fix bitmask overflow if initial dirty value

src/compiler/compile/render_dom/Renderer.ts

@@ -230,6 +230,7 @@ export default class Renderer {
 			return bitmask;
 		};
 
+		// TODO: context-overflow make it less gross
 		return {
 			// Using a ParenthesizedExpression allows us to create
 			// the expression lazily. TODO would be better if

src/compiler/compile/render_dom/wrappers/IfBlock.ts

@@ -288,7 +288,7 @@ export default class IfBlockWrapper extends Wrapper {
 		}
 
 		block.chunks.init.push(b`
-			let ${current_block_type} = ${select_block_type}(#ctx, -1);
+			let ${current_block_type} = ${select_block_type}(#ctx, ${this.get_initial_dirty_bit()});
 			let ${name} = ${get_block};
 		`);
 
@@ -407,12 +407,12 @@ export default class IfBlockWrapper extends Wrapper {
 
 		if (has_else) {
 			block.chunks.init.push(b`
-				${current_block_type_index} = ${select_block_type}(#ctx, -1);
+				${current_block_type_index} = ${select_block_type}(#ctx, ${this.get_initial_dirty_bit()});
 				${name} = ${if_blocks}[${current_block_type_index}] = ${if_block_creators}[${current_block_type_index}](#ctx);
 			`);
 		} else {
 			block.chunks.init.push(b`
-				if (~(${current_block_type_index} = ${select_block_type}(#ctx, -1))) {
+				if (~(${current_block_type_index} = ${select_block_type}(#ctx, ${this.get_initial_dirty_bit()}))) {
 					${name} = ${if_blocks}[${current_block_type_index}] = ${if_block_creators}[${current_block_type_index}](#ctx);
 				}
 			`);
@@ -587,4 +587,18 @@ export default class IfBlockWrapper extends Wrapper {
 			`);
 		}
 	}
+
+	get_initial_dirty_bit() {
+		const _this = this;
+		// TODO: context-overflow make it less gross
+
+		const val = x`-1`;
+		return {
+			...val,
+			elements: [val],
+			get type() {
+				return _this.renderer.context_overflow ? 'ArrayExpression' : 'UnaryExpression';
+			},
+		};
+	}
 }

src/compiler/compile/render_dom/wrappers/shared/get_slot_definition.ts

@@ -63,7 +63,7 @@ export function get_slot_definition(block: Block, scope: TemplateScope, lets: Le
 	const { context_lookup } = block.renderer;
 
 	// i am well aware that this code is gross
-	// TODO make it less gross
+	// TODO: context-overflow make it less gross
 	const changes = {
 		type: 'ParenthesizedExpression',
 		get expression() {

test/runtime/samples/bitmask-overflow-if/_config.js

@@ -0,0 +1,24 @@
+export default {
+	html: `
+		012345678910111213141516171819202122232425262728293031323334353637383940
+		expected: true
+		if: true
+		<button></button>
+	`,
+
+	async test({ assert, component, target, window }) {
+		const button = target.querySelector("button");
+		await button.dispatchEvent(new window.MouseEvent("click"));
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+			112345678910111213141516171819202122232425262728293031323334353637383940
+			expected: false
+			if: false
+			<div></div>
+			<button></button>
+		`
+		);
+	}
+};

test/runtime/samples/bitmask-overflow-if/main.svelte

@@ -0,0 +1,62 @@
+<script>
+	import { fade } from 'svelte/transition';
+	export let _a = [];
+	export let _0 = '0';
+	export let _1 = '1';
+	export let _2 = '2';
+	export let _3 = '3';
+	export let _4 = '4';
+	export let _5 = '5';
+	export let _6 = '6';
+	export let _7 = '7';
+	export let _8 = '8';
+	export let _9 = '9';
+	export let _10 = '10';
+	export let _11 = '11';
+	export let _12 = '12';
+	export let _13 = '13';
+	export let _14 = '14';
+	export let _15 = '15';
+	export let _16 = '16';
+	export let _17 = '17';
+	export let _18 = '18';
+	export let _19 = '19';
+	export let _20 = '20';
+	export let _21 = '21';
+	export let _22 = '22';
+	export let _23 = '23';
+	export let _24 = '24';
+	export let _25 = '25';
+	export let _26 = '26';
+	export let _27 = '27';
+	export let _28 = '28';
+	export let _29 = '29';
+	export let _30 = '30';
+	export let _31 = '31';
+	export let _32 = '32';
+	export let _33 = '33';
+	export let _34 = '34';
+	export let _35 = '35';
+	export let _36 = '36';
+	export let _37 = '37';
+	export let _38 = '38';
+	export let _39 = '39';
+	export let _40 = '40';
+
+	function update() {
+		_0 = '1';
+	}
+</script>
+
+
+{_0}{_1}{_2}{_3}{_4}{_5}{_6}{_7}{_8}{_9}{_10}{_11}{_12}{_13}{_14}{_15}{_16}{_17}{_18}{_19}{_20}{_21}{_22}{_23}{_24}{_25}{_26}{_27}{_28}{_29}{_30}{_31}{_32}{_33}{_34}{_35}{_36}{_37}{_38}{_39}{_40}
+
+expected: {_a.indexOf(_0) && _0 === '0' && _1 === '1'}
+{#if _a.indexOf(_0) && _0 === '0' && _1 === '1'}
+if: true
+{:else}
+if: false
+<div out:fade></div>
+{/if}
+
+<button on:click={update}></button>