require-theme-mermaid-when-markdown-mermaid-enabled

Require @docusaurus/theme-mermaid when markdown.mermaid is enabled.

Targeted pattern scope

This rule focuses on docusaurus.config.* files.

It reports config that enables:

• markdown.mermaid: true

without also enabling:

• @docusaurus/theme-mermaid

What this rule reports

This rule reports Mermaid markdown support that is enabled in config without the corresponding Mermaid theme being configured.

Why this rule exists

The Docusaurus Mermaid docs require both pieces together:

• add @docusaurus/theme-mermaid
• set markdown.mermaid to true

Enabling only the markdown flag leaves the site config in a misleading half-configured state.

Mermaid relationship diagram

❌ Incorrect

export default {
    markdown: {
        mermaid: true,
    },
};

✅ Correct

export default {
    themes: ["@docusaurus/theme-mermaid"],
    markdown: {
        mermaid: true,
    },
};

Behavior and migration notes

This rule provides a suggestion when it can safely add @docusaurus/theme-mermaid to an existing literal themes array or create a new top-level themes property.

Additional examples

❌ Incorrect — markdown enabled with unrelated themes only

export default {
    themes: ["@easyops-cn/docusaurus-search-local"],
    markdown: {
        mermaid: true,
    },
};

✅ Correct — Mermaid theme appended

export default {
    themes: [
        "@easyops-cn/docusaurus-search-local",
        "@docusaurus/theme-mermaid",
    ],
    markdown: {
        mermaid: true,
    },
};

ESLint flat config example

import docusaurus2 from "eslint-plugin-docusaurus-2";

export default [docusaurus2.configs.recommended];

When not to use it

Do not use this rule only if you intentionally stage Mermaid setup across multiple commits and do not want linting to require both sides of the config yet.

Rule catalog ID: R092

Further reading

• Docusaurus theme docs: @docusaurus/theme-mermaid