only inject $$props when necessary

Author: Rich-Harris

packages/svelte/src/compiler/phases/3-transform/client/transform-client.js

@@ -392,12 +392,13 @@ export function client_component(source, analysis, options) {
 
 	append_styles();
 
-	if (
+	const should_inject_context =
 		analysis.needs_context ||
 		analysis.reactive_statements.size > 0 ||
 		component_returned_object.length > 0 ||
-		options.dev
-	) {
+		options.dev;
+
+	if (should_inject_context) {
 		component_block.body.unshift(b.stmt(b.call('$.push', ...push_args)));
 
 		component_block.body.push(
@@ -439,12 +440,32 @@ export function client_component(source, analysis, options) {
 		component_block.body.unshift(b.const('$$slots', b.call('$.sanitize_slots', b.id('$$props'))));
 	}
 
+	let should_inject_props =
+		should_inject_context ||
+		analysis.uses_props ||
+		analysis.uses_rest_props ||
+		analysis.uses_slots ||
+		analysis.slot_names.size > 0;
+
+	if (!should_inject_props) {
+		for (const declaration of analysis.instance.scope.declarations.values()) {
+			if (
+				declaration.kind === 'prop' ||
+				declaration.kind === 'bindable_prop' ||
+				declaration.kind === 'rest_prop'
+			) {
+				should_inject_props = true;
+				break;
+			}
+		}
+	}
+
 	const body = [
 		...state.hoisted,
 		...module.body,
 		b.function_declaration(
 			b.id(analysis.name),
-			[b.id('$$anchor'), b.id('$$props')],
+			should_inject_props ? [b.id('$$anchor'), b.id('$$props')] : [b.id('$$anchor')],
 			component_block
 		)
 	];

packages/svelte/tests/snapshot/samples/bind-component-snippet/_expected/client/index.svelte.js

@@ -7,7 +7,7 @@ import TextInput from './Child.svelte';
 var root_1 = $.template(`Something`, 1);
 var root = $.template(`<!> `, 1);
 
-function Bind_component_snippet($$anchor, $$props) {
+function Bind_component_snippet($$anchor) {
 	let value = $.source('');
 	const _snippet = snippet;
 	var fragment_1 = root();

packages/svelte/tests/snapshot/samples/dynamic-attributes-casing/_expected/client/main.svelte.js

@@ -5,7 +5,7 @@ import * as $ from "svelte/internal/client";
 
 var root = $.template(`<div></div> <svg></svg> <custom-element></custom-element> <div></div> <svg></svg> <custom-element></custom-element>`, 3);
 
-function Main($$anchor, $$props) {
+function Main($$anchor) {
 	// needs to be a snapshot test because jsdom does auto-correct the attribute casing
 	let x = 'test';
 	let y = () => 'test';

packages/svelte/tests/snapshot/samples/function-prop-no-getter/_expected/client/index.svelte.js

@@ -3,7 +3,7 @@
 import "svelte/internal/disclose-version";
 import * as $ from "svelte/internal/client";
 
-function Function_prop_no_getter($$anchor, $$props) {
+function Function_prop_no_getter($$anchor) {
 	let count = $.source(0);
 
 	function onmouseup() {

packages/svelte/tests/snapshot/samples/state-proxy-literal/_expected/client/index.svelte.js

@@ -12,7 +12,7 @@ function reset(_, str, tpl) {
 
 var root = $.template(`<input> <input> <button>reset</button>`, 1);
 
-function State_proxy_literal($$anchor, $$props) {
+function State_proxy_literal($$anchor) {
 	let str = $.source('');
 	let tpl = $.source(``);
 	var fragment = root();