# Layout that imports components for you instead of each individual MDX file

Using Astro, I have a layout file: /src/layouts/MdxLayout.astro where I try to set allowed components Button and Link to be rendered if passed in from a page file.

---
import BaseLayout from '@/layouts/Base/BaseLayout.astro';
import Button from '@/components/Button/Button';
import Link from "@/components/Link/Link";
---

<BaseLayout components={{ Button: Button, Link: Link }}>
  <slot />
</BaseLayout>

Hoping this would work in /src/pages/mdx.mdx:

---
layout: '@/layouts/MdxLayout.astro'
title: "Hello, World!"
---

# Lorem ipsum

<Button>Click me</Button>

So I will not have to add imports to all mdx files where I wish to use these components, (ie: import Button from '@/components/Button/Button'). Without this import though, I am faced with the error:

Expected component Button to be defined: you likely forgot to import, pass, or provide it.

My question: is there any way to predefine components in a layout file that can then be used in a mdx file that uses this layout without having to import them in the mdx file?

## Answer 1

It is possible but not natively. You have three options:

1. use a custom Remark or Rehype plugin
2. use an existing library that offers this functionality
3. map existing HTML tags to custom components

### Using Remark or Rehype

You can create a custom Remark/Rehype plugin to update the tree with the import statements for your components. Something like:

import type { Root } from 'hast';
import type { Plugin as UnifiedPlugin } from 'unified';
import { visit } from 'unist-util-visit';

export const rehypeAutoImportComponents: UnifiedPlugin<[], Root> =
  () => (tree, file) => {
    const importsStatements = [];

    visit(tree, 'mdxJsxFlowElement', (node, index, nodeParent) => {
      if (node.name === 'Button') importsStatements.push('import Button from "@/components/Button/Button"');
    });

    tree.children.unshift(...importsStatements);
  };

You'll need to figure out how to resolve your path aliases and how to avoid duplicated import statements.

Then update your Astro configuration file:

import { rehypeAutoImportComponents } from './src/utils/rehype-auto-import-components';

export default defineConfig({
  markdown: {
    rehypePlugins: [
      rehypeAutoImportComponents
    ],
  },
});

You can also add an option to your plugin to pass the components directly in your Astro config file instead of hardcoding them in your plugin.

Note: with this solution, you can remove the components property in <BaseLayout ... />.

### Existing libraries

I haven't test them but you can look for astro-auto-import or Astro-M²DX for example.

### Mapping HTML tags to custom components

Another alternative is to map HTML tags to custom components:

---
import BaseLayout from '@/layouts/Base/BaseLayout.astro';
import Button from '@/components/Button/Button';
import Link from "@/components/Link/Link";
---

<BaseLayout components={{ a: Link, button: Button }}>
  <slot />
</BaseLayout>
However to be able to map HTML tags (ie. <button />) you need a plugin to disable the default behavior of MDXJS (ignoring HTML tags). Something like:

import type { Root } from 'hast';
import type { Plugin as UnifiedPlugin } from 'unified';
import { visit } from 'unist-util-visit';

export const rehypeDisableExplicitJsx: UnifiedPlugin<[], Root> =
  () => (tree) => {
    visit(tree, ['mdxJsxFlowElement', 'mdxJsxTextElement'], (node) => {
      if (node.data && '_mdxExplicitJsx' in node.data) {
        delete node.data._mdxExplicitJsx;
      }
    });
  };

Then you can add this plugin to your Astro config:

import { rehypeDisableExplicitJsx } from './src/utils/rehype-disable-explicit-jsx';

export default defineConfig({
  markdown: {
    rehypePlugins: [
      rehypeDisableExplicitJsx
    ],
  },
});

With this, your MDX file can look like this:

---
layout: '@/layouts/MdxLayout.astro'
title: "Hello, World!"
---

# Lorem ipsum

<button>Click me</button>

The caveat is that for more complex components (when a HTML tag does not exist for it) you'll need extra logic. You could map a div to a custom component where you check for a particular class/attribute to return the right component.

