parallelize `await` expressions in instance

packages/svelte/src/compiler/phases/3-transform/client/types.d.ts

@@ -90,10 +90,10 @@ export interface ComponentClientTransformState extends ClientTransformState {
 
 export interface ParallelizedChunk {
 	declarators: Array<{
-		id: Pattern;
+		id: Pattern | null;
 		init: Expression;
 	}>;
-	kind: VariableDeclaration['kind'];
+	kind: VariableDeclaration['kind'] | null;
 	/** index in instance body */
 	position: number;
 	bindings: Binding[];

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

@@ -1,13 +1,16 @@
-/** @import { Expression, ExpressionStatement } from 'estree' */
-/** @import { ComponentContext } from '../types' */
+/** @import { Expression, ExpressionStatement, Node, Program } from 'estree' */
+/** @import { ComponentContext, ParallelizedChunk } from '../types' */
 import * as b from '#compiler/builders';
 import { get_rune } from '../../../scope.js';
+import { can_be_parallelized } from '../utils.js';
 
 /**
  * @param {ExpressionStatement} node
  * @param {ComponentContext} context
  */
 export function ExpressionStatement(node, context) {
+	const parent = /** @type {Node} */ (context.path.at(-1));
+	const position = /** @type {Program} */ (parent).body?.indexOf?.(node);
 	if (node.expression.type === 'CallExpression') {
 		const rune = get_rune(node.expression, context.state.scope);
 
@@ -25,6 +28,39 @@ export function ExpressionStatement(node, context) {
 			return b.empty;
 		}
 	}
+	if (
+		node.expression.type === 'AwaitExpression' &&
+		context.state.analysis.instance?.scope === context.state.scope
+	) {
+		const current_chunk = context.state.current_parallelized_chunk;
+		const parallelize = can_be_parallelized(
+			node.expression.argument,
+			context.state.scope,
+			context.state.analysis,
+			current_chunk?.bindings ?? []
+		);
+		if (parallelize) {
+			const declarator = {
+				id: null,
+				init: /** @type {Expression} */ (context.visit(node.expression))
+			};
+			if (current_chunk) {
+				current_chunk.declarators.push(declarator);
+				current_chunk.position = position;
+			} else {
+				/** @type {ParallelizedChunk} */
+				const chunk = {
+					kind: null,
+					declarators: [declarator],
+					position,
+					bindings: []
+				};
+				context.state.current_parallelized_chunk = chunk;
+				context.state.parallelized_chunks.push(chunk);
+			}
+			return;
+		}
+	}
 
 	context.next();
 }

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

@@ -148,20 +148,28 @@ export function Program(node, context) {
 		for (const chunk of context.state.parallelized_chunks) {
 			if (chunk.declarators.length === 1) {
 				const declarator = chunk.declarators[0];
-				body.splice(
-					chunk.position + offset,
-					0,
-					b.declaration(chunk.kind, [
-						b.declarator(declarator.id, b.call(b.await(b.call('$.save', declarator.init))))
-					])
-				);
+				if (declarator.id === null || chunk.kind === null) {
+					body.splice(
+						chunk.position + offset,
+						0,
+						b.stmt(b.call(b.await(b.call('$.save', declarator.init))))
+					);
+				} else {
+					body.splice(
+						chunk.position + offset,
+						0,
+						b.declaration(chunk.kind, [
+							b.declarator(declarator.id, b.call(b.await(b.call('$.save', declarator.init))))
+						])
+					);
+				}
 			} else {
 				const pattern = b.array_pattern(chunk.declarators.map(({ id }) => id));
-				const init = b.call(`$.all`, ...chunk.declarators.map(({ init }) => init));
+				const init = b.call('$.all', ...chunk.declarators.map(({ init }) => init));
 				body.splice(
 					chunk.position + offset,
 					0,
-					b.declaration(chunk.kind, [b.declarator(pattern, b.await(init))])
+					b.declaration(chunk.kind ?? 'const', [b.declarator(pattern, b.await(init))])
 				);
 			}
 			offset++;

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

@@ -69,10 +69,14 @@ export function VariableDeclaration(node, context) {
 							id,
 							init: /** @type {Expression} */ (visited_init)
 						};
-						if (current_chunk && current_chunk.kind === node.kind) {
+						if (
+							current_chunk &&
+							(current_chunk.kind === node.kind || current_chunk.kind === null)
+						) {
 							current_chunk.declarators.push(_declarator);
 							current_chunk.bindings.push(...bindings);
 							current_chunk.position = /** @type {Program} */ (parent).body.indexOf(node);
+							current_chunk.kind = node.kind;
 						} else {
 							/** @type {ParallelizedChunk} */
 							const chunk = {
@@ -370,10 +374,11 @@ export function VariableDeclaration(node, context) {
 						id,
 						init: /** @type {Expression} */ (init)
 					}));
-					if (current_chunk && current_chunk.kind === node.kind) {
+					if (current_chunk && (current_chunk.kind === node.kind || current_chunk.kind === null)) {
 						current_chunk.declarators.push(...declarators);
 						current_chunk.bindings.push(...bindings);
 						current_chunk.position = position;
+						current_chunk.kind = node.kind;
 					} else {
 						/** @type {ParallelizedChunk} */
 						const chunk = {