Gen 5-7: Fix Snatch + Swallow interaction (#10698)

data/mods/gen4/moves.ts

@@ -1541,6 +1541,12 @@ export const Moves: import('../../../sim/dex-moves').ModdedMoveDataTable = {
 			}
 		},
 	},
+	swallow: {
+		inherit: true,
+		onTry(source) {
+			return !!source.volatiles['stockpile'];
+		},
+	},
 	switcheroo: {
 		inherit: true,
 		onTryHit(target, source, move) {

data/moves.ts

@@ -19284,12 +19284,14 @@ export const Moves: import('../sim/dex-moves').MoveDataTable = {
 		pp: 10,
 		priority: 0,
 		flags: {snatch: 1, heal: 1, metronome: 1},
-		onTry(source) {
+		onTry(source, target, move) {
+			if (move.sourceEffect === 'snatch') return;
 			return !!source.volatiles['stockpile'];
 		},
 		onHit(pokemon) {
+			const layers = pokemon.volatiles['stockpile']?.layers || 1;
 			const healAmount = [0.25, 0.5, 1];
-			const success = !!this.heal(this.modify(pokemon.maxhp, healAmount[(pokemon.volatiles['stockpile'].layers - 1)]));
+			const success = !!this.heal(this.modify(pokemon.maxhp, healAmount[layers - 1]));
 			if (!success) this.add('-fail', pokemon, 'heal');
 			pokemon.removeVolatile('stockpile');
 			return success || this.NOT_FAIL;

test/sim/moves/snatch.js

@@ -76,6 +76,34 @@ describe('Snatch', function () {
 		assert.atMost(battle.p1.active[1].hp, weavileHp, 'should not allow Snatch to bypass Heal Block');
 		assert(battle.log[battle.lastMoveLine + 2].startsWith('|cant'), 'should log that Recover failed');
 	});
+
+	it('should not snatch Swallow if the Swallow user has no Stockpiles', () => {
+		battle = common.createBattle({gameType: 'doubles'}, [[
+			{species: 'mandibuzz', moves: ['snatch']},
+			{species: 'accelgor', moves: ['swallow']},
+		], [
+			{species: 'surskit', moves: ['quickattack']},
+			{species: 'wingull', moves: ['quickattack']},
+		]]);
+
+		battle.makeChoices('auto', 'move quickattack 1, move quickattack 2');
+		for (const line of battle.log) {
+			assert(!line.includes('-activate'), `Snatch should not have activated, but found -activate message ${line}`);
+		}
+	});
+
+	it('Snatched Swallow should heal the snatcher by 25% if the snatcher has no Stockpiles', () => {
+		battle = common.createBattle([[
+			{species: 'clefable', moves: ['sleeptalk', 'bellydrum', 'snatch']},
+		], [
+			{species: 'dewgong', moves: ['stockpile', 'swallow']},
+		]]);
+		battle.makeChoices('move bellydrum', 'auto');
+		battle.makeChoices();
+		battle.makeChoices();
+		const targetHP = battle.modify(battle.p1.active[0].maxhp, 0.25);
+		assert.hurtsBy(battle.p1.active[0], -targetHP, () => battle.makeChoices('move snatch', 'move swallow'));
+	});
 });
 
 describe('Snatch [Gen 4]', function () {