svelte/src/compiler/compile/nodes/Binding.ts

import Node from './shared/Node';
import get_object from '../utils/get_object';
import Expression from './shared/Expression';
import Component from '../Component';
import TemplateScope from './shared/TemplateScope';
import {dimensions} from "../../utils/patterns";
import { Node as ESTreeNode } from 'estree';

// TODO this should live in a specific binding
const read_only_media_attributes = new Set([
	'duration',
	'buffered',
	'seekable',
	'played',
	'seeking',
	'ended',
	'videoHeight',
	'videoWidth'
]);

export default class Binding extends Node {
	type: 'Binding';
	name: string;
	expression: Expression;
	raw_expression: ESTreeNode; // TODO exists only for bind:this — is there a more elegant solution?
	is_contextual: boolean;
	is_readonly: boolean;

	constructor(component: Component, parent, scope: TemplateScope, info) {
		super(component, parent, scope, info);

		if (info.expression.type !== 'Identifier' && info.expression.type !== 'MemberExpression') {
			component.error(info, {
				code: 'invalid-directive-value',
				message: 'Can only bind to an identifier (e.g. `foo`) or a member expression (e.g. `foo.bar` or `foo[baz]`)'
			});
		}

		this.name = info.name;
		this.expression = new Expression(component, this, scope, info.expression);
		this.raw_expression = JSON.parse(JSON.stringify(info.expression));

		const { name } = get_object(this.expression.node);
		this.is_contextual = scope.names.has(name);

		// make sure we track this as a mutable ref
		if (scope.is_let(name)) {
			component.error(this, {
				code: 'invalid-binding',
				message: 'Cannot bind to a variable declared with the let: directive'
			});
		} else if (this.is_contextual) {
			if (scope.is_await(name)) {
				component.error(this, {
					code: 'invalid-binding',
					message: 'Cannot bind to a variable declared with {#await ... then} or {:catch} blocks'
				});
			}

			scope.dependencies_for_name.get(name).forEach(name => {
				const variable = component.var_lookup.get(name);
				if (variable) {
					variable.mutated = true;
				}
			});
		} else {
			const variable = component.var_lookup.get(name);

			if (!variable || variable.global) component.error(this.expression.node, {
				code: 'binding-undeclared',
				message: `${name} is not declared`
			});

			variable[this.expression.node.type === 'MemberExpression' ? 'mutated' : 'reassigned'] = true;

			if (info.expression.type === 'Identifier' && !variable.writable) component.error(this.expression.node, {
				code: 'invalid-binding',
				message: 'Cannot bind to a variable which is not writable',
			});
		}

		const type = parent.get_static_attribute_value('type');

		this.is_readonly = (
			dimensions.test(this.name) ||
			(parent.is_media_node && parent.is_media_node() && read_only_media_attributes.has(this.name)) ||
			(parent.name === 'input' && type === 'file') // TODO others?
		);
	}

	is_readonly_media_attribute() {
		return read_only_media_attributes.has(this.name);
	}
}