ConstTag.js — svelte Source File

Source Code

/** @import { Expression, Identifier, Pattern } from 'estree' */
/** @import { AST } from '#compiler' */
/** @import { ComponentContext } from '../types' */
/** @import { ExpressionMetadata } from '../../../nodes.js' */
import { dev } from '../../../../state.js';
import { extract_identifiers } from '../../../../utils/ast.js';
import * as b from '#compiler/builders';
import { create_derived } from '../utils.js';
import { get_value } from './shared/declarations.js';
import { build_expression } from './shared/utils.js';

/**
 * @param {AST.ConstTag} node
 * @param {ComponentContext} context
 */
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(context, declaration.init, node.metadata.expression);

		let expression = create_derived(context.state, init, node.metadata.expression.has_await);

		if (dev) {
			expression = b.call('$.tag', expression, b.literal(declaration.id.name));
		}

		context.state.transform[declaration.id.name] = { read: get_value };

		add_const_declaration(
			context.state,
			declaration.id,
			expression,
			node.metadata.expression,
			context.state.scope.get_bindings(declaration)
		);
	} else {
		const identifiers = extract_identifiers(declaration.id);
		const tmp = b.id(context.state.scope.generate('computed_const'));

		const transform = { ...context.state.transform };

		// Make all identifiers that are declared within the following computed regular
		// variables, as they are not signals in that context yet
		for (const node of identifiers) {
			delete transform[node.name];
		}

		const child_state = /** @type {ComponentContext['state']} */ ({
			...context.state,
			transform
		});

		// TODO optimise the simple `{ x } = y` case — we can just return `y`
		// instead of destructuring it only to return a new object
		const init = build_expression(
			{ ...context, state: child_state },
			declaration.init,
			node.metadata.expression
		);
// ... (75 more lines)