disallow named slots inheriting let: scope from default slots

src/compiler/compile/nodes/InlineComponent.ts

@@ -5,7 +5,6 @@ import Binding from './Binding';
 import EventHandler from './EventHandler';
 import Expression from './shared/Expression';
 import Component from '../Component';
-import Let from './Let';
 import TemplateScope from './shared/TemplateScope';
 import { INode } from './interfaces';
 import { TemplateNode } from '../../interfaces';
@@ -18,7 +17,6 @@ export default class InlineComponent extends Node {
 	attributes: Attribute[] = [];
 	bindings: Binding[] = [];
 	handlers: EventHandler[] = [];
-	lets: Let[] = [];
 	css_custom_properties: Attribute[] = [];
 	children: INode[];
 	scope: TemplateScope;
@@ -40,6 +38,7 @@ export default class InlineComponent extends Node {
 			? new Expression(component, this, scope, info.expression)
 			: null;
 
+		const let_attributes = [];
 		info.attributes.forEach(node => {
 			/* eslint-disable no-fallthrough */
 			switch (node.type) {
@@ -68,7 +67,7 @@ export default class InlineComponent extends Node {
 					break;
 
 				case 'Let':
-					this.lets.push(new Let(component, this, scope, node));
+					let_attributes.push(node);
 					break;
 
 				case 'Transition':
@@ -83,19 +82,7 @@ export default class InlineComponent extends Node {
 			/* eslint-enable no-fallthrough */
 		});
 
-		if (this.lets.length > 0) {
+		this.scope = scope;
-			this.scope = scope.child();
-
-			this.lets.forEach(l => {
-				const dependencies = new Set([l.name.name]);
-
-				l.names.forEach(name => {
-					this.scope.add(name, dependencies, this);
-				});
-			});
-		} else {
-			this.scope = scope;
-		}
 
 		this.handlers.forEach(handler => {
 			handler.modifiers.forEach(modifier => {
@@ -156,6 +143,24 @@ export default class InlineComponent extends Node {
 			});
 		}
 
+		if (let_attributes.length) {
+			let warned = false;
+			// copy let: attribute from <Component /> to <svelte:fragment slot="default" />
+			// as they are for `slot="default"` only
+			children.forEach(child => {
+				const slot = child.attributes.find(attribute => attribute.name === 'slot');
+				if (!slot || slot.value[0].data === 'default') {
+					child.attributes.push(...let_attributes);
+				} else if (!warned) {
+					component.warn(info, {
+						code: 'let-on-component',
+						message: 'let: bindings on Component are meant for default slot template only, it is better to define them on <svelte:fragment slot="default"> instead.'
+					});
+					warned = true;
+				}
+			});
+		}
+
 		this.children = map_children(component, this, this.scope, children);
 	}
 

src/compiler/compile/render_dom/wrappers/InlineComponent/index.ts

@@ -14,7 +14,6 @@ import is_dynamic from '../shared/is_dynamic';
 import bind_this from '../shared/bind_this';
 import { Node, Identifier, ObjectExpression } from 'estree';
 import EventHandler from '../Element/EventHandler';
-import { extract_names } from 'periscopic';
 import mark_each_block_bindings from '../shared/mark_each_block_bindings';
 import { string_to_member_expression } from '../../../utils/string_to_member_expression';
 import SlotTemplate from '../../../nodes/SlotTemplate';
@@ -80,12 +79,6 @@ export default class InlineComponentWrapper extends Wrapper {
 		};
 
 		if (this.node.children.length) {
-			this.node.lets.forEach(l => {
-				extract_names(l.value || l.name).forEach(name => {
-					renderer.add_to_context(name, true);
-				});
-			});
-
 			this.children = this.node.children.map(child => new SlotTemplateWrapper(renderer, block, this, child as SlotTemplate, strip_whitespace, next_sibling));
 		}
 

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

@@ -47,11 +47,6 @@ export default class SlotTemplateWrapper extends Wrapper {
 		});
 		this.renderer.blocks.push(this.block);
 
