[Content] Throw on relative image usage (#5648)

* chore: add rel image error plugin

* deps: mdast, mdast types

* chore: add rel image throw to mdx

* refactor: doc rel image path plugin

* fix: respect experimental flag in md remark

* chore: changeset

* deps: remove mdast package

* fix: resolve contentDir from config

* fix: apply MDX plugin after user plugins

* fix: stub out contentDir

15 files changed, 151 insertions, 2 deletions

diff --git a/.changeset/khaki-crabs-develop.md b/.changeset/khaki-crabs-develop.md
new file mode 100644
index 000000000..b42001b6e
--- /dev/null
+++ b/.changeset/khaki-crabs-develop.md
@@ -0,0 +1,7 @@
+---
+'astro': patch
+'@astrojs/mdx': patch
+'@astrojs/markdown-remark': patch
+---
+
+Prevent relative image paths in `src/content/`
diff --git a/packages/astro/src/content/index.ts b/packages/astro/src/content/index.ts
index 7fc96be29..5c3e6defe 100644
--- a/packages/astro/src/content/index.ts
+++ b/packages/astro/src/content/index.ts
@@ -4,3 +4,4 @@ export {
 } from './vite-plugin-content-assets.js';
 export { astroContentServerPlugin } from './vite-plugin-content-server.js';
 export { astroContentVirtualModPlugin } from './vite-plugin-content-virtual-mod.js';
+export { getContentPaths } from './utils.js';
diff --git a/packages/astro/src/core/build/generate.ts b/packages/astro/src/core/build/generate.ts
index a20b33e18..11dfb1788 100644
--- a/packages/astro/src/core/build/generate.ts
+++ b/packages/astro/src/core/build/generate.ts
@@ -12,6 +12,7 @@ import type {
 	RouteType,
 	SSRLoadedRenderer,
 } from '../../@types/astro';
+import { getContentPaths } from '../../content/index.js';
 import { BuildInternals, hasPrerenderedPages } from '../../core/build/internal.js';
 import {
 	prependForwardSlash,
@@ -352,6 +353,8 @@ async function generatePath(
 		markdown: {
 			...settings.config.markdown,
 			isAstroFlavoredMd: settings.config.legacy.astroFlavoredMarkdown,
+			isExperimentalContentCollections: settings.config.experimental.contentCollections,
+			contentDir: getContentPaths(settings.config).contentDir,
 		},
 		mode: opts.mode,
 		renderers,
diff --git a/packages/astro/src/core/build/vite-plugin-ssr.ts b/packages/astro/src/core/build/vite-plugin-ssr.ts
index 71a3b513a..dbe5b1b4c 100644
--- a/packages/astro/src/core/build/vite-plugin-ssr.ts
+++ b/packages/astro/src/core/build/vite-plugin-ssr.ts
@@ -15,6 +15,7 @@ import { serializeRouteData } from '../routing/index.js';
 import { addRollupInput } from './add-rollup-input.js';
 import { getOutFile, getOutFolder } from './common.js';
 import { eachPrerenderedPageData, eachServerPageData, sortedCSS } from './internal.js';
+import { getContentPaths } from '../../content/index.js';
 
