warn if passing slot not defined into Component

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+* In `dev` mode, display a runtime warning when a component is passed an unexpected slot ([#1020](https://github.com/sveltejs/svelte/issues/1020), [#1447](https://github.com/sveltejs/svelte/issues/1447))
 * In `vars` array, correctly indicate whether `module` variables are `mutated` or `reassigned` ([#3215](https://github.com/sveltejs/svelte/issues/3215))
 * Fix spread props not updating in certain situations ([#3521](https://github.com/sveltejs/svelte/issues/3521), [#4480](https://github.com/sveltejs/svelte/issues/4480))
 * Use the fallback content for slots if they are passed only whitespace ([#4092](https://github.com/sveltejs/svelte/issues/4092))

src/compiler/compile/render_dom/Block.ts

@@ -412,8 +412,7 @@ export default class Block {
 	}
 
 	has_content() {
-		return this.renderer.options.dev ||
-			this.first ||
+		return this.first ||
 			this.event_listeners.length > 0 ||
 			this.chunks.intro.length > 0 ||
 			this.chunks.outro.length > 0  ||

src/compiler/compile/render_dom/index.ts

@@ -264,7 +264,7 @@ export default function dom(
 		args.push(x`$$props`);
 	}
 
-	const has_create_fragment = block.has_content();
+	const has_create_fragment = component.compile_options.dev || block.has_content();
 	if (has_create_fragment) {
 		body.push(b`
 			function create_fragment(#ctx) {
@@ -412,7 +412,8 @@ export default function dom(
 
 				${unknown_props_check}
 
-				${component.slots.size ? b`let { $$slots = {}, $$scope } = $$props;` : null}
+				${component.slots.size || component.compile_options.dev ? b`let { $$slots = {}, $$scope } = $$props;` : null}
+				${component.compile_options.dev && b`@validate_slots('${component.tag}', $$slots, [${[...component.slots.keys()].map(key => `'${key}'`).join(',')}]);`}
 
 				${renderer.binding_groups.length > 0 && b`const $$binding_groups = [${renderer.binding_groups.map(_ => x`[]`)}];`}
 

src/runtime/internal/dev.ts

@@ -89,6 +89,13 @@ export function validate_each_argument(arg) {
 	}
 }
 
+export function validate_slots(name, slot, keys) {
+	for (const slot_key of Object.keys(slot)) {
+		if (!~keys.indexOf(slot_key)) {
+			console.warn(`<${name}> received an unexpected slot "${slot_key}".`);
+		}
+	}
+}
 
 type Props = Record<string, any>;
 export interface SvelteComponentDev {

test/js/samples/capture-inject-state/expected.js

@@ -14,6 +14,7 @@ import {
 	space,
 	subscribe,
 	text,
+	validate_slots,
 	validate_store
 } from "svelte/internal";
 
@@ -114,6 +115,9 @@ function instance($$self, $$props, $$invalidate) {
 		if (!~writable_props.indexOf(key) && key.slice(0, 2) !== "$$") console.warn(`<Component> was created with unknown prop '${key}'`);
 	});
 
+	let { $$slots = {}, $$scope } = $$props;
+	validate_slots("Component", $$slots, []);
+
 	$$self.$set = $$props => {
 		if ("prop" in $$props) $$subscribe_prop($$invalidate(0, prop = $$props.prop));
 		if ("alias" in $$props) $$invalidate(1, realName = $$props.alias);

test/js/samples/debug-empty/expected.js

@@ -12,7 +12,8 @@ import {
 	safe_not_equal,
 	set_data_dev,
 	space,
-	text
+	text,
+	validate_slots
 } from "svelte/internal";
 
 const file = undefined;
@@ -75,6 +76,9 @@ function instance($$self, $$props, $$invalidate) {
 		if (!~writable_props.indexOf(key) && key.slice(0, 2) !== "$$") console.warn(`<Component> was created with unknown prop '${key}'`);
 	});
 
+	let { $$slots = {}, $$scope } = $$props;
+	validate_slots("Component", $$slots, []);
+
 	$$self.$set = $$props => {
 		if ("name" in $$props) $$invalidate(0, name = $$props.name);
 	};

test/js/samples/debug-foo-bar-baz-things/expected.js

@@ -14,7 +14,8 @@ import {
 	set_data_dev,
 	space,
 	text,
-	validate_each_argument
+	validate_each_argument,
+	validate_slots
 } from "svelte/internal";
 
 const file = undefined;
@@ -179,6 +180,9 @@ function instance($$self, $$props, $$invalidate) {
 		if (!~writable_props.indexOf(key) && key.slice(0, 2) !== "$$") console.warn(`<Component> was created with unknown prop '${key}'`);
 	});
 
