Change frontmatter injection ordering

.changeset/beige-pumpkins-pump.md

@@ -0,0 +1,47 @@
+---
+'astro': major
+'@astrojs/markdown-remark': major
+'@astrojs/mdx': minor
+---
+
+Give remark and rehype plugins access to user frontmatter via frontmatter injection. This means `data.astro.frontmatter` is now the _complete_ Markdown or MDX document's frontmatter, rather than an empty object.
+
+This allows plugin authors to modify existing frontmatter, or compute new properties based on other properties. For example, say you want to compute a full image URL based on an `imageSrc` slug in your document frontmatter:
+
+```ts
+export function remarkInjectSocialImagePlugin() {
+  return function (tree, file) {
+    const { frontmatter } = file.data.astro;
+    frontmatter.socialImageSrc = new URL(
+      frontmatter.imageSrc,
+      'https://my-blog.com/',
+    ).pathname;
+  }
+}
+```
+
+#### Content Collections - new `remarkPluginFrontmatter` property
+
+We have changed _inject_ frontmatter to _modify_ frontmatter in our docs to improve discoverability. This is based on support forum feedback, where "injection" is rarely the term used.
+
+To reflect this, the `injectedFrontmatter` property has been renamed to `remarkPluginFrontmatter`. This should clarify this plugin is still separate from the `data` export Content Collections expose today.
+
+
+#### Migration instructions
+
+Plugin authors should now **check for user frontmatter when applying defaults.**
+
+For example, say a remark plugin wants to apply a default `title` if none is present. Add a conditional to check if the property is present, and update if none exists:
+
+```diff
+export function remarkInjectTitlePlugin() {
+  return function (tree, file) {
+    const { frontmatter } = file.data.astro;
++    if (!frontmatter.title) {
+      frontmatter.title = 'Default title';
++    }
+  }
+}
+```
+
+This differs from previous behavior, where a Markdown file's frontmatter would _always_ override frontmatter injected via remark or reype.

examples/with-content/src/content/types.generated.d.ts

@@ -37,49 +37,50 @@ declare module 'astro:content' {
 		render(): Promise<{
 			Content: import('astro').MarkdownInstance<{}>['Content'];
 			headings: import('astro').MarkdownHeading[];
-			injectedFrontmatter: Record<string, any>;
+			remarkPluginFrontmatter: Record<string, any>;
 		}>;
 	};
 
 	const entryMap: {
-		blog: {
-			'first-post.md': {
-				id: 'first-post.md';
-				slug: 'first-post';
-				body: string;
-				collection: 'blog';
-				data: InferEntrySchema<'blog'>;
-			};
-			'markdown-style-guide.md': {
-				id: 'markdown-style-guide.md';
-				slug: 'markdown-style-guide';
-				body: string;
-				collection: 'blog';
-				data: InferEntrySchema<'blog'>;
-			};
-			'second-post.md': {
-				id: 'second-post.md';
-				slug: 'second-post';
-				body: string;
-				collection: 'blog';
-				data: InferEntrySchema<'blog'>;
-			};
-			'third-post.md': {
-				id: 'third-post.md';
-				slug: 'third-post';
-				body: string;
-				collection: 'blog';
-				data: InferEntrySchema<'blog'>;
-			};
-			'using-mdx.mdx': {
-				id: 'using-mdx.mdx';
-				slug: 'using-mdx';
-				body: string;
-				collection: 'blog';
-				data: InferEntrySchema<'blog'>;
-			};
-		};
+		"blog": {
+"first-post.md": {
+  id: "first-post.md",
+  slug: "first-post",
+  body: string,
+  collection: "blog",
+  data: InferEntrySchema<"blog">
+},
+"markdown-style-guide.md": {
+  id: "markdown-style-guide.md",
+  slug: "markdown-style-guide",
+  body: string,
+  collection: "blog",
+  data: InferEntrySchema<"blog">
+},
+"second-post.md": {
+  id: "second-post.md",
+  slug: "second-post",
+  body: string,
+  collection: "blog",
+  data: InferEntrySchema<"blog">
+},
+"third-post.md": {
+  id: "third-post.md",
+  slug: "third-post",
+  body: string,
+  collection: "blog",
+  data: InferEntrySchema<"blog">
+},
+"using-mdx.mdx": {
+  id: "using-mdx.mdx",
+  slug: "using-mdx",
+  body: string,
+  collection: "blog",
+  data: InferEntrySchema<"blog">
+},
+},
+
 	};
 
-	type ContentConfig = typeof import('./config');
+	type ContentConfig = typeof import("./config");
 }

packages/astro/src/@types/astro.ts

@@ -1464,10 +1464,6 @@ export interface SSRResult {
 	_metadata: SSRMetadata;
 }
 
-export type MarkdownAstroData = {
-	frontmatter: MD['frontmatter'];
-};
-
 /* Preview server stuff */
 export interface PreviewServer {
 	host?: string;

packages/astro/src/content/internal.ts

@@ -137,12 +137,9 @@ async function render({
 		propagation: 'self',
 	});
 
