombard 2”, and “Bombard 3” must be impossible.
if force_explode_nuclear is TRUE, “Explode Nuclear”, “Nuke Units”, and “Nuke City” must be impossible.
the actor must be on the tile next to the target.
the actor’s attack must be above 0.
the actor cannot have the NonMil unit type flag. (!)
the actor must be native to the target tile unless it has the AttackNonNative unit class flag and not the Only_Native_Attack unit type flag.
the target tile has no non enemy units. (!)
the target tile has no non enemy city.
one or all (unreachable protects) non transported units at the target tile must be reachable. A unit is reachable if any of the following is true:
- it does not have the Unreachable unit class flag.
- it is listed in the actor unit’s targets.
- it is in a city.
- it is on a tile with a native Extra.

Nuke Units

Detonate at the target unit stack. Cause a nuclear explosion.

Rules:

UI name can be set using ui_name_nuke_units.
if force_capture_units is TRUE, “Capture Units” must be impossible.
if force_bombard is TRUE, “Bombard”, “Bombard 2”, and “Bombard 3” must be impossible.
the actor unit must be on a tile next to the target unless nuke_units_max_range allows it to be further away.
one or all (unreachable protects) non transported units at the target tile must be reachable. A unit is reachable if any of the following is true:
- it does not have the Unreachable unit class flag.
- it is listed in the actor unit’s targets.
- it is in a city.
- it is on a tile with a native Extra.

Spy Attack

Trigger a diplomatic battle to eliminate tile defenders.

Rules:

UI name can be set using ui_name_spy_attack.
the actor must be on the tile next to the target.
the target tile must have at least 1 diplomatic defender.

Actions Done By A Unit Against A Tile

Found City

Found a city at the target tile.

Rules:

UI name can be set using ui_name_found_city.
city name must be legal.
the scenario setting prevent_new_cities must be false.
actor must be on the same tile as the target.
target must not have the NoCities terrain flag. (!)
target must not be closer than citymindist to nearest city.

Explode Nuclear

Detonate at the target tile. Cause a nuclear explosion.

Rules:

UI name can be set using ui_name_explode_nuclear.
if force_capture_units is TRUE, “Capture Units” must be impossible.
if force_bombard is TRUE, “Bombard”, “Bombard 2”, and “Bombard 3” must be impossible.
actor must be on the same tile as the target unless explode_nuclear_max_range allows it to be further away.

Paradrop Unit

Move the actor unit to the target tile.

Rules:

UI name can be set using ui_name_paradrop_unit.
can result in the conquest of the city at the target tile if:
- the actor player is not an animal barbarian.
- the actor unit has the CanOccupyCity unit class flag.
- the actor do not have the NonMil unit type flag.
- the actor’s relationship to the target is War.
- the target city contains 0 units.
the distance between actor and target is from 1 to paratroopers_range.
the actor unit has not paradropped this turn.
the actor unit is not transporting another unit. (!)
the actor unit cannot be diplomatically forbidden from entering the target tile. (!)
the target tile is known (does not have to be seen) by the actor.
if the target tile is seen:
- the actor unit must be able to exist outside a transport on the target tile. If the target tile does not have a visible transport the actor unit is able to load into on landing.
- the target tile cannot contain a city belonging to a player the actor has Peace, Cease-Fire, or Armistice with.
- the target tile cannot contain any seen unit belonging to a player the actor player has Peace, Cease-Fire, or Armistice with.

Transform Terrain

Transform tile terrain type.

Rules:

UI name can be set using ui_name_transform_terrain.
the actor unit has Settlers flag. (!)
terrain type must be one that can be transformed.

Cultivate

Transform tile terrain type by irrigating.

Rules:

UI name can be set using ui_name_cultivate_tf.
the actor unit has Settlers flag. (!)
terrain type must be one that can be transformed by irrigating.

Plant

Transform tile terrain type by planting.

Rules:

UI name can be set using ui_name_plant.
the actor unit has Settlers flag. (!)
terrain type must be one that can be transformed by mining.

