Improve MDX setup (#2265)

This fixes a couple of things.
- The argument was removed from `useMDXComponents()`. In reality this
function doesn’t receive any arguments.
- Components overrides are defined outside of `useMDXComponents()`.
`useMDXComponents()` is called during render. Defining React components
during render causes unnecessary re-renders and loss of state.
- The `**/*.mdx` glob is included in the `tsconfig.json` include
patterns. This makes `.mdx` files part of the same TypeScript program in
the editor. This leads to a better editor experience and reduced memory
and CPU usage.
- This augments the `mdx/types` module to define the `JSX` namespace.
React 18 defined the global `JSX` namespace. React 19 no longer does
this. This leads to type errors in `mdx/types` resulting unresolved
`any` types. This augmentation makes the MDX types understand React.

Author: remcohaszing

src/mdx-components.tsx

@@ -1,8 +1,18 @@
 import type { MDXComponents } from "mdx/types";
-import React, { ReactNode } from "react";
+import React from "react";
 import { CodeExample } from "./components/code-example";
 import Link from "next/link";
 
+declare module "mdx/types" {
+  // Augment the MDX types to make it understand React.
+  namespace JSX {
+    type Element = React.JSX.Element;
+    type ElementClass = React.JSX.ElementClass;
+    type ElementType = React.JSX.ElementType;
+    type IntrinsicElements = React.JSX.IntrinsicElements;
+  }
+}
+
 function getTextContent(node: React.ReactNode): string {
   if (typeof node === "string" || typeof node === "number") {
     return String(node);
@@ -51,64 +61,70 @@ function createHeading(level: 1 | 2 | 3 | 4 | 5 | 6) {
   };
 }
 
+const components = {
+  // Allows customizing built-in components, e.g. to add styling.
+  // h1: ({ children }) => <h1 style={{ fontSize: "100px" }}>{children}</h1>,
+
+  h2: createHeading(2),
+  h3: createHeading(3),
+  h4: createHeading(4),
+  h5: createHeading(5),
+  h6: createHeading(6),
+
+  a(props) {
+    return <Link {...(props as React.ComponentProps<typeof Link>)} />;
+  },
+
+  code({ children }) {
+    if (typeof children !== "string") {
+      return <code>{children}</code>;
+    }
+
+    if (children.startsWith("<")) {
+      return <code>{children}</code>;
+    }
+
+    return (
+      <code>
+        {children
+          .split(/(<[^>]+>)/g)
+          .map((part, i) => (part.startsWith("<") && part.endsWith(">") ? <var key={i}>{part}</var> : part))}
+      </code>
+    );
+  },
+
+  pre(props) {
+    let child = React.Children.only(props.children) as React.ReactElement;
+    if (!child) return null;
+
+    // @ts-ignore
+    let { className, children: code } = child.props;
+    let lang = className ? className.replace("language-", "") : "";
+    let filename = undefined;
+
+    // Extract `[!code filename:…]` directives from the first line of code
+    let lines = code.split("\n");
+    let filenameRegex = /\[\!code filename\:(.+)\]/;
+    let match = lines[0].match(filenameRegex);
+    if (match) {
+      filename = match[1];
+      code = lines.splice(1).join("\n");
+    }
+
+    return (
+      <div>
+        <CodeExample example={{ lang, code }} className="not-prose" filename={filename} />
+      </div>
+    );
+  },
+} satisfies MDXComponents;
+
+declare global {
+  // Provide type-safety of provided components inside MDX files.
+  type MDXProvidedComponents = typeof components;
+}
+
 // This file is required to use MDX in `app` directory.
-export function useMDXComponents(components: MDXComponents): MDXComponents {
-  return {
-    // Allows customizing built-in components, e.g. to add styling.
-    // h1: ({ children }) => <h1 style={{ fontSize: "100px" }}>{children}</h1>,
-    ...components,
-
-    h2: createHeading(2),
-    h3: createHeading(3),
-    h4: createHeading(4),
-    h5: createHeading(5),
-    h6: createHeading(6),
-
-    a(props: any) {
-      return <Link {...props} />;
-    },
-
-    code({ children }: { children: string | ReactNode }) {
-      if (typeof children !== "string") {
-        return <code>{children}</code>;
-      }
-
-      if (children.startsWith("<")) {
-        return <code>{children}</code>;
-      }
-
-      return (
-        <code>
-          {children
-            .split(/(<[^>]+>)/g)
-            .map((part, i) => (part.startsWith("<") && part.endsWith(">") ? <var key={i}>{part}</var> : part))}
-        </code>
-      );
-    },
-
-    pre(props) {
-      let child = React.Children.only(props.children) as React.ReactElement;
-      if (!child) return null;
-
-      // @ts-ignore
-      let { className, children: code } = child.props;
-      let lang = className ? className.replace("language-", "") : "";
-      let filename = undefined;
-
-      // Extract `[!code filename:…]` directives from the first line of code
-      let lines = code.split("\n");
-      let filenameRegex = /\[\!code filename\:(.+)\]/;
-      let match = lines[0].match(filenameRegex);
-      if (match) {
-        filename = match[1];
-        code = lines.splice(1).join("\n");
-      }
-
-      return (
-        <div>
-          <CodeExample example={{ lang, code }} className="not-prose" filename={filename} />
-        </div>
-      );
-    },
-  };
+export function useMDXComponents(): MDXProvidedComponents {
+  return components;
 }

tsconfig.json

@@ -22,6 +22,6 @@
       "@/*": ["./src/*"]
     }
   },
-  "include": ["next-env.d.ts", "**/*.ts", "**/*.tsx", ".next/types/**/*.ts"],
+  "include": ["next-env.d.ts", "**/*.mdx", "**/*.ts", "**/*.tsx", ".next/types/**/*.ts"],
   "exclude": ["node_modules"]
 }