-	if (!mod._internal && id.endsWith('.mdx')) {
-		throw new Error(`[Content] Failed to render MDX entry. Try installing @astrojs/mdx@latest`);
-	}
 	return {
 		Content,
 		headings: mod.getHeadings(),
-		injectedFrontmatter: mod._internal.injectedFrontmatter,
+		remarkPluginFrontmatter: mod.frontmatter,
 	};
 }

packages/astro/src/content/template/types.generated.d.ts

@@ -37,7 +37,7 @@ declare module 'astro:content' {
 		render(): Promise<{
 			Content: import('astro').MarkdownInstance<{}>['Content'];
 			headings: import('astro').MarkdownHeading[];
-			injectedFrontmatter: Record<string, any>;
+			remarkPluginFrontmatter: Record<string, any>;
 		}>;
 	};
 

packages/astro/src/content/vite-plugin-content-assets.ts

@@ -34,7 +34,7 @@ export function astroDelayedAssetPlugin({ mode }: { mode: string }): Plugin {
 			if (isDelayedAsset(id)) {
 				const basePath = id.split('?')[0];
 				const code = `
-					export { Content, getHeadings, _internal } from ${JSON.stringify(basePath)};
+					export { Content, getHeadings } from ${JSON.stringify(basePath)};
 					export const collectedLinks = ${JSON.stringify(LINKS_PLACEHOLDER)};
 					export const collectedStyles = ${JSON.stringify(STYLES_PLACEHOLDER)};
 				`;

packages/astro/src/core/errors/errors-data.ts

@@ -520,6 +520,20 @@ See https://docs.astro.build/en/guides/server-side-rendering/ for more informati
 		},
 		hint: 'See https://docs.astro.build/en/guides/content-collections/ for more information on content schemas.',
 	},
+	/**
+	 * @docs
+	 * @see
+	 * - [Frontmatter injection](https://docs.astro.build/en/guides/markdown-content/#example-injecting-frontmatter)
+	 * @description
+	 * A remark or rehype plugin attempted to inject invalid frontmatter. This occurs when "astro.frontmatter" is set to `null`, `undefined`, or an invalid JSON object.
+	 */
+	InvalidFrontmatterInjectionError: {
+		title: 'Invalid frontmatter injection.',
+		code: 6003,
+		message:
+			'A remark or rehype plugin attempted to inject invalid frontmatter. Ensure "astro.frontmatter" is set to a valid JSON object that is not `null` or `undefined`.',
+		hint: 'See the frontmatter injection docs https://docs.astro.build/en/guides/markdown-content/#example-injecting-frontmatter for more information.',
+	},
 	// Config Errors - 7xxx
 	UnknownConfigError: {
 		title: 'Unknown configuration error.',

packages/astro/src/vite-plugin-markdown/index.ts

@@ -1,21 +1,21 @@
 import { renderMarkdown } from '@astrojs/markdown-remark';
+import {
+	safelyGetAstroData,
+	InvalidAstroDataError,
+} from '@astrojs/markdown-remark/dist/internal.js';
 import fs from 'fs';
 import matter from 'gray-matter';
 import { fileURLToPath } from 'node:url';
 import type { Plugin } from 'vite';
 import { normalizePath } from 'vite';
 import type { AstroSettings } from '../@types/astro';
 import { getContentPaths } from '../content/index.js';
-import { AstroErrorData, MarkdownError } from '../core/errors/index.js';
+import { AstroError, AstroErrorData, MarkdownError } from '../core/errors/index.js';
 import type { LogOptions } from '../core/logger/core.js';
 import { warn } from '../core/logger/core.js';
 import { isMarkdownFile } from '../core/util.js';
 import type { PluginMetadata } from '../vite-plugin-astro/types.js';
-import {
-	escapeViteEnvReferences,
-	getFileInfo,
-	safelyGetAstroData,
-} from '../vite-plugin-utils/index.js';
+import { escapeViteEnvReferences, getFileInfo } from '../vite-plugin-utils/index.js';
 
 interface AstroPluginOptions {
 	settings: AstroSettings;
@@ -74,16 +74,17 @@ export default function markdown({ settings, logging }: AstroPluginOptions): Plu
 					isAstroFlavoredMd: false,
 					isExperimentalContentCollections: settings.config.experimental.contentCollections,
 					contentDir: getContentPaths(settings.config).contentDir,
-				} as any);
+					frontmatter: raw.data,
+				});
 
 				const html = renderResult.code;
 				const { headings } = renderResult.metadata;
-				const { frontmatter: injectedFrontmatter } = safelyGetAstroData(renderResult.vfile.data);
-				const frontmatter = {
-					...injectedFrontmatter,
-					...raw.data,
-				} as any;
+				const astroData = safelyGetAstroData(renderResult.vfile.data);
+				if (astroData instanceof InvalidAstroDataError) {
+					throw new AstroError(AstroErrorData.InvalidFrontmatterInjectionError);
+				}
 