Pillage

Pillage extra from tile.

Rules:

UI name can be set using ui_name_pillage.
terrain type must be one where pillaging is possible.
the target extra must be present at the target tile.
the terrain of the target tile must have a non zero pillage_time.
no other unit can be pillaging the target extra.
the target extra must have the Pillage removal cause.
the target extra’s rmreqs must be fulfilled.
the target extra cannot be a dependency of another extra present at the target tile.
the target extra cannot have the AlwaysOnCityCenter extra flag if the target tile has a city.
the target extra cannot have the AutoOnCityCenter extra flag if the target tile has a city and the city’s owner can rebuild it.
the target extra must be the rule chosen extra if the civstyle section’s pillage_select is FALSE.

Clean Pollution

Clean extra from the target tile.

Rules:

UI name can be set using ui_name_clean_pollution.
actor must be on the same tile as the target.
the actor unit has the Settlers unit type flag. (!)
the target extra must be present at the target tile.
the terrain of the target tile must have a non zero clean_pollution_time.
the target extra must have the CleanPollution removal cause.
the target extra’s rmreqs must be fulfilled.
the target extra cannot have the AlwaysOnCityCenter extra flag if the target tile has a city
the target extra cannot have the AutoOnCityCenter extra flag if the target tile has a city and the city’s owner can rebuild it.

Clean Fallout

Clean extra from the target tile.

Rules:

UI name can be set using ui_name_clean_fallout.
actor must be on the same tile as the target.
the actor unit has the Settlers unit type flag. (!)
the target extra must be present at the target tile.
the terrain of the target tile must have a non zero clean_fallout_time.
the target extra must have the CleanFallout removal cause.
the target extra’s rmreqs must be fulfilled.
the target extra cannot have the AlwaysOnCityCenter extra flag if the target tile has a city.
the target extra cannot have the AutoOnCityCenter extra flag if the target tile has a city and the city’s owner can rebuild it.

Build Road

Build road at the target tile.

Rules:

UI name can be set using ui_name_road.
actor must be on the same tile as the target.
the actor unit has the Settlers unit type flag. (!)
the target tile cannot have an extra that the target extra must bridge over (see extra type’s bridged_over value) unless the actor player knows a tech with the Bridge tech flag.
the target extra (the extra to be built) is a road.
the target tile does not already have the target extra.
the target extra is buildable (see extra type’s buildable value).
the target tile’s terrain’s road_time is not 0.
if the target extra is both a road and a base the target tile’s terrain’s base_time is not 0.
if the target extra is both a road and a base the target extra cannot claim land (see base type’s border_sq value) if the target tile has a city.
to begin a road the build requirements of the target road (see road type’s first_reqs value) must be fulfilled. Building a road when no (cardinal) adjacent tile has the target extra is considered beginning it.
the build requirements of the target extra (see extra type’s reqs value) must be fulfilled.

Build Base

Build base at the target tile.

Rules:

UI name can be set using ui_name_build_base.
the actor unit has the Settlers unit type flag. (!)
the target tile cannot have an extra that the target extra must bridge over (see extra type’s bridged_over value) unless the actor player knows a tech with the Bridge tech flag.
the target extra (the extra to be built) is a base.
the target tile does not already have the target extra.
the target extra is buildable (see extra type’s buildable value).
the target tile’s terrain’s base_time is not 0.
the target extra cannot claim land (see base type’s border_sq value) if the target tile has a city.
if the target extra is both a road and a base the target tile’s terrain’s road_time is not 0.
the build requirements of the target extra (see extra type’s reqs value) must be fulfilled.

Build Mine

Build mine at the target tile.

