printTypeDefinitions throws TypeError: flatMap is not a function

[m4rrc0]

Edit: I found the bug. See second comment.

Description

I am trying to use gatsby-plugin-schema-snapshot and it throws TypeError: flatMap is not a function.
This throws as well:

exports.createSchemaCustomization = ({ actions }) => {
  actions.printTypeDefinitions({});
};

Steps to reproduce

1. Create a new project.
2. Add gatsby-plugin-schema-snapshot to the project or the above mentioned snippet in gatsby-node.js
3. gatsby develop or gatsby build

Demo repo
Full log on Netlify

I was initially on NodeJS 10 (like Netlify is on the build above). I tried upgrading to Node 13 in case the polyfill was causing the problem but no luck.

Expected result

Should produce a schema.gql file

Actual result

TypeError: flatMap is not a function
See full log on Netlify

Environment

  System:
    OS: Linux 4.19 Debian GNU/Linux 9 (stretch) 9 (stretch)
    CPU: (8) x64 06/8e
    Shell: 5.3.1 - /usr/bin/zsh
  Binaries:
    Node: 13.0.1 - /usr/bin/node
    Yarn: 1.19.1 - /usr/bin/yarn
    npm: 6.12.0 - /usr/bin/npm
  Languages:
    Python: 2.7.13 - /usr/bin/python
  Browsers:
    Firefox: 60.9.0
  npmPackages:
    gatsby: ^2.17.6 => 2.17.6
    gatsby-image: ^2.2.30 => 2.2.30
    gatsby-plugin-manifest: ^2.2.25 => 2.2.25
    gatsby-plugin-offline: ^3.0.17 => 3.0.17
    gatsby-plugin-react-helmet: ^3.1.13 => 3.1.13
    gatsby-plugin-schema-snapshot: ^1.0.0 => 1.0.0
    gatsby-plugin-sharp: ^2.2.34 => 2.2.34
    gatsby-source-filesystem: ^2.1.35 => 2.1.35
    gatsby-transformer-sharp: ^2.3.1 => 2.3.1

[m4rrc0]

What is strange is that I tried the snippet I mention a couple months back and all was working fine. I tried downgrading the gatsby package to the version I used back then but it didn't work either. Maybe a dependency changed...?

[m4rrc0]

Oh I've found the bug:
flatMap is indeed a function
It is a default export.
In gatsby, it is not imported as default

FIX:

- const { flatMap } = require(`graphql/polyfills/flatMap`)

+ const flatMap = require(`graphql/polyfills/flatMap`).default

I don't have time for a PR right now, sorry... =/

[m4rrc0]

Such a simple PR... (#19208) I tried creating it from Github UI directly.
Please tell me if it is ok. I know I am supposed to fork and so on but this makes the process so much easier.

[stefanprobst]

should be fixed by #19208