src/generators/Generator.js/Generator/constructor
class Generator:	constructor ( parsed, source, name, options ) {
		this.parsed = parsed;
		this.source = source;
		this.name = name;
		this.options = options;

		this.imports = [];
		this.helpers = new Set();
		this.components = new Set();
		this.events = new Set();
		this.importedComponents = new Map();

		this.bindingGroups = [];

		// track which properties are needed, so we can provide useful info
		// in dev mode
		this.expectedProperties = new Set();

		this.code = new MagicString( source );
		this.css = parsed.css ? processCss( parsed, this.code ) : null;
		this.cssId = parsed.css ? `svelte-${parsed.hash}` : '';
		this.usesRefs = false;

		// allow compiler to deconflict user's `import { get } from 'whatever'` and
		// Svelte's builtin `import { get, ... } from 'svelte/shared.js'`;
		this.importedNames = new Set();
		this.aliases = new Map();
		this._usedNames = new Set( [ name ] );
	}