compiler work

packages/svelte/src/compiler/phases/2-analyze/index.js

@@ -278,7 +278,8 @@ export function analyze_module(source, options) {
 		tracing: false,
 		async_deriveds: new Set(),
 		comments,
-		classes: new Map()
+		classes: new Map(),
+		pickled_awaits: new Set()
 	};
 
 	state.adjust({
@@ -304,7 +305,8 @@ export function analyze_module(source, options) {
 			options: /** @type {ValidatedCompileOptions} */ (options),
 			fragment: null,
 			parent_element: null,
-			reactive_statement: null
+			reactive_statement: null,
+			in_derived: false
 		},
 		visitors
 	);
@@ -540,7 +542,8 @@ export function analyze_component(root, source, options) {
 		source,
 		snippet_renderers: new Map(),
 		snippets: new Set(),
-		async_deriveds: new Set()
+		async_deriveds: new Set(),
+		pickled_awaits: new Set()
 	};
 
 	if (!runes) {
@@ -699,7 +702,8 @@ export function analyze_component(root, source, options) {
 				expression: null,
 				state_fields: new Map(),
 				function_depth: scope.function_depth,
-				reactive_statement: null
+				reactive_statement: null,
+				in_derived: false
 			};
 
 			walk(/** @type {AST.SvelteNode} */ (ast), state, visitors);
@@ -766,7 +770,8 @@ export function analyze_component(root, source, options) {
 				component_slots: new Set(),
 				expression: null,
 				state_fields: new Map(),
-				function_depth: scope.function_depth
+				function_depth: scope.function_depth,
+				in_derived: false
 			};
 
 			walk(/** @type {AST.SvelteNode} */ (ast), state, visitors);

packages/svelte/src/compiler/phases/2-analyze/types.d.ts

@@ -27,6 +27,11 @@ export interface AnalysisState {
 
 	// legacy stuff
 	reactive_statement: null | ReactiveStatement;
+
+	/**
+	 * True if we're directly inside a `$derived(...)` expression (but not `$derived.by(...)`)
+	 */
+	in_derived: boolean;
 }
 
 export type Context<State extends AnalysisState = AnalysisState> = import('zimmerframe').Context<

packages/svelte/src/compiler/phases/2-analyze/visitors/AwaitExpression.js

@@ -1,14 +1,27 @@
-/** @import { AwaitExpression } from 'estree' */
+/** @import { AwaitExpression, Expression, SpreadElement, Property } from 'estree' */
 /** @import { Context } from '../types' */
+/** @import { AST } from '#compiler' */
 import * as e from '../../../errors.js';
-import * as b from '#compiler/builders';
 
 /**
  * @param {AwaitExpression} node
  * @param {Context} context
  */
 export function AwaitExpression(node, context) {
-	let suspend = context.state.ast_type === 'instance' && context.state.function_depth === 1;
+	const tla = context.state.ast_type === 'instance' && context.state.function_depth === 1;
+
+	// preserve context for
+	//   a) top-level await and
+	//   b) awaits that precede other expressions in template or `$derived(...)`
+	if (
+		tla ||
+		(is_reactive_expression(context.path, context.state.in_derived) &&
+			!is_last_evaluated_expression(context.path, node))
+	) {
+		context.state.analysis.pickled_awaits.add(node);
+	}
+
+	let suspend = tla;
 
 	if (context.state.expression) {
 		context.state.expression.has_await = true;
@@ -34,3 +47,101 @@ export function AwaitExpression(node, context) {
 
