Gatsby: [www] gatsby develop error

[m-allanson]

Description

Editing a markdown file can cause the site to error while gatsby develop is running.

Environment

Gatsby version: from master
Node.js version: 9.5.0
Operating System: macOS

File contents (if changed):

see https://github.com/gatsbyjs/gatsby/tree/c246262d10830eda09135ff5f8a3ee64883757ce/www

Actual result

Page displays an error:

Expected behavior

Page should not display an error 😄

Steps to reproduce

• in this repo, cd www
• rm -r .cache
• yarn run develop
• browse to http://localhost:8000/docs/graphql-reference/
• edit and save docs/docs/graphql-reference.md
• wait for auto-page reload (or refresh the browser)
• There will be an error TypeError: Cannot read property 'markdownRemark' of undefined, which will remain until deleting the .cache directory

I've been able to recreate this with various docs pages and blog posts - all markdown files. Maybe the query data isn't being retrieved from the cache properly?

This query will still work in graphiql:

{    
  markdownRemark(fields: { slug: { eq: "/docs/querying-with-graphql/" } }) {
      html
      excerpt
      timeToRead
      fields {
        slug
        anchor
      }
      frontmatter {
        title
      }

    }
}

[fk]

Saw this too just now.

[m-allanson]

I wonder if this is similar to the issue that @peduarte was seeing earlier today?

[peduarte]

Nope, actually my issue was me being stupid and using mutable array methods on props.data 😒🔫

[davidvenin]

I got the same issue. If I had link in .md, browser throw me the exact same error.
[Edit] I don't know why but It seems a little bit random to me. I didn't change anything and it works now. \o/
[Edit 2] I add a new link and got the error again.

[gurtjun]

Same issue here, every time I edit a markdown file.

[peduarte]

but yeah this issue happens to me, when I edit a markdown file. but not ALL the time.

[patrickodacre]

I'm seeing this issue, too. Bare bones Gatsby install. Just added transformer remark. Most edits to my .md file break the develop build and I have to restart the server to get it working again.

[KyleAMathews]

This should have fixed the bug, thanks for your patience!

https://github.com/gatsbyjs/gatsby/pull/4213/files/cb52bc81b85f466e846da528bc0ec9b0eead9ec4#diff-a45448af33cc109010d5aab8911336dd