[P1 Bug] Fix several Destiny Bond crashes (#4665)

* [P1 Bug] Fix several Destiny Bond crashes

* PR Feedback

src/data/move.ts

@@ -3834,8 +3834,8 @@ export class LastMoveDoublePowerAttr extends VariablePowerAttr {
 
     for (const p of pokemonActed) {
       const [ lastMove ] = p.getLastXMoves(1);
-      if (lastMove.result !== MoveResult.FAIL) {
+      if (lastMove?.result !== MoveResult.FAIL) {
-        if ((lastMove.result === MoveResult.SUCCESS) && (lastMove.move === this.move)) {
+        if ((lastMove?.result === MoveResult.SUCCESS) && (lastMove?.move === this.move)) {
           power.value *= 2;
           return true;
         } else {
@@ -4736,7 +4736,7 @@ export class AddBattlerTagAttr extends MoveEffectAttr {
   }
 
   canApply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean {
-    if (!super.canApply(user, target, move, args) || (this.cancelOnFail === true && user.getLastXMoves(1)[0].result === MoveResult.FAIL)) {
+    if (!super.canApply(user, target, move, args) || (this.cancelOnFail === true && user.getLastXMoves(1)[0]?.result === MoveResult.FAIL)) {
       return false;
     } else {
       return true;
@@ -5174,7 +5174,7 @@ export class AddArenaTagAttr extends MoveEffectAttr {
       return false;
     }
 
-    if ((move.chance < 0 || move.chance === 100 || user.randSeedInt(100) < move.chance) && user.getLastXMoves(1)[0].result === MoveResult.SUCCESS) {
+    if ((move.chance < 0 || move.chance === 100 || user.randSeedInt(100) < move.chance) && user.getLastXMoves(1)[0]?.result === MoveResult.SUCCESS) {
       user.scene.arena.addTag(this.tagType, this.turnCount, move.id, user.id, (this.selfSideTarget ? user : target).isPlayer() ? ArenaTagSide.PLAYER : ArenaTagSide.ENEMY);
       return true;
     }
@@ -5249,7 +5249,7 @@ export class AddArenaTrapTagHitAttr extends AddArenaTagAttr {
     const moveChance = this.getMoveChance(user, target, move, this.selfTarget, true);
     const side = (this.selfSideTarget ? user : target).isPlayer() ? ArenaTagSide.PLAYER : ArenaTagSide.ENEMY;
     const tag = user.scene.arena.getTagOnSide(this.tagType, side) as ArenaTrapTag;
-    if ((moveChance < 0 || moveChance === 100 || user.randSeedInt(100) < moveChance) && user.getLastXMoves(1)[0].result === MoveResult.SUCCESS) {
+    if ((moveChance < 0 || moveChance === 100 || user.randSeedInt(100) < moveChance) && user.getLastXMoves(1)[0]?.result === MoveResult.SUCCESS) {
       user.scene.arena.addTag(this.tagType, 0, move.id, user.id, side);
       if (!tag) {
         return true;
@@ -5386,7 +5386,7 @@ export class AddPledgeEffectAttr extends AddArenaTagAttr {
 
   override apply(user: Pokemon, target: Pokemon, move: Move, args: any[]): boolean {
     // TODO: add support for `HIT` effect triggering in AddArenaTagAttr to remove the need for this check
-    if (user.getLastXMoves(1)[0].result !== MoveResult.SUCCESS) {
+    if (user.getLastXMoves(1)[0]?.result !== MoveResult.SUCCESS) {
       return false;
     }
 

src/field/pokemon.ts

@@ -2810,15 +2810,16 @@ export default abstract class Pokemon extends Phaser.GameObjects.Container {
       if (this.isFainted()) {
         // set splice index here, so future scene queues happen before FaintedPhase
         this.scene.setPhaseQueueSplice();
+        if (!isNullOrUndefined(destinyTag) && dmg) {
+          // Destiny Bond will activate during FaintPhase
+          this.scene.unshiftPhase(new FaintPhase(this.scene, this.getBattlerIndex(), isOneHitKo, destinyTag, source));
+        } else {
           this.scene.unshiftPhase(new FaintPhase(this.scene, this.getBattlerIndex(), isOneHitKo));
+        }
         this.destroySubstitute();
         this.resetSummonData();
       }
 
