remove optional moduleExportName and align on default

Author: Laurie Barth

packages/gatsby-plugin-theme-ui/gatsby-node.js

@@ -29,21 +29,19 @@ exports.createSchemaCustomization = ({ actions }) => {
       type ThemeUiConfig implements Node {
         themeModule: JSON,
         themeModulePath: JSON,
-        moduleExportName: String,
       }
     `)
   }
 
   exports.sourceNodes = (
     { actions, createContentDigest },
-    { moduleExportName = 'default', themeModule, themeModulePath}
+    { themeModule, themeModulePath}
   ) => {      
     const { createNode } = actions
 
     const themeUiConfig = {
         themeModule,
         themeModulePath,
-        moduleExportName,
     }
 
     createNode({

packages/gatsby-plugin-theme-ui/src/hooks/configOptions.js

@@ -6,7 +6,6 @@ const useThemeUiConfig = () => {
       themeUiConfig(id: { eq: "gatsby-plugin-theme-ui-config" }) {
         themeModule
         themeModulePath
-        moduleExportName
       }
     }
   `)

packages/gatsby-plugin-theme-ui/src/provider.js

@@ -11,7 +11,7 @@ import useThemeUiConfig from './hooks/configOptions'
 
 const Root = ({children}) => {
   const themeUiConfig = useThemeUiConfig()
-  const {themeModule, themeModulePath, moduleExportName} = themeUiConfig
+  const {themeModule, themeModulePath} = themeUiConfig
 
   let themeWrapper
   if (themeModule) {
@@ -22,8 +22,8 @@ const Root = ({children}) => {
     themeWrapper = themeModulePath
   }
 
-  if(themeWrapper && (moduleExportName in themeWrapper)) {
-    themeWrapper = themeWrapper[moduleExportName]
+  if(themeWrapper && ('default' in themeWrapper)) {
+    themeWrapper = themeWrapper.default
   }
 
   themeWrapper = merge(themeWrapper, {