 	context.next();
 }
+
+/**
+ * @param {AST.SvelteNode[]} path
+ * @param {boolean} in_derived
+ */
+export function is_reactive_expression(path, in_derived) {
+	if (in_derived) {
+		return true;
+	}
+
+	let i = path.length;
+
+	while (i--) {
+		const parent = path[i];
+
+		if (
+			parent.type === 'ArrowFunctionExpression' ||
+			parent.type === 'FunctionExpression' ||
+			parent.type === 'FunctionDeclaration'
+		) {
+			return false;
+		}
+
+		// @ts-expect-error we could probably use a neater/more robust mechanism
+		if (parent.metadata) {
+			return true;
+		}
+	}
+
+	return false;
+}
+
+/**
+ * @param {AST.SvelteNode[]} path
+ * @param {Expression | SpreadElement | Property} node
+ */
+export function is_last_evaluated_expression(path, node) {
+	let i = path.length;
+
+	while (i--) {
+		const parent = /** @type {Expression | Property | SpreadElement} */ (path[i]);
+
+		// @ts-expect-error we could probably use a neater/more robust mechanism
+		if (parent.metadata) {
+			return true;
+		}
+
+		switch (parent.type) {
+			case 'ArrayExpression':
+				if (node !== parent.elements.at(-1)) return false;
+				break;
+
+			case 'AssignmentExpression':
+			case 'BinaryExpression':
+			case 'LogicalExpression':
+				if (node === parent.left) return false;
+				break;
+
+			case 'CallExpression':
+			case 'NewExpression':
+				if (node !== parent.arguments.at(-1)) return false;
+				break;
+
+			case 'ConditionalExpression':
+				if (node === parent.test) return false;
+				break;
+
+			case 'MemberExpression':
+				if (parent.computed && node === parent.object) return false;
+				break;
+
+			case 'ObjectExpression':
+				if (node !== parent.properties.at(-1)) return false;
+				break;
+
+			case 'Property':
+				if (node === parent.key) return false;
+				break;
+
+			case 'SequenceExpression':
+				if (node !== parent.expressions.at(-1)) return false;
+				break;
+
+			case 'TaggedTemplateExpression':
+				if (node !== parent.quasi.expressions.at(-1)) return false;
+				break;
+
+			case 'TemplateLiteral':
+				if (node !== parent.expressions.at(-1)) return false;
+				break;
+
+			default:
+				return false;
+		}
+
+		node = parent;
+	}
+}

packages/svelte/src/compiler/phases/2-analyze/visitors/CallExpression.js

@@ -241,6 +241,7 @@ export function CallExpression(node, context) {
 		context.next({
 			...context.state,
 			function_depth: context.state.function_depth + 1,
+			in_derived: true,
 			expression
 		});
 

packages/svelte/src/compiler/phases/2-analyze/visitors/ConstTag.js

@@ -35,5 +35,9 @@ export function ConstTag(node, context) {
 	const declaration = node.declaration.declarations[0];
 
 	context.visit(declaration.id);
-	context.visit(declaration.init, { ...context.state, expression: node.metadata.expression });
+	context.visit(declaration.init, {
+		...context.state,
+		expression: node.metadata.expression,
+		in_derived: true
+	});
 }

packages/svelte/src/compiler/phases/2-analyze/visitors/VariableDeclarator.js

@@ -49,6 +49,12 @@ export function VariableDeclarator(node, context) {
 			}
 		}
 
+		if (rune === '$derived') {
+			context.visit(node.id);
+			context.visit(/** @type {Expression} */ (node.init), { ...context.state, in_derived: true });
+			return;
+		}
+
 		if (rune === '$props') {
 			if (node.id.type !== 'ObjectPattern' && node.id.type !== 'Identifier') {
 				e.props_invalid_identifier(node);

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

@@ -166,7 +166,6 @@ export function client_component(analysis, options) {
 		state_fields: new Map(),
 		transform: {},
 		in_constructor: false,
-		in_derived: false,
 		instance_level_snippets: [],
 		module_level_snippets: [],
 
@@ -712,7 +711,6 @@ export function client_module(analysis, options) {
 		state_fields: new Map(),
 		transform: {},
 		in_constructor: false,
-		in_derived: false,
 		is_instance: false
 	};
 

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

@@ -6,8 +6,7 @@ import type {
 	Expression,
 	AssignmentExpression,
 	UpdateExpression,
-	VariableDeclaration,
+	VariableDeclaration
-	Declaration
 } from 'estree';
 import type { AST, Namespace, ValidatedCompileOptions } from '#compiler';
 import type { TransformState } from '../types.js';
@@ -22,11 +21,6 @@ export interface ClientTransformState extends TransformState {
 	 */
 	readonly in_constructor: boolean;
 
-	/**
-	 * True if we're directly inside a `$derived(...)` expression (but not `$derived.by(...)`)
-	 */
-	readonly in_derived: boolean;
-
 	/** `true` if we're transforming the contents of `<script>` */
 	readonly is_instance: boolean;
 

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

@@ -1,4 +1,4 @@
-/** @import { AwaitExpression, Expression, Property, SpreadElement } from 'estree' */
+/** @import { AwaitExpression, Expression } from 'estree' */
 /** @import { Context } from '../types' */
 import { dev, is_ignored } from '../../../../state.js';
 import * as b from '../../../../utils/builders.js';
@@ -10,12 +10,7 @@ import * as b from '../../../../utils/builders.js';
 export function AwaitExpression(node, context) {
 	const argument = /** @type {Expression} */ (context.visit(node.argument));
 