-      if (dmg) {
-        destinyTag?.lapse(source, BattlerTagLapseType.CUSTOM);
-      }
-
       return result;
     }
   }

src/phases/faint-phase.ts

@@ -1,12 +1,12 @@
 import BattleScene from "#app/battle-scene";
 import { BattlerIndex, BattleType } from "#app/battle";
 import { applyPostFaintAbAttrs, PostFaintAbAttr, applyPostKnockOutAbAttrs, PostKnockOutAbAttr, applyPostVictoryAbAttrs, PostVictoryAbAttr } from "#app/data/ability";
-import { BattlerTagLapseType } from "#app/data/battler-tags";
+import { BattlerTagLapseType, DestinyBondTag } from "#app/data/battler-tags";
 import { battleSpecDialogue } from "#app/data/dialogue";
 import { allMoves, PostVictoryStatStageChangeAttr } from "#app/data/move";
 import { BattleSpec } from "#app/enums/battle-spec";
 import { StatusEffect } from "#app/enums/status-effect";
-import { PokemonMove, EnemyPokemon, PlayerPokemon, HitResult } from "#app/field/pokemon";
+import Pokemon, { PokemonMove, EnemyPokemon, PlayerPokemon, HitResult } from "#app/field/pokemon";
 import { getPokemonNameWithAffix } from "#app/messages";
 import { PokemonInstantReviveModifier } from "#app/modifier/modifier";
 import i18next from "i18next";
@@ -19,19 +19,39 @@ import { SwitchPhase } from "./switch-phase";
 import { VictoryPhase } from "./victory-phase";
 import { SpeciesFormChangeActiveTrigger } from "#app/data/pokemon-forms";
 import { SwitchType } from "#enums/switch-type";
+import { isNullOrUndefined } from "#app/utils";
 
 export class FaintPhase extends PokemonPhase {
+  /**
+   * Whether or not enduring (for this phase's purposes, Reviver Seed) should be prevented
+   */
   private preventEndure: boolean;
 
-  constructor(scene: BattleScene, battlerIndex: BattlerIndex, preventEndure?: boolean) {
+  /**
+   * Destiny Bond tag belonging to the currently fainting Pokemon, if applicable
+   */
+  private destinyTag?: DestinyBondTag;
+
+  /**
+   * The source Pokemon that dealt fatal damage and should get KO'd by Destiny Bond, if applicable
+   */
+  private source?: Pokemon;
+
+  constructor(scene: BattleScene, battlerIndex: BattlerIndex, preventEndure: boolean = false, destinyTag?: DestinyBondTag, source?: Pokemon) {
     super(scene, battlerIndex);
 
-    this.preventEndure = preventEndure!; // TODO: is this bang correct?
+    this.preventEndure = preventEndure;
+    this.destinyTag = destinyTag;
+    this.source = source;
   }
 
   start() {
     super.start();
 
+    if (!isNullOrUndefined(this.destinyTag) && !isNullOrUndefined(this.source)) {
+      this.destinyTag.lapse(this.source, BattlerTagLapseType.CUSTOM);
+    }
+
     if (!this.preventEndure) {
       const instantReviveModifier = this.scene.applyModifier(PokemonInstantReviveModifier, this.player, this.getPokemon()) as PokemonInstantReviveModifier;
 