 export const virtualModuleId = '@astrojs-ssr-virtual-entry';
 const resolvedVirtualModuleId = '\0' + virtualModuleId;
@@ -208,6 +209,8 @@ function buildManifest(
 		markdown: {
 			...settings.config.markdown,
 			isAstroFlavoredMd: settings.config.legacy.astroFlavoredMarkdown,
+			isExperimentalContentCollections: settings.config.experimental.contentCollections,
+			contentDir: getContentPaths(settings.config).contentDir,
 		},
 		pageMap: null as any,
 		renderers: [],
diff --git a/packages/astro/src/core/render/dev/environment.ts b/packages/astro/src/core/render/dev/environment.ts
index 5c4a8ed73..1fabf486d 100644
--- a/packages/astro/src/core/render/dev/environment.ts
+++ b/packages/astro/src/core/render/dev/environment.ts
@@ -1,4 +1,5 @@
 import type { AstroSettings, RuntimeMode } from '../../../@types/astro';
+import { getContentPaths } from '../../../content/index.js';
 import type { LogOptions } from '../../logger/core.js';
 import type { ModuleLoader } from '../../module-loader/index';
 import type { Environment } from '../index';
@@ -24,6 +25,8 @@ export function createDevelopmentEnvironment(
 		markdown: {
 			...settings.config.markdown,
 			isAstroFlavoredMd: settings.config.legacy.astroFlavoredMarkdown,
+			isExperimentalContentCollections: settings.config.experimental.contentCollections,
+			contentDir: getContentPaths(settings.config).contentDir,
 		},
 		mode,
 		// This will be overridden in the dev server
diff --git a/packages/astro/src/core/render/environment.ts b/packages/astro/src/core/render/environment.ts
index 8746df5f1..edf3cc0e6 100644
--- a/packages/astro/src/core/render/environment.ts
+++ b/packages/astro/src/core/render/environment.ts
@@ -37,7 +37,11 @@ export function createBasicEnvironment(options: CreateBasicEnvironmentArgs): Env
 	const mode = options.mode ?? 'development';
 	return createEnvironment({
 		...options,
-		markdown: options.markdown ?? {},
+		markdown: {
+			...(options.markdown ?? {}),
+			// Stub out, not important for basic rendering
+			contentDir: new URL('file:///src/content/'),
+		},
 		mode,
 		renderers: options.renderers ?? [],
 		resolve: options.resolve ?? ((s: string) => Promise.resolve(s)),
diff --git a/packages/astro/src/vite-plugin-markdown-legacy/index.ts b/packages/astro/src/vite-plugin-markdown-legacy/index.ts
index b72418bdb..5203a2b3f 100644
--- a/packages/astro/src/vite-plugin-markdown-legacy/index.ts
+++ b/packages/astro/src/vite-plugin-markdown-legacy/index.ts
@@ -4,6 +4,7 @@ import matter from 'gray-matter';
 import { fileURLToPath } from 'url';
 import { Plugin, ResolvedConfig, transformWithEsbuild } from 'vite';
 import type { AstroSettings } from '../@types/astro';
+import { getContentPaths } from '../content/index.js';
 import { pagesVirtualModuleId } from '../core/app/index.js';
 import { cachedCompilation, CompileProps } from '../core/compile/index.js';
 import { AstroErrorData, MarkdownError } from '../core/errors/index.js';
@@ -162,6 +163,8 @@ export default function markdown({ settings }: AstroPluginOptions): Plugin {
 					...renderOpts,
 					fileURL: fileUrl,
 					isAstroFlavoredMd: true,
+					isExperimentalContentCollections: settings.config.experimental.contentCollections,
+					contentDir: getContentPaths(settings.config).contentDir,
 				} as any);
 				let { code: astroResult, metadata } = renderResult;
 				const { layout = '', components = '', setup = '', ...content } = frontmatter;
diff --git a/packages/astro/src/vite-plugin-markdown/index.ts b/packages/astro/src/vite-plugin-markdown/index.ts
index 66955dca5..67ad4c1e0 100644
--- a/packages/astro/src/vite-plugin-markdown/index.ts
+++ b/packages/astro/src/vite-plugin-markdown/index.ts
@@ -5,6 +5,7 @@ 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 type { LogOptions } from '../core/logger/core.js';
 import { warn } from '../core/logger/core.js';
@@ -71,6 +72,8 @@ export default function markdown({ settings, logging }: AstroPluginOptions): Plu
 					...settings.config.markdown,
 					fileURL: new URL(`file://${fileId}`),
 					isAstroFlavoredMd: false,
+					isExperimentalContentCollections: settings.config.experimental.contentCollections,
+					contentDir: getContentPaths(settings.config).contentDir,
 				} as any);
 
 				const html = renderResult.code;
diff --git a/packages/integrations/mdx/package.json b/packages/integrations/mdx/package.json
index 08a681097..e2ae2521f 100644
--- a/packages/integrations/mdx/package.json
+++ b/packages/integrations/mdx/package.json
@@ -52,6 +52,7 @@
     "@types/chai": "^4.3.1",
     "@types/estree": "^1.0.0",
     "@types/github-slugger": "^1.3.0",
+    "@types/mdast": "^3.0.10",
     "@types/mocha": "^9.1.1",
     "@types/yargs-parser": "^21.0.0",
     "astro": "workspace:*",
diff --git a/packages/integrations/mdx/src/plugins.ts b/packages/integrations/mdx/src/plugins.ts
index d46ab6cd4..a93db383b 100644
--- a/packages/integrations/mdx/src/plugins.ts
+++ b/packages/integrations/mdx/src/plugins.ts
@@ -1,9 +1,11 @@
 import { rehypeHeadingIds } from '@astrojs/markdown-remark';
+import type { Image } from 'mdast';
 import { nodeTypes } from '@mdx-js/mdx';
 import type { PluggableList } from '@mdx-js/mdx/lib/core.js';
 import type { Options as MdxRollupPluginOptions } from '@mdx-js/rollup';
 import type { AstroConfig, MarkdownAstroData } from 'astro';
 import type { Literal, MemberExpression } from 'estree';
+import { visit } from 'unist-util-visit';
 import { visit as estreeVisit } from 'estree-util-visit';
 import { bold, yellow } from 'kleur/colors';
 import rehypeRaw from 'rehype-raw';
@@ -15,7 +17,8 @@ import { rehypeInjectHeadingsExport } from './rehype-collect-headings.js';
 import rehypeMetaString from './rehype-meta-string.js';
 import remarkPrism from './remark-prism.js';
 import remarkShiki from './remark-shiki.js';
-import { jsToTreeNode } from './utils.js';
+import { jsToTreeNode, isRelativePath } from './utils.js';
+import { pathToFileURL } from 'node:url';
 