+	let { $$slots = {}, $$scope } = $$props;
+	validate_slots("Component", $$slots, []);
+
 	$$self.$set = $$props => {
 		if ("things" in $$props) $$invalidate(0, things = $$props.things);
 		if ("foo" in $$props) $$invalidate(1, foo = $$props.foo);

test/js/samples/debug-foo/expected.js

@@ -14,7 +14,8 @@ import {
 	set_data_dev,
 	space,
 	text,
-	validate_each_argument
+	validate_each_argument,
+	validate_slots
 } from "svelte/internal";
 
 const file = undefined;
@@ -171,6 +172,9 @@ function instance($$self, $$props, $$invalidate) {
 		if (!~writable_props.indexOf(key) && key.slice(0, 2) !== "$$") console.warn(`<Component> was created with unknown prop '${key}'`);
 	});
 
+	let { $$slots = {}, $$scope } = $$props;
+	validate_slots("Component", $$slots, []);
+
 	$$self.$set = $$props => {
 		if ("things" in $$props) $$invalidate(0, things = $$props.things);
 		if ("foo" in $$props) $$invalidate(1, foo = $$props.foo);

test/js/samples/debug-hoisted/expected.js

@@ -4,7 +4,8 @@ import {
 	dispatch_dev,
 	init,
 	noop,
-	safe_not_equal
+	safe_not_equal,
+	validate_slots
 } from "svelte/internal";
 
 const file = undefined;
@@ -56,6 +57,8 @@ function instance($$self, $$props, $$invalidate) {
 		if (!~writable_props.indexOf(key) && key.slice(0, 2) !== "$$") console.warn(`<Component> was created with unknown prop '${key}'`);
 	});
 
+	let { $$slots = {}, $$scope } = $$props;
+	validate_slots("Component", $$slots, []);
 	$$self.$capture_state = () => ({ obj, kobzol });
 
 	$$self.$inject_state = $$props => {

test/js/samples/debug-no-dependencies/expected.js

@@ -11,7 +11,8 @@ import {
 	safe_not_equal,
 	space,
 	text,
-	validate_each_argument
+	validate_each_argument,
+	validate_slots
 } from "svelte/internal";
 
 const file = undefined;
@@ -141,6 +142,8 @@ function instance($$self, $$props) {
 		if (!~writable_props.indexOf(key) && key.slice(0, 2) !== "$$") console.warn(`<Component> was created with unknown prop '${key}'`);
 	});
 
+	let { $$slots = {}, $$scope } = $$props;
+	validate_slots("Component", $$slots, []);
 	return [];
 }
 

test/js/samples/dev-warning-missing-data-computed/expected.js

@@ -12,7 +12,8 @@ import {
 	safe_not_equal,
 	set_data_dev,
 	space,
-	text
+	text,
+	validate_slots
 } from "svelte/internal";
 
 const file = undefined;
@@ -72,6 +73,9 @@ function instance($$self, $$props, $$invalidate) {
 		if (!~writable_props.indexOf(key) && key.slice(0, 2) !== "$$") console.warn(`<Component> was created with unknown prop '${key}'`);
 	});
 
+	let { $$slots = {}, $$scope } = $$props;
+	validate_slots("Component", $$slots, []);
+
 	$$self.$set = $$props => {
 		if ("foo" in $$props) $$invalidate(0, foo = $$props.foo);
 	};

test/js/samples/loop-protect/expected.js

@@ -11,7 +11,8 @@ import {
 	insert_dev,
 	loop_guard,
 	noop,
-	safe_not_equal
+	safe_not_equal,
+	validate_slots
 } from "svelte/internal";
 
 const { console: console_1 } = globals;
@@ -110,6 +111,9 @@ function instance($$self, $$props, $$invalidate) {
 		if (!~writable_props.indexOf(key) && key.slice(0, 2) !== "$$") console_1.warn(`<Component> was created with unknown prop '${key}'`);
 	});
 
+	let { $$slots = {}, $$scope } = $$props;
+	validate_slots("Component", $$slots, []);
+
 	function div_binding($$value) {
 		binding_callbacks[$$value ? "unshift" : "push"](() => {
 			$$invalidate(0, node = $$value);
@@ -161,4 +165,4 @@ class Component extends SvelteComponentDev {
 	}
 }
 
-export default Component;
+export default Component;

test/runtime/samples/component-slot-warning/Nested.svelte

@@ -0,0 +1 @@
+<slot name="slot2"></slot>

test/runtime/samples/component-slot-warning/_config.js

@@ -0,0 +1,9 @@
+export default {
+	compileOptions: {
+		dev: true
+	},
+	warnings: [
+		'<Nested> received an unexpected slot "default".',
+		'<Nested> received an unexpected slot "slot1".'
+	]
+};

test/runtime/samples/component-slot-warning/main.svelte

@@ -0,0 +1,7 @@
+<script>
+	import Nested from "./Nested.svelte";
+</script>
+<Nested>
+	<input slot="slot1">
+	<input slot="slot2">
+</Nested>