src/test/moves/destiny_bond.test.ts

@@ -0,0 +1,255 @@
+import { ArenaTagSide, ArenaTrapTag } from "#app/data/arena-tag";
+import { allMoves } from "#app/data/move";
+import { Abilities } from "#enums/abilities";
+import { ArenaTagType } from "#enums/arena-tag-type";
+import { Moves } from "#enums/moves";
+import { Species } from "#enums/species";
+import GameManager from "#test/utils/gameManager";
+import Phaser from "phaser";
+import { afterEach, beforeAll, beforeEach, describe, expect, it, vi } from "vitest";
+import { BattlerIndex } from "#app/battle";
+import { StatusEffect } from "#enums/status-effect";
+import { PokemonInstantReviveModifier } from "#app/modifier/modifier";
+
+
+describe("Moves - Destiny Bond", () => {
+  let phaserGame: Phaser.Game;
+  let game: GameManager;
+
+  const defaultParty = [ Species.BULBASAUR, Species.SQUIRTLE ];
+  const enemyFirst = [ BattlerIndex.ENEMY, BattlerIndex.PLAYER ];
+  const playerFirst = [ BattlerIndex.PLAYER, BattlerIndex.ENEMY ];
+
+  beforeAll(() => {
+    phaserGame = new Phaser.Game({
+      type: Phaser.HEADLESS,
+    });
+  });
+
+  afterEach(() => {
+    game.phaseInterceptor.restoreOg();
+  });
+
+  beforeEach(() => {
+    game = new GameManager(phaserGame);
+    game.override.battleType("single")
+      .ability(Abilities.UNNERVE) // Pre-emptively prevent flakiness from opponent berries
+      .enemySpecies(Species.RATTATA)
+      .enemyAbility(Abilities.RUN_AWAY)
+      .startingLevel(100) // Make sure tested moves KO
+      .enemyLevel(5)
+      .enemyMoveset(Moves.DESTINY_BOND);
+  });
+
+  it("should KO the opponent on the same turn", async () => {
+    const moveToUse = Moves.TACKLE;
+
+    game.override.moveset(moveToUse);
+    await game.classicMode.startBattle(defaultParty);
+
+    const enemyPokemon = game.scene.getEnemyPokemon();
+    const playerPokemon = game.scene.getPlayerPokemon();
+
+    game.move.select(moveToUse);
+    await game.setTurnOrder(enemyFirst);
+    await game.phaseInterceptor.to("BerryPhase");
+
+    expect(enemyPokemon?.isFainted()).toBe(true);
+    expect(playerPokemon?.isFainted()).toBe(true);
+  });
+
+  it("should KO the opponent on the next turn", async () => {
+    const moveToUse = Moves.TACKLE;
+
+    game.override.moveset([ Moves.SPLASH, moveToUse ]);
+    await game.classicMode.startBattle(defaultParty);
+
+    const enemyPokemon = game.scene.getEnemyPokemon();
+    const playerPokemon = game.scene.getPlayerPokemon();
+
+    // Turn 1: Enemy uses Destiny Bond and doesn't faint
+    game.move.select(Moves.SPLASH);
+    await game.setTurnOrder(playerFirst);
+    await game.toNextTurn();
+
+    expect(enemyPokemon?.isFainted()).toBe(false);
+    expect(playerPokemon?.isFainted()).toBe(false);
+
+    // Turn 2: Player KO's the enemy before the enemy's turn
+    game.move.select(moveToUse);
+    await game.setTurnOrder(playerFirst);
+    await game.phaseInterceptor.to("BerryPhase");
+
+    expect(enemyPokemon?.isFainted()).toBe(true);
+    expect(playerPokemon?.isFainted()).toBe(true);
+  });
+
+  it("should fail if used twice in a row", async () => {
+    const moveToUse = Moves.TACKLE;
+
+    game.override.moveset([ Moves.SPLASH, moveToUse ]);
+    await game.classicMode.startBattle(defaultParty);
+
+    const enemyPokemon = game.scene.getEnemyPokemon();