-	const tla = context.state.is_instance && context.state.scope.function_depth === 1;
+	if (context.state.analysis.pickled_awaits.has(node)) {
-
-	// preserve context for
-	//   a) top-level await and
-	//   b) awaits that precede other expressions in template or `$derived(...)`
-	if (tla || (is_reactive_expression(context) && !is_last_evaluated_expression(context, node))) {
 		return b.call(b.await(b.call('$.save', argument)));
 	}
 
@@ -27,100 +22,3 @@ export function AwaitExpression(node, context) {
 
 	return argument === node.argument ? node : { ...node, argument };
 }
-
-/**
- * @param {Context} context
- */
-function is_reactive_expression(context) {
-	if (context.state.in_derived) {
-		return true;
-	}
-
-	let i = context.path.length;
-
-	while (i--) {
-		const parent = context.path[i];
-
-		if (
-			parent.type === 'ArrowFunctionExpression' ||
-			parent.type === 'FunctionExpression' ||
-			parent.type === 'FunctionDeclaration'
-		) {
-			return false;
-		}
-
-		// @ts-expect-error we could probably use a neater/more robust mechanism
-		if (parent.metadata) {
-			return true;
-		}
-	}
-
-	return false;
-}
-
-/**
- * @param {Context} context
- * @param {Expression | SpreadElement | Property} node
- */
-function is_last_evaluated_expression(context, node) {
-	let i = context.path.length;
-
-	while (i--) {
-		const parent = /** @type {Expression | Property | SpreadElement} */ (context.path[i]);
-
-		// @ts-expect-error we could probably use a neater/more robust mechanism
-		if (parent.metadata) {
-			return true;
-		}
-
-		switch (parent.type) {
-			case 'ArrayExpression':
-				if (node !== parent.elements.at(-1)) return false;
-				break;
-
-			case 'AssignmentExpression':
-			case 'BinaryExpression':
-			case 'LogicalExpression':
-				if (node === parent.left) return false;
-				break;
-
-			case 'CallExpression':
-			case 'NewExpression':
-				if (node !== parent.arguments.at(-1)) return false;
-				break;
-
-			case 'ConditionalExpression':
-				if (node === parent.test) return false;
-				break;
-
-			case 'MemberExpression':
-				if (parent.computed && node === parent.object) return false;
-				break;
-
-			case 'ObjectExpression':
-				if (node !== parent.properties.at(-1)) return false;
-				break;
-
-			case 'Property':
-				if (node === parent.key) return false;
-				break;
-
-			case 'SequenceExpression':
-				if (node !== parent.expressions.at(-1)) return false;
-				break;
-
-			case 'TaggedTemplateExpression':
-				if (node !== parent.quasi.expressions.at(-1)) return false;
-				break;
-
-			case 'TemplateLiteral':
-				if (node !== parent.expressions.at(-1)) return false;
-				break;
-
-			default:
-				return false;
-		}
-
-		node = parent;
-	}
-}

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

@@ -44,9 +44,7 @@ export function CallExpression(node, context) {
 
 		case '$derived':
 		case '$derived.by': {
-			let fn = /** @type {Expression} */ (
+			let fn = /** @type {Expression} */ (context.visit(node.arguments[0]));
-				context.visit(node.arguments[0], { ...context.state, in_derived: rune === '$derived' })
-			);
 
 			return b.call('$.derived', rune === '$derived' ? b.thunk(fn) : fn);
 		}

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

@@ -16,11 +16,7 @@ export function ConstTag(node, context) {
 	const declaration = node.declaration.declarations[0];
 	// TODO we can almost certainly share some code with $derived(...)
 	if (declaration.id.type === 'Identifier') {
-		const init = build_expression(
+		const init = build_expression(context, declaration.init, node.metadata.expression);
-			{ ...context, state: { ...context.state, in_derived: true } },
-			declaration.init,
-			node.metadata.expression
-		);
 
 		let expression = create_derived(context.state, init, node.metadata.expression.has_await);
 
@@ -51,8 +47,7 @@ export function ConstTag(node, context) {
 
 		const child_state = /** @type {ComponentContext['state']} */ ({
 			...context.state,
-			transform,
+			transform
-			in_derived: true
 		});
 
