Thanks this is great. I think this tricked me up in some existing code, when an Object is used as an object, and separately as key/values

const {
  pageContext,
  data: {
    allMarkdownRemark: { edges }
  }
} = this.props;
const { data: { allMarkdownRemark } } = this.props;
...
// from: this.props.data.allMarkdownRemark.edges
// to : edges
// from: this.props.data.allMarkdownRemark;
// to: allMarkdownRemark

Heck, I could clean it up a little more:

const { data: { allMarkdownRemark } } = this.props;
const { 
  pageContext,
  allMarkdownRemark: { edges }
} = this.props;