+    const playerPokemon = game.scene.getPlayerPokemon();
+
+    // Turn 1: Enemy uses Destiny Bond and doesn't faint
+    game.move.select(Moves.SPLASH);
+    await game.setTurnOrder(enemyFirst);
+    await game.toNextTurn();
+
+    expect(enemyPokemon?.isFainted()).toBe(false);
+    expect(playerPokemon?.isFainted()).toBe(false);
+
+    // Turn 2: Enemy should fail Destiny Bond then get KO'd
+    game.move.select(moveToUse);
+    await game.setTurnOrder(enemyFirst);
+    await game.phaseInterceptor.to("BerryPhase");
+
+    expect(enemyPokemon?.isFainted()).toBe(true);
+    expect(playerPokemon?.isFainted()).toBe(false);
+  });
+
+  it("should not KO the opponent if the user dies to weather", async () => {
+    // Opponent will be reduced to 1 HP by False Swipe, then faint to Sandstorm
+    const moveToUse = Moves.FALSE_SWIPE;
+
+    game.override.moveset(moveToUse)
+      .ability(Abilities.SAND_STREAM);
+    await game.classicMode.startBattle(defaultParty);
+
+    const enemyPokemon = game.scene.getEnemyPokemon();
+    const playerPokemon = game.scene.getPlayerPokemon();
+
+    game.move.select(moveToUse);
+    await game.setTurnOrder(enemyFirst);
+    await game.phaseInterceptor.to("BerryPhase");
+
+    expect(enemyPokemon?.isFainted()).toBe(true);
+    expect(playerPokemon?.isFainted()).toBe(false);
+  });
+
+  it("should not KO the opponent if the user had another turn", async () => {
+    const moveToUse = Moves.TACKLE;
+
+    game.override.moveset([ Moves.SPORE, moveToUse ]);
+    await game.classicMode.startBattle(defaultParty);
+
+    const enemyPokemon = game.scene.getEnemyPokemon();
+    const playerPokemon = game.scene.getPlayerPokemon();
+
+    // Turn 1: Enemy uses Destiny Bond and doesn't faint
+    game.move.select(Moves.SPORE);
+    await game.setTurnOrder(enemyFirst);
+    await game.toNextTurn();
+
+    expect(enemyPokemon?.isFainted()).toBe(false);
+    expect(playerPokemon?.isFainted()).toBe(false);
+    expect(enemyPokemon?.status?.effect).toBe(StatusEffect.SLEEP);
+
+    // Turn 2: Enemy should skip a turn due to sleep, then get KO'd
+    game.move.select(moveToUse);
+    await game.setTurnOrder(enemyFirst);
+    await game.phaseInterceptor.to("BerryPhase");
+
+    expect(enemyPokemon?.isFainted()).toBe(true);
+    expect(playerPokemon?.isFainted()).toBe(false);
+  });
+
+  it("should not KO an ally", async () => {
+    game.override.moveset([ Moves.DESTINY_BOND, Moves.CRUNCH ])
+      .battleType("double");
+    await game.classicMode.startBattle([ Species.SHEDINJA, Species.BULBASAUR, Species.SQUIRTLE ]);
+
+    const enemyPokemon0 = game.scene.getEnemyField()[0];
+    const enemyPokemon1 = game.scene.getEnemyField()[1];
+    const playerPokemon0 = game.scene.getPlayerField()[0];
+    const playerPokemon1 = game.scene.getPlayerField()[1];
+
+    // Shedinja uses Destiny Bond, then ally Bulbasaur KO's Shedinja with Crunch
+    game.move.select(Moves.DESTINY_BOND, 0);
+    game.move.select(Moves.CRUNCH, 1, BattlerIndex.PLAYER);
+    await game.setTurnOrder([ BattlerIndex.PLAYER, BattlerIndex.PLAYER_2, BattlerIndex.ENEMY, BattlerIndex.ENEMY_2 ]);
+    await game.phaseInterceptor.to("BerryPhase");
+
+    expect(enemyPokemon0?.isFainted()).toBe(false);
+    expect(enemyPokemon1?.isFainted()).toBe(false);
+    expect(playerPokemon0?.isFainted()).toBe(true);