+				const { frontmatter } = astroData;
 				const { layout } = frontmatter;
 
 				if (frontmatter.setup) {
@@ -100,9 +101,6 @@ export default function markdown({ settings, logging }: AstroPluginOptions): Plu
 
 				const html = ${JSON.stringify(html)};
 
-				export const _internal = {
-					injectedFrontmatter: ${JSON.stringify(injectedFrontmatter)},
-				}
 				export const frontmatter = ${JSON.stringify(frontmatter)};
 				export const file = ${JSON.stringify(fileId)};
 				export const url = ${JSON.stringify(fileUrl)};

packages/astro/src/vite-plugin-utils/index.ts

@@ -1,6 +1,5 @@
 import ancestor from 'common-ancestor-path';
-import type { Data } from 'vfile';
-import type { AstroConfig, MarkdownAstroData } from '../@types/astro';
+import type { AstroConfig } from '../@types/astro';
 import {
 	appendExtension,
 	appendForwardSlash,
@@ -36,33 +35,6 @@ export function getFileInfo(id: string, config: AstroConfig) {
 	return { fileId, fileUrl };
 }
 
-function isValidAstroData(obj: unknown): obj is MarkdownAstroData {
-	if (typeof obj === 'object' && obj !== null && obj.hasOwnProperty('frontmatter')) {
-		const { frontmatter } = obj as any;
-		try {
-			// ensure frontmatter is JSON-serializable
-			JSON.stringify(frontmatter);
-		} catch {
-			return false;
-		}
-		return typeof frontmatter === 'object' && frontmatter !== null;
-	}
-	return false;
-}
-
-export function safelyGetAstroData(vfileData: Data): MarkdownAstroData {
-	const { astro } = vfileData;
-
-	if (!astro) return { frontmatter: {} };
-	if (!isValidAstroData(astro)) {
-		throw Error(
-			`[Markdown] A remark or rehype plugin tried to add invalid frontmatter. Ensure "astro.frontmatter" is a JSON object!`
-		);
-	}
-
-	return astro;
-}
-
 /**
  * Normalizes different file names like:
  *

packages/astro/test/astro-markdown-frontmatter-injection.test.js

@@ -32,13 +32,10 @@ describe('Astro Markdown - frontmatter injection', () => {
 		}
 	});
 
-	it('overrides injected frontmatter with user frontmatter', async () => {
+	it('allow user frontmatter mutation', async () => {
 		const frontmatterByPage = JSON.parse(await fixture.readFile('/glob.json'));
-		const readingTimes = frontmatterByPage.map(
-			(frontmatter = {}) => frontmatter.injectedReadingTime?.text
-		);
-		const titles = frontmatterByPage.map((frontmatter = {}) => frontmatter.title);
-		expect(titles).to.contain('Overridden title');
-		expect(readingTimes).to.contain('1000 min read');
+		const descriptions = frontmatterByPage.map((frontmatter = {}) => frontmatter.description);
+		expect(descriptions).to.contain('Processed by remarkDescription plugin: Page 1 description');
+		expect(descriptions).to.contain('Processed by remarkDescription plugin: Page 2 description');
 	});
 });

packages/astro/test/fixtures/astro-markdown-frontmatter-injection/astro.config.mjs

@@ -1,11 +1,11 @@
 import { defineConfig } from 'astro/config';
-import { rehypeReadingTime, remarkTitle } from './src/markdown-plugins.mjs'
+import { rehypeReadingTime, remarkTitle, remarkDescription } from './src/markdown-plugins.mjs'
 
 // https://astro.build/config
 export default defineConfig({
   site: 'https://astro.build/',
 	markdown: {
-		remarkPlugins: [remarkTitle],
+		remarkPlugins: [remarkTitle, remarkDescription],
 		rehypePlugins: [rehypeReadingTime],
 	}
 });

packages/astro/test/fixtures/astro-markdown-frontmatter-injection/src/markdown-plugins.mjs

@@ -18,3 +18,9 @@ export function remarkTitle() {
 		});
 	};
 }
+
+export function remarkDescription() {
+	return function (tree, { data }) {
+		data.astro.frontmatter.description = `Processed by remarkDescription plugin: ${data.astro.frontmatter.description}`
+	};
+}

packages/astro/test/fixtures/astro-markdown-frontmatter-injection/src/pages/page-1.md

@@ -1,3 +1,7 @@
+---
+description: 'Page 1 description'
+---
+
 # Page 1
 
 Look at that!

packages/astro/test/fixtures/astro-markdown-frontmatter-injection/src/pages/page-2.md

@@ -1,3 +1,7 @@
+---
+description: 'Page 2 description'
+---
+
 # Page 2
 
 ## Table of contents