fix: only create async functions in SSR output when necessary (#17593)

* fix: only create async functions in SSR output when necessary

* actually...

* simplify generated code a bit more

* simplify

.changeset/hot-insects-stare.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: only create async functions in SSR output when necessary

packages/svelte/src/compiler/phases/3-transform/server/visitors/RegularElement.js

@@ -70,8 +70,7 @@ export function RegularElement(node, context) {
 		if (optimiser.expressions.length > 0) {
 			context.state.template.push(
 				create_child_block(
-					b.block([optimiser.apply(), ...state.init, ...build_template(state.template)]),
-					true
+					b.block([optimiser.apply(), ...state.init, ...build_template(state.template)])
 				)
 			);
 		} else {
@@ -133,7 +132,7 @@ export function RegularElement(node, context) {
 
 		if (optimiser.expressions.length > 0) {
 			context.state.template.push(
-				create_child_block(b.block([optimiser.apply(), ...state.init, statement]), true)
+				create_child_block(b.block([optimiser.apply(), ...state.init, statement]))
 			);
 		} else {
 			context.state.template.push(...state.init, statement);
@@ -186,7 +185,7 @@ export function RegularElement(node, context) {
 
 		if (optimiser.expressions.length > 0) {
 			context.state.template.push(
-				create_child_block(b.block([optimiser.apply(), ...state.init, statement]), true)
+				create_child_block(b.block([optimiser.apply(), ...state.init, statement]))
 			);
 		} else {
 			context.state.template.push(...state.init, statement);
@@ -236,18 +235,19 @@ export function RegularElement(node, context) {
 	}
 
 	if (optimiser.is_async()) {
-		let statement = create_child_block(
-			b.block([optimiser.apply(), ...state.init, ...build_template(state.template)]),
-			true
-		);
+		let statements = [...state.init, ...build_template(state.template)];
+
+		if (optimiser.has_await) {
+			statements = [create_child_block(b.block([optimiser.apply(), ...statements]))];
+		}
 
 		const blockers = optimiser.blockers();
 
 		if (blockers.elements.length > 0) {
-			statement = create_async_block(b.block([statement]), blockers, false, false);
+			statements = [create_async_block(b.block(statements), blockers, false, false)];
 		}
 
-		context.state.template.push(statement);
+		context.state.template.push(...statements);
 	} else {
 		context.state.init.push(...state.init);
 		context.state.template.push(...state.template);

packages/svelte/src/compiler/phases/3-transform/server/visitors/SvelteElement.js

@@ -79,7 +79,7 @@ export function SvelteElement(node, context) {
 	);
 
 	if (optimiser.expressions.length > 0) {
-		statement = create_child_block(b.block([optimiser.apply(), statement]), true);
+		statement = create_child_block(b.block([optimiser.apply(), statement]));
 	}
 
 	statements.push(statement);

packages/svelte/src/compiler/phases/3-transform/server/visitors/shared/utils.js

@@ -264,11 +264,10 @@ export function build_getter(node, state) {
 /**
  * Creates a `$$renderer.child(...)` expression statement
  * @param {BlockStatement | Expression} body
- * @param {boolean} async
  * @returns {Statement}
  */
-export function create_child_block(body, async) {
-	return b.stmt(b.call('$$renderer.child', b.arrow([b.id('$$renderer')], body, async)));
+export function create_child_block(body) {
+	return b.stmt(b.call('$$renderer.child', b.arrow([b.id('$$renderer')], body, true)));
 }
 
 /**