## Answer 2

Thanks to Armand's answer, I made it work with this rehype plugin:

import { parse, resolve } from 'node:path';

import { parse as parseJs } from 'acorn';
import type { VFile } from 'vfile';

const resolveModulePath = (path: string) => {
  // Resolve relative paths
  if (path.startsWith('.')) return resolve(path);
  // Don’t resolve other paths (e.g. npm modules)
  return path;
};

type NamedImportConfig = string | [from: string, as: string];
type ImportsConfig = (string | Record<string, string | NamedImportConfig[]>)[];

/**
 * Use a filename to generate a default import name.
 * @example
 * getDefaultImportName('/path/to/cool-component.astro');
 * // => coolcomponent
 */
function getDefaultImportName(path: string): string {
  return parse(path).name.replaceAll(/[^\w\d]/g, '');
}

/**
 * Create an import statement.
 * @param imported Stuff to import (e.g. `Thing` or `{ Named }`)
 * @param module Module to import from (e.g. `module-thing`)
 */
function formatImport(imported: string, module: string): string {
  return `import ${imported} from ${JSON.stringify(module)};`;
}

/** Get the parts for a named import statement from config. */
function formatNamedImports(namedImport: NamedImportConfig[]): string {
  const imports: string[] = [];
  for (const imp of namedImport) {
    if (typeof imp === 'string') {
      imports.push(imp);
    } else {
      const [from, as] = imp;
      imports.push(`${from} as ${as}`);
    }
  }
  return `{ ${imports.join(', ')} }`;
}

/** Generate imports from a full imports config array. */
function processImportsConfig(config: ImportsConfig) {
  const imports = [];
  for (const option of config) {
    if (typeof option === 'string') {
      imports.push(formatImport(getDefaultImportName(option), resolveModulePath(option)));
    } else {
      for (const path in option) {
        const namedImportsOrNamespace = option[path];
        if (typeof namedImportsOrNamespace === 'string') {
          imports.push(formatImport(`* as ${namedImportsOrNamespace}`, resolveModulePath(path)));
        } else {
          const importString = formatNamedImports(namedImportsOrNamespace);
          imports.push(formatImport(importString, resolveModulePath(path)));
        }
      }
    }
  }
  return imports;
}

/** Get an MDX node representing a block of imports based on user config. */
function generateImportsNode(config: ImportsConfig) {
  const imports = processImportsConfig(config);
  const js = imports.join('\n');
  return {
    type: 'mdxjsEsm',
    value: '',
    data: {
      estree: {
        ...parseJs(js, { ecmaVersion: 'latest', sourceType: 'module' }),
        type: 'Program',
        sourceType: 'module',
      },
    },
  };
}

type MfxFile = VFile & { data?: { astro?: { frontmatter?: { layout?: string } } } };

type PluginConfig = {
  [layoutName: string]: string[];
};

export function AutoImportComponentsPerLayout(pluginConfig: PluginConfig) {
  return function (tree: { children: unknown[] }, vfile: MfxFile) {
    const fileLayout: string =
      vfile?.data?.astro?.frontmatter?.layout?.split('/').pop()?.split('.')[0] || '';

    if (!fileLayout) {
      return;
    }

    // for each key in PluginConfig loop and add the array of imports to the imports array
    for (const key in pluginConfig) {
      if (Object.prototype.hasOwnProperty.call(pluginConfig, key)) {
        if (key === fileLayout) {
          const imports: string[] = [];
          const components: string[] = pluginConfig[key];
          components.forEach((component: string) => {
            imports.push(`@/components/${component}/${component}.tsx`);
          });
          const importsNode = generateImportsNode(imports);
          tree?.children.unshift(importsNode);
        }
      }
    }
  };
}

Which can be used like so:

  integrations: [
    mdx({
      rehypePlugins: [[AutoImportComponentsPerLayout, { BaseLayout: ["Button", "Card"], AnotherLayout: ["Button"] }  ]]
    })
  ],