gatsby: [gatsby-transformer-react-docgen] throws conflicting field types warning

Description

gatsby-transformer-react-docgen throws “There are conflicting field types in your data” warning depending on the PropTypes.

Here are two components that conflict:

Button.propTypes = {
  type: PropTypes.oneOf(['button', 'submit']),
}

DatePicker.propTypes = {
  lastMonth: PropTypes.instanceOf(Date),
}

Steps to reproduce

I’ve created a repo to demonstrate this bug:

1. git clone git@github.com:danoc/gatsby-react-docgen-repro.git && cd gatsby-react-docgen-repro && yarn && yarn develop
2. See warning in console.

Expected result

Shouldn’t start development environment without throwing warning.

Actual result

Warning appears:

warning There are conflicting field types in your data. GraphQL schema will omit those fields.
ComponentProp.type.value:
 - type: array<object>
   value: [ { value: '\'button\'', computed: false }, ... ]
   source: File "conflicting-components/Button.jsx"
 - type: string
   value: 'Date'
   source: File "conflicting-components/DatePicker.jsx"
ComponentProp.parentType.value:
 - type: array<object>
   value: [ { value: '\'button\'', computed: false }, ... ]
   source: File "conflicting-components/Button.jsx"
 - type: string
   value: 'Date'
   source: File "conflicting-components/DatePicker.jsx"

Environment

I’m running v2, but this happens in both v1 and v2.

  System:
    OS: macOS High Sierra 10.13.6
    CPU: x64 Intel(R) Core(TM) i7-4980HQ CPU @ 2.80GHz
    Shell: 5.5.1 - /usr/local/bin/zsh
  Binaries:
    Node: 8.11.3 - ~/.nvm/versions/node/v8.11.3/bin/node
    Yarn: 1.7.0 - /usr/local/bin/yarn
    npm: 5.6.0 - ~/.nvm/versions/node/v8.11.3/bin/npm
  Browsers:
    Chrome: 68.0.3440.84
    Firefox: 61.0.1
    Safari: 11.1.2
  npmPackages:
    gatsby: next => 2.0.0-beta.69
    gatsby-source-filesystem: next => 2.0.1-beta.10
    gatsby-transformer-react-docgen: next => 2.1.1-beta.4

File contents (if changed)

gatsby-config.js: N/A package.json: N/A gatsby-node.js: N/A gatsby-browser.js: N/A gatsby-ssr.js: N/A