src/handle-glamorous-references.js
function getDisplayName(path) {
    const componentName = getName(path)
    const filename = getFileName(file)
    if (filename) {
      if (filename === componentName) {
        return componentName
      }
      return componentName ? `${filename}__${componentName}` : filename
    } else {
      return componentName
    }
  }
function getDisplayName(path) {
    const componentName = getName(path)
    const filename = getFileName(file)
    if (filename) {
      if (filename === componentName) {
        return componentName
      }
      return componentName ? `${filename}__${componentName}` : filename
    } else {
      return componentName
    }
  }
credit: https://github.com/styled-components/babel-plugin-styled-components/blob/37a13e9c21c52148ce6e403100df54c0b1561a88/src/visitors/displayNameAndId.js