 		// TODO optimise the simple `{ x } = y` case — we can just return `y`

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

@@ -202,12 +202,7 @@ export function VariableDeclaration(node, context) {
 				);
 
 				if (declarator.id.type === 'Identifier') {
-					let expression = /** @type {Expression} */ (
+					let expression = /** @type {Expression} */ (context.visit(value));
-						context.visit(value, {
-							...context.state,
-							in_derived: rune === '$derived'
-						})
-					);
 
 					if (is_async) {
 						const location = dev && !is_ignored(init, 'await_waterfall') && locate_node(init);
@@ -231,12 +226,7 @@ export function VariableDeclaration(node, context) {
 					}
 				} else {
 					const init = /** @type {CallExpression} */ (declarator.init);
-					let expression = /** @type {Expression} */ (
+					let expression = /** @type {Expression} */ (context.visit(value));
-						context.visit(value, {
-							...context.state,
-							in_derived: rune === '$derived'
-						})
-					);
 
 					let rhs = value;
 

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

@@ -10,6 +10,7 @@ import { dev, filename } from '../../../state.js';
 import { render_stylesheet } from '../css/index.js';
 import { AssignmentExpression } from './visitors/AssignmentExpression.js';
 import { AwaitBlock } from './visitors/AwaitBlock.js';
+import { AwaitExpression } from './visitors/AwaitExpression.js';
 import { CallExpression } from './visitors/CallExpression.js';
 import { ClassBody } from './visitors/ClassBody.js';
 import { Component } from './visitors/Component.js';
@@ -45,6 +46,7 @@ import { call_child_payload } from './visitors/shared/utils.js';
 const global_visitors = {
 	_: set_scope,
 	AssignmentExpression,
+	AwaitExpression,
 	CallExpression,
 	ClassBody,
 	ExpressionStatement,

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

@@ -0,0 +1,17 @@
+/** @import { AwaitExpression, Expression } from 'estree' */
+/** @import { Context } from '../types' */
+import * as b from '../../../../utils/builders.js';
+
+/**
+ * @param {AwaitExpression} node
+ * @param {Context} context
+ */
+export function AwaitExpression(node, context) {
+	const argument = /** @type {Expression} */ (context.visit(node.argument));
+
+	if (context.state.analysis.pickled_awaits.has(node)) {
+		return b.call(b.await(b.call('$.save', argument)));
+	}
+
+	return argument === node.argument ? node : { ...node, argument };
+}

packages/svelte/src/compiler/phases/types.d.ts

@@ -1,5 +1,12 @@
 import type { AST, Binding, StateField } from '#compiler';
-import type { CallExpression, ClassBody, Identifier, LabeledStatement, Program } from 'estree';
+import type {
+	AwaitExpression,
+	CallExpression,
+	ClassBody,
+	Identifier,
+	LabeledStatement,
+	Program
+} from 'estree';
 import type { Scope, ScopeRoot } from './scope.js';
 
 export interface Js {
@@ -40,6 +47,8 @@ export interface Analysis {
 
 	/** A set of deriveds that contain `await` expressions */
 	async_deriveds: Set<CallExpression>;
+	/** Awaits needing context preservation */
+	pickled_awaits: Set<AwaitExpression>;
 }
 
 export interface ComponentAnalysis extends Analysis {

packages/svelte/src/internal/server/context.js

@@ -96,3 +96,33 @@ function get_parent_context(component_context) {
 
 	return null;
 }
+
+/**
+ * Capture the current component context so that we can restore it after an async operation completes.
+ */
+function capture() {
+	var previous_component = current_component;
+
+	return function restore() {
+		current_component = previous_component;
+	};
+}
+
+/**
+ * Wraps an `await` expression in such a way that the component context that was
+ * active before the expression evaluated can be reapplied afterwards —
+ * `await a + b()` becomes `(await $.save(a))() + b()`, meaning `b()` will have access
+ * to the context of its component.
+ * @template T
+ * @param {Promise<T>} promise
+ * @returns {Promise<() => T>}
+ */
+export async function save(promise) {
+	var restore = capture();
+	var value = await promise;
+
+	return () => {
+		restore();
+		return value;
+	};
+}

packages/svelte/src/internal/server/index.js

@@ -588,7 +588,7 @@ export { attr, clsx };
 
 export { html } from './blocks/html.js';
 
-export { push, pop } from './context.js';
+export { push, pop, save } from './context.js';
 
 export { push_element, pop_element, validate_snippet_args } from './dev.js';