-		const seen = new Set(lets.map(l => l.name.name));
-		this.parent.node.lets.forEach(l => {
-			if (!seen.has(l.name.name)) lets.push(l);
-		});
-
 		this.parent.set_slot(
 			slot_template_name,
 			get_slot_definition(this.block, scope, lets)

src/compiler/compile/render_ssr/handlers/SlotTemplate.ts

@@ -14,12 +14,6 @@ export default function(node: SlotTemplate, renderer: Renderer, options: RenderO
 	renderer.push();
 	renderer.render(children, options);
 
-	const lets = node.lets;
-	const seen = new Set(lets.map(l => l.name.name));
-	parent_inline_component.lets.forEach(l => {
-		if (!seen.has(l.name.name)) lets.push(l);
-	});
-
 	const slot_fragment_content = renderer.pop();
 	if (!is_empty_template_literal(slot_fragment_content)) {
 		if (options.slot_scopes.has(node.slot_template_name)) {

test/runtime/samples/component-slot-named-inherits-default-lets/_config.js

@@ -3,7 +3,7 @@ export default {
 		<div>
 			<p>count in default slot: 0</p>
 			<p slot="foo">count in foo slot: 0</p>
-			<p slot="bar">count in bar slot: undefined</p>
+			<p slot="bar">count in bar slot: 42</p>
 			<button>+1</button>
 		</div>
 	`,
@@ -17,7 +17,7 @@ export default {
 			<div>
 				<p>count in default slot: 1</p>
 				<p slot="foo">count in foo slot: 1</p>
-				<p slot="bar">count in bar slot: undefined</p>
+				<p slot="bar">count in bar slot: 42</p>
 				<button>+1</button>
 			</div>
 		`);

test/runtime/samples/component-slot-named-inherits-default-lets/main.svelte

@@ -1,5 +1,6 @@
 <script>
 	import Nested from './Nested.svelte';
+	let count = 42;
 </script>
 
 <Nested let:count>

test/validator/samples/lets-on-component/input.svelte

@@ -0,0 +1,27 @@
+<script>
+	import Nested from './Nested.svelte';
+</script>
+
+<Nested let:count>
+	<p>
+		count in default slot: {count}
+	</p>
+	<p slot="bar">
+		count in bar slot: {count}
+	</p>
+</Nested>
+
+<Nested let:count>
+	<p>
+		count in default slot: {count}
+	</p>
+	<p>
+		count in bar slot: {count}
+	</p>
+</Nested>
+
+<Nested let:count>
+	<p slot="bar">
+		count in bar slot: {count}
+	</p>
+</Nested>

test/validator/samples/lets-on-component/warnings.json

@@ -0,0 +1,62 @@
+[
+	{
+		"code": "let-on-component",
+		"message": "let: bindings on Component are meant for default slot template only, it is better to define them on <svelte:fragment slot=\"default\"> instead.",
+		"pos": 59,
+		"start": {
+			"character": 59,
+			"column": 0,
+			"line": 5
+		},
+		"end": {
+			"character": 182,
+			"column": 9,
+			"line": 12
+		}
+	},
+	{
+		"code": "missing-declaration",
+		"message": "'count' is not defined",
+		"pos": 160,
+		"start": {
+			"character": 160,
+			"column": 22,
+			"line": 10
+		},
+		"end": {
+			"character": 165,
+			"column": 27,
+			"line": 10
+		}
+	},
+	{
+		"code": "let-on-component",
+		"message": "let: bindings on Component are meant for default slot template only, it is better to define them on <svelte:fragment slot=\"default\"> instead.",
+		"pos": 298,
+		"start": {
+			"character": 298,
+			"column": 0,
+			"line": 23
+		},
+		"end": {
+			"character": 377,
+			"column": 9,
+			"line": 27
+		}
+	},
+	{
+		"code": "missing-declaration",
+		"message": "'count' is not defined",
+		"pos": 355,
+		"start": {
+			"character": 355,
+			"column": 22,
+			"line": 25
+		},
+		"end": {
+			"character": 360,
+			"column": 27,
+			"line": 25
+		}
+	}
+]