 export function recmaInjectImportMetaEnvPlugin({
 	importMetaEnv,
@@ -113,6 +116,34 @@ export function rehypeApplyFrontmatterExport(pageFrontmatter: Record<string, any
 	};
 }
 
+/**
+ * `src/content/` does not support relative image paths.
+ * This plugin throws an error if any are found
+ */
+function toRemarkContentRelImageError({ srcDir }: { srcDir: URL }) {
+	const contentDir = new URL('content/', srcDir);
+	return function remarkContentRelImageError() {
+		return (tree: any, vfile: VFile) => {
+			const isContentFile = pathToFileURL(vfile.path).href.startsWith(contentDir.href);
+			if (!isContentFile) return;
+
+			const relImagePaths = new Set<string>();
+			visit(tree, 'image', function raiseError(node: Image) {
+				if (isRelativePath(node.url)) {
+					relImagePaths.add(node.url);
+				}
+			});
+			if (relImagePaths.size === 0) return;
+
+			const errorMessage =
+				`Relative image paths are not supported in the content/ directory. Place local images in the public/ directory and use absolute paths (see https://docs.astro.build/en/guides/images/#in-markdown-files):\n` +
+				[...relImagePaths].map((path) => JSON.stringify(path)).join(',\n');
+
+			throw new Error(errorMessage);
+		};
+	};
+}
+
 const DEFAULT_REMARK_PLUGINS: PluggableList = [remarkGfm, remarkSmartypants];
 const DEFAULT_REHYPE_PLUGINS: PluggableList = [];
 
@@ -146,6 +177,11 @@ export async function getRemarkPlugins(
 	}
 
 	remarkPlugins = [...remarkPlugins, ...(mdxOptions.remarkPlugins ?? [])];
+
+	// Apply last in case user plugins resolve relative image paths
+	if (config.experimental.contentCollections) {
+		remarkPlugins.push(toRemarkContentRelImageError(config));
+	}
 	return remarkPlugins;
 }
 
diff --git a/packages/integrations/mdx/src/utils.ts b/packages/integrations/mdx/src/utils.ts
index 60a50c85a..e803dc300 100644
--- a/packages/integrations/mdx/src/utils.ts
+++ b/packages/integrations/mdx/src/utils.ts
@@ -95,3 +95,22 @@ export function handleExtendsNotSupported(pluginConfig: any) {
 		);
 	}
 }
+
+// Following utils taken from `packages/astro/src/core/path.ts`:
+
+export function isRelativePath(path: string) {
+	return startsWithDotDotSlash(path) || startsWithDotSlash(path);
+}
+
+function startsWithDotDotSlash(path: string) {
+	const c1 = path[0];
+	const c2 = path[1];
+	const c3 = path[2];
+	return c1 === '.' && c2 === '.' && c3 === '/';
+}
+
+function startsWithDotSlash(path: string) {
+	const c1 = path[0];
+	const c2 = path[1];
+	return c1 === '.' && c2 === '/';
+}
diff --git a/packages/markdown/remark/src/index.ts b/packages/markdown/remark/src/index.ts
index 6d69bcd20..07df39ee8 100644
--- a/packages/markdown/remark/src/index.ts
+++ b/packages/markdown/remark/src/index.ts
@@ -14,6 +14,7 @@ import remarkPrism from './remark-prism.js';
 import scopedStyles from './remark-scoped-styles.js';
 import remarkShiki from './remark-shiki.js';
 import remarkUnwrap from './remark-unwrap.js';
+import toRemarkContentRelImageError from './remark-content-rel-image-error.js';
 
 import rehypeRaw from 'rehype-raw';
 import rehypeStringify from 'rehype-stringify';
@@ -42,6 +43,8 @@ export async function renderMarkdown(
 		remarkRehype = {},
 		extendDefaultPlugins = false,
 		isAstroFlavoredMd = false,
+		isExperimentalContentCollections = false,
+		contentDir,
 	} = opts;
 	const input = new VFile({ value: content, path: fileURL });
 	const scopedClassName = opts.$?.scopedClassName;
@@ -73,6 +76,11 @@ export async function renderMarkdown(
 		parser.use([remarkPrism(scopedClassName)]);
 	}
 
