svelte/compiler/parse/read/expression.js

import { parseExpressionAt } from 'acorn';

export default function readExpression ( parser ) {
	try {
		const node = parseExpressionAt( parser.template, parser.index );
		parser.index = node.end;

		// TODO check it's a valid expression. probably shouldn't have
		// [arrow] function expressions, etc

		return node;
	} catch ( err ) {
		parser.acornError( err );
	}
}