perf: cache frontmatter data

src/index.mjs

@@ -1,7 +1,5 @@
 import { visit } from "unist-util-visit";
 import * as path from "path";
-import * as fs from "fs";
-import { default as matter } from "gray-matter";
 import { default as debugFn } from "debug";
 import {
   replaceExt,
@@ -15,6 +13,7 @@ import {
   URL_PATH_SEPARATOR,
   FILE_PATH_SEPARATOR,
   shouldProcessFile,
+  getMatter,
 } from "./utils.mjs";
 import { validateOptions } from "./options.mjs";
 
@@ -63,9 +62,7 @@ function astroRehypeRelativeMarkdownLinks(opts = {}) {
       }
 
       // read gray matter from href file
-      const urlFileContent = fs.readFileSync(urlFilePath);
-      const { data: frontmatter } = matter(urlFileContent);
-      const frontmatterSlug = frontmatter.slug;
+      const { slug: frontmatterSlug } = getMatter(urlFilePath);
       const contentDir = path.resolve(options.contentPath);
       const collectionPathMode = options.collectionPathMode;
       const trailingSlashMode = options.trailingSlash;

src/utils.d.ts

@@ -23,3 +23,5 @@ export type NormaliseAstroOutputPath = (
 export type Slash = (path: string, sep: string) => string;
 export type NormalizePath = (path: string) => string;
 export type ShouldProcessFile = (path: string) => boolean;
+export type MatterData = { slug?: string };
+export type GetMatter = (path: string) => MatterData;

src/utils.mjs

@@ -1,9 +1,10 @@
 import path from "path";
-import { statSync } from "fs";
+import { readFileSync, statSync } from "fs";
 import { slug as githubSlug } from "github-slugger";
 import { z } from "zod";
 import { asError } from "catch-unknown";
 import isAbsoluteUrl from "is-absolute-url";
+import matter from "gray-matter";
 
 const validMarkdownExtensions = [".md", ".mdx"];
 const isWindows =
@@ -167,3 +168,17 @@ export function shouldProcessFile(npath) {
   // see https://github.com/withastro/astro/blob/0fec72b35cccf80b66a85664877ca9dcc94114aa/packages/astro/src/content/utils.ts#L253
   return !npath.split(path.sep).some((p) => p && p.startsWith("_"));
 }
+
+/** @type {Record<string, import('./utils.d.ts').MatterData>} */
+const matterCache = {};
+/** @type {import('./utils.d.ts').GetMatter} */
+export function getMatter(npath) {
+  const readMatter = () => {
+    const content = readFileSync(npath);
+    const { data: frontmatter } = matter(content);
+    matterCache[npath] = frontmatter;
+    return frontmatter;
+  };
+
+  return matterCache[npath] || readMatter();
+}