Function grammar

lib/html/syntax.js:7301–7350

(input, visitors, options)

 * @param {HtmlProcessOptions} options process options
 */
const grammar = (input, visitors, options) => {
	// Babel's `path.skip()`, children-only. Reset per `enter` dispatch.
	let skipFlag = false;
	const visitorCtx = {
		skipChildren() {
			skipFlag = true;
		}
	};

	/**
	 * Fetches the node's visitor bucket once (reused for enter + exit) and uses
	 * index loops — `for…of` would allocate an iterator per node on this hot path.
	 * @param {HtmlVisitableNode} node subtree root
	 * @param {HtmlVisitableNode | null} parent enclosing node
	 */
	const walk = (node, parent) => {
		const b = visitors[node.type];
		let skip = false;
		if (b !== undefined && b.enter.length !== 0) {
			skipFlag = false;
			const e = b.enter;
			for (let i = 0; i < e.length; i++) e[i](node, parent, visitorCtx);
			skip = skipFlag;
			skipFlag = false;
		}
		if (!skip) {
			if (node.type === NodeType.Element) {
				// `<template>` children live in a separate content fragment, not in
				// `children` — walk it first so template content is not skipped.
				const tc = node.templateContent;
				if (tc !== undefined) walk(tc, node);
				const c = node.children;
				for (let i = 0; i < c.length; i++) walk(c[i], node);
			} else if (
				node.type === NodeType.Document ||
				node.type === NodeType.DocumentFragment
			) {
				const c = node.children;
				for (let i = 0; i < c.length; i++) walk(c[i], node);
			}
			// All other types are leaves.
		}
		if (b !== undefined) {
			const x = b.exit;
			for (let i = 0; i < x.length; i++) x[i](node, parent, visitorCtx);
		}
	};

	walk(options.ast || buildHtmlAst(input, options.fragmentContext), null);
};

/**
 * The generic visitor coordinator (`util/SourceProcessor`) bound to the HTML