+    expect(playerPokemon1?.isFainted()).toBe(false);
+  });
+
+  it("should not cause a crash if the user is KO'd by Ceaseless Edge", async () => {
+    const moveToUse = Moves.CEASELESS_EDGE;
+    vi.spyOn(allMoves[moveToUse], "accuracy", "get").mockReturnValue(100);
+
+    game.override.moveset(moveToUse);
+    await game.classicMode.startBattle(defaultParty);
+
+    const enemyPokemon = game.scene.getEnemyPokemon();
+    const playerPokemon = game.scene.getPlayerPokemon();
+
+    game.move.select(moveToUse);
+    await game.setTurnOrder(enemyFirst);
+    await game.phaseInterceptor.to("BerryPhase");
+
+    expect(enemyPokemon?.isFainted()).toBe(true);
+    expect(playerPokemon?.isFainted()).toBe(true);
+
+    // Ceaseless Edge spikes effect should still activate
+    const tagAfter = game.scene.arena.getTagOnSide(ArenaTagType.SPIKES, ArenaTagSide.ENEMY) as ArenaTrapTag;
+    expect(tagAfter.tagType).toBe(ArenaTagType.SPIKES);
+    expect(tagAfter.layers).toBe(1);
+  });
+
+  it("should not cause a crash if the user is KO'd by Pledge moves", async () => {
+    game.override.moveset([ Moves.GRASS_PLEDGE, Moves.WATER_PLEDGE ])
+      .battleType("double");
+    await game.classicMode.startBattle(defaultParty);
+
+    const enemyPokemon0 = game.scene.getEnemyField()[0];
+    const enemyPokemon1 = game.scene.getEnemyField()[1];
+    const playerPokemon0 = game.scene.getPlayerField()[0];
+    const playerPokemon1 = game.scene.getPlayerField()[1];
+
+    game.move.select(Moves.GRASS_PLEDGE, 0, BattlerIndex.ENEMY);
+    game.move.select(Moves.WATER_PLEDGE, 1, BattlerIndex.ENEMY);
+    await game.setTurnOrder([ BattlerIndex.ENEMY, BattlerIndex.ENEMY_2, BattlerIndex.PLAYER, BattlerIndex.PLAYER_2 ]);
+    await game.phaseInterceptor.to("BerryPhase");
+
+    expect(enemyPokemon0?.isFainted()).toBe(true);
+    expect(enemyPokemon1?.isFainted()).toBe(false);
+    expect(playerPokemon0?.isFainted()).toBe(false);
+    expect(playerPokemon1?.isFainted()).toBe(true);
+
+    // Pledge secondary effect should still activate
+    const tagAfter = game.scene.arena.getTagOnSide(ArenaTagType.GRASS_WATER_PLEDGE, ArenaTagSide.ENEMY) as ArenaTrapTag;
+    expect(tagAfter.tagType).toBe(ArenaTagType.GRASS_WATER_PLEDGE);
+  });
+
+  /**
+   * In particular, this should prevent something like
+   * {@link https://github.com/pagefaultgames/pokerogue/issues/4219}
+   * from occurring with fainting by KO'ing a Destiny Bond user with U-Turn.
+   */
+  it("should not allow the opponent to revive via Reviver Seed", async () => {
+    const moveToUse = Moves.TACKLE;
+
+    game.override.moveset(moveToUse)
+      .startingHeldItems([{ name: "REVIVER_SEED" }]);
+    await game.classicMode.startBattle(defaultParty);
+
+    const enemyPokemon = game.scene.getEnemyPokemon();
+    const playerPokemon = game.scene.getPlayerPokemon();
+
+    game.move.select(moveToUse);
+    await game.setTurnOrder(enemyFirst);
+    await game.phaseInterceptor.to("BerryPhase");
+
+    expect(enemyPokemon?.isFainted()).toBe(true);
+    expect(playerPokemon?.isFainted()).toBe(true);
+
+    // Check that the Tackle user's Reviver Seed did not activate
+    const revSeeds = game.scene.getModifiers(PokemonInstantReviveModifier).filter(m => m.pokemonId === playerPokemon?.id);
+    expect(revSeeds.length).toBe(1);
+  });
+});