+	// Apply later in case user plugins resolve relative image paths
+	if (isExperimentalContentCollections) {
+		parser.use([toRemarkContentRelImageError({ contentDir })]);
+	}
+
 	parser.use([
 		[
 			markdownToHtml as any,
diff --git a/packages/markdown/remark/src/remark-content-rel-image-error.ts b/packages/markdown/remark/src/remark-content-rel-image-error.ts
new file mode 100644
index 000000000..0704ebdd1
--- /dev/null
+++ b/packages/markdown/remark/src/remark-content-rel-image-error.ts
@@ -0,0 +1,52 @@
+import type { Image } from 'mdast';
+import { visit } from 'unist-util-visit';
+import { pathToFileURL } from 'url';
+import type { VFile } from 'vfile';
+
+/**
+ * `src/content/` does not support relative image paths.
+ * This plugin throws an error if any are found
+ */
+export default function toRemarkContentRelImageError({ contentDir }: { contentDir: URL }) {
+	return function remarkContentRelImageError() {
+		return (tree: any, vfile: VFile) => {
+			const isContentFile = pathToFileURL(vfile.path).href.startsWith(contentDir.href);
+			if (!isContentFile) return;
+
+			const relImagePaths = new Set<string>();
+			visit(tree, 'image', function raiseError(node: Image) {
+				console.log(node.url);
+				if (isRelativePath(node.url)) {
+					relImagePaths.add(node.url);
+				}
+			});
+			if (relImagePaths.size === 0) return;
+
+			const errorMessage =
+				`Relative image paths are not supported in the content/ directory. Place local images in the public/ directory and use absolute paths (see https://docs.astro.build/en/guides/images/#in-markdown-files)\n` +
+				[...relImagePaths].map((path) => JSON.stringify(path)).join(',\n');
+
+			// Throw raw string to use `astro:markdown` default formatting
+			throw errorMessage;
+		};
+	};
+}
+
+// Following utils taken from `packages/astro/src/core/path.ts`:
+
+function isRelativePath(path: string) {
+	return startsWithDotDotSlash(path) || startsWithDotSlash(path);
+}
+
+function startsWithDotDotSlash(path: string) {
+	const c1 = path[0];
+	const c2 = path[1];
+	const c3 = path[2];
+	return c1 === '.' && c2 === '.' && c3 === '/';
+}
+
+function startsWithDotSlash(path: string) {
+	const c1 = path[0];
+	const c2 = path[1];
+	return c1 === '.' && c2 === '/';
+}
diff --git a/packages/markdown/remark/src/types.ts b/packages/markdown/remark/src/types.ts
index 76dfe9b73..15465d950 100644
--- a/packages/markdown/remark/src/types.ts
+++ b/packages/markdown/remark/src/types.ts
@@ -54,6 +54,10 @@ export interface MarkdownRenderingOptions extends AstroMarkdownOptions {
 		scopedClassName: string | null;
 	};
 	isAstroFlavoredMd?: boolean;
+	/** Used to prevent relative image imports from `src/content/` */
+	isExperimentalContentCollections?: boolean;
+	/** Used to prevent relative image imports from `src/content/` */
+	contentDir: URL;
 }
 
 export interface MarkdownHeading {
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 9abcaf0a3..8fd5d9273 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -2889,6 +2889,7 @@ importers:
       '@types/chai': ^4.3.1
       '@types/estree': ^1.0.0
       '@types/github-slugger': ^1.3.0
+      '@types/mdast': ^3.0.10
       '@types/mocha': ^9.1.1
       '@types/yargs-parser': ^21.0.0
       acorn: ^8.8.0
@@ -2940,6 +2941,7 @@ importers:
       '@types/chai': 4.3.4
       '@types/estree': 1.0.0
       '@types/github-slugger': 1.3.0
+      '@types/mdast': 3.0.10
       '@types/mocha': 9.1.1
       '@types/yargs-parser': 21.0.0
       astro: link:../../astro