Unable to reference frontmatter fields inside MDX

Description

Documentation states https://www.gatsbyjs.org/docs/mdx/writing-pages/ that Frontmatter is also available in props.pageContext.frontmatter and can be accessed in blocks of JSX in your MDX document:

When I try to read my frontmatter inside mdx I get an error: Cannot read property 'frontmatter' of undefined

System: OS: macOS 10.15.2 CPU: (16) x64 Intel® Core™ i9-9980HK CPU @ 2.40GHz Shell: 5.7.1 - /bin/zsh Binaries: Node: 12.14.1 - /usr/local/bin/node npm: 6.13.4 - /usr/local/bin/npm Languages: Python: 2.7.16 - /usr/bin/python npmPackages: gatsby: ^2.15.15 => 2.15.15 gatsby-image: ^2.2.19 => 2.2.19 gatsby-plugin-alias-imports: ^1.0.5 => 1.0.5 gatsby-plugin-catch-links: ^2.1.9 => 2.1.9 gatsby-plugin-facebook-pixel: ^1.0.3 => 1.0.3 gatsby-plugin-google-analytics: ^2.1.16 => 2.1.16 gatsby-plugin-google-gtag: ^1.1.8 => 1.1.8 gatsby-plugin-mdx: ^1.0.41 => 1.0.41 gatsby-plugin-react-helmet: ^3.1.7 => 3.1.7 gatsby-plugin-sharp: ^2.2.22 => 2.2.22 gatsby-plugin-sitemap: ^2.2.12 => 2.2.12 gatsby-plugin-styled-components: ^3.1.5 => 3.1.5 gatsby-remark-autolink-headers: ^2.1.10 => 2.1.10 gatsby-remark-copy-linked-files: ^2.1.19 => 2.1.19 gatsby-remark-images: ^3.1.22 => 3.1.22 gatsby-source-filesystem: ^2.1.22 => 2.1.22 gatsby-transformer-json: ^2.2.25 => 2.2.25 gatsby-transformer-remark: ^2.6.22 => 2.6.22 gatsby-transformer-sharp: ^2.2.14 => 2.2.14 npmGlobalPackages: gatsby-cli: 2.8.29

[AAverin]

Maybe docs need to be updated? I am using MDXRenderer and nothing was accessible until I have manually passed a parameter

<MDXRenderer frontmatter={mdx.frontmatter}>{mdx.body}</MDXRenderer>

[lambertbrady]

I’ve run into the same problem - on top of that, passing frontmatter as a prop to MDXRenderer breaks the build when trying to use it, even though gatsby develop works just fine. Here’s my usage:

In my post component: <MDXRenderer frontmatter={post.frontmatter}>{post.body}</MDXRenderer>

In my index.mdx file:

---
title: Hello World
---

<p>{props.frontmatter.title}</p>

Running gatsby develop displays the frontmatter output as expected. Running gatsby build throws an error:

gatsby-plugin-mdx
TypeError: Cannot read property 'title' of undefined