Rules:

UI name can be set using ui_name_build_mine.
actor must be on the same tile as the target.
the actor unit has the Settlers unit type flag. (!)
the target tile cannot have an extra that the target extra must bridge over (see extra type’s bridged_over value) unless the actor player knows a tech with the Bridge tech flag.
the target extra (the extra to be built) is a mine.
the target tile does not already have the target extra.
the target extra is buildable (see extra type’s buildable value).
the target tile’s terrain’s mining_time is not 0.
the target tile’s terrain’s mining_result is “yes”.
if the target extra is both a mine and a base the target tile’s terrain’s base_time is not 0.
if the target extra is both a mine and a base the target extra cannot claim land (see base type’s border_sq value) if the target tile has a city.
if the target extra is both a mine and a road the target tile’s terrain’s road_time is not 0.
the build requirements of the target extra (see extra type’s reqs value) must be fulfilled.

Build Irrigation

Build irrigation at the target tile.

Rules:

UI name can be set using ui_name_irrigate.
actor must be on the same tile as the target.
the actor unit has the Settlers unit type flag. (!)
the target tile cannot have an extra that the target extra must bridge over (see extra type’s bridged_over value) unless the actor player knows a tech with the Bridge tech flag.
the target extra (the extra to be built) is an irrigation.
the target tile does not already have the target extra.
the target extra is buildable (see extra type’s buildable value).
the target tile’s terrain’s irrigation_time is not 0.
the target tile’s terrain’s irrigation_result is “yes”.
if the target extra is both an irrigation and a base the target tile’s terrain’s base_time is not 0.
if the target extra is both an irrigation and a base the target extra cannot claim land (see base type’s border_sq value) if the target tile has a city.
if the target extra is both an irrigation and a road the target tile’s terrain’s road_time is not 0
the build requirements of the target extra (see extra type’s reqs value) must be fulfilled.

Transport Disembark

Exit transport to target tile.

Rules:

UI name can be set using ui_name_transport_disembark.
the actor unit must be on a tile next to the target.
the actor unit has at least one move fragment left. (!)
actor must be transported. (!)
the actor unit’s transport must be in a city or in a native base if the transport’s unit class has the Unreachable unit class flag and the actor’s unit type does not list the target’s unit class in disembarks.
the actor unit does not have the CoastStrict unit type flag or the target city is on or adjacent to a tile that does not have the UnsafeCoast terrain flag.
the actor unit cannot be diplomatically forbidden from entering the target tile.
the actor unit’s type must be the target tile’s terrain animal if the player’s nation is an animal barbarian.
actor unit must be able to exist outside of a transport at the target tile.
actor unit must be able to move to the target tile.
the target tile is not blocked for the actor unit by some other unit’s zone of control (ZOC)
the target tile cannot contain any city or units not allied to the actor unit and all its cargo.

Transport Disembark 2

Exit transport to target tile.

Rules:

UI name can be set using ui_name_transport_disembark_2.
A copy of “Transport Disembark”.
See “Transport Disembark” for everything else.

Actions Done By A Unit To It Self

Disband Unit

Disband the unit.

Rules:

spends the actor unit. Gives nothing in return. No shields spent to build the unit is added to the shield stock of any city even if the unit is located inside it.
UI name can be set using ui_name_disband_unit.
“Help Wonder” must be impossible.
“Recycle Unit” must be impossible.

Fortify

Fortify at tile.

Rules:

UI name can be set using ui_name_fortify.
the actor unit cannot already be fortified. (!)

Convert Unit

Convert the unit to another unit type.

Rules:

UI name can be set using ui_name_convert_unit.
actor unit must have a type to convert to (convert_to).
actor unit’s converted form must be able to exist at its current location.
actor unit’s converted form must have room for its current cargo.

Ruleset Defined Actions

User actions are “blank”. The ruleset does everything they do. The following ruleset variables allows user action number n to be further customized:

ui_name_user_action_n: The UI name shown to the user in the action selection dialog.
user_action_n_target_kind: The kind of target the action is done to. See target_reqs. Legal values: “individual cities”, “individual units”, “unit stacks”, “tiles”, or “itself”
user_action_n_min_range and user_action_n_max_range: What distance from the actor to the target is permitted for the action.
user_action_n_actor_consuming_always: TRUE if Freeciv21 should make sure that the actor is spent after the action is successfully done.

The current ruleset defined actions are “User Action 1”, “User Action 2”, and “User Action 3”.