next.js/packages/eslint-plugin-next/src/rules/no-styled-jsx-in-document.ts

import { defineRule } from '../utils/define-rule'
import * as path from 'path'

const url = 'https://nextjs.org/docs/messages/no-styled-jsx-in-document'

export = defineRule({
  meta: {
    docs: {
      description: 'Prevent usage of `styled-jsx` in `pages/_document.js`.',
      recommended: true,
      url,
    },
    type: 'problem',
    schema: [],
  },
  create(context) {
    return {
      JSXOpeningElement(node) {
        const document = context.filename.split('pages', 2)[1]
        if (!document) {
          return
        }
        const { name, dir } = path.parse(document)

        if (
          !(
            name.startsWith('_document') ||
            (dir === '/_document' && name === 'index')
          )
        ) {
          return
        }

        if (
          node.name.name === 'style' &&
          node.attributes.find(
            (attr) => attr.type === 'JSXAttribute' && attr.name.name === 'jsx'
          )
        ) {
          context.report({
            node,
            message: `\`styled-jsx\` should not be used in \`pages/_document.js\`. See: ${url}`,
          })
        }
      },
    }
  },
})