Fix tracking parent nodes when loading redux state from cache (#4013)

fixes #2929

packages/gatsby/src/redux/index.js

@@ -12,15 +12,34 @@ const emitter = mitt()
 // Reducers
 const reducers = require(`./reducers`)
 
+// Parent node tracking
+const rootNodeMap = new WeakMap()
+const addParentToSubObjects = (data, parentId) => {
+  if (_.isPlainObject(data) || _.isArray(data)) {
+    _.each(data, o => addParentToSubObjects(o, parentId))
+    rootNodeMap.set(data, parentId)
+  }
+}
+
+const trackSubObjectsToRootNodeId = node => {
+  _.each(node, (v, k) => {
+    // Ignore the node internal object.
+    if (k === `internal`) {
+      return
+    }
+    addParentToSubObjects(v, node.parent)
+  })
+}
+exports.trackSubObjectsToRootNodeId = trackSubObjectsToRootNodeId
+
 // Read from cache the old node data.
 let initialState = {}
-const rootNodeMap = new WeakMap()
 try {
   initialState = JSON.parse(
     fs.readFileSync(`${process.cwd()}/.cache/redux-state.json`)
   )
 
-  _.each(initialState.nodes, (id, node) => {
+  _.each(initialState.nodes, node => {
     trackSubObjectsToRootNodeId(node)
   })
 } catch (e) {
@@ -121,24 +140,6 @@ exports.getNodeAndSavePathDependency = (id, path) => {
 
 exports.getRootNodeId = node => rootNodeMap.get(node)
 
-const addParentToSubObjects = (data, parentId) => {
-  if (_.isPlainObject(data) || _.isArray(data)) {
-    _.each(data, o => addParentToSubObjects(o, parentId))
-    rootNodeMap.set(data, parentId)
-  }
-}
-
-const trackSubObjectsToRootNodeId = node => {
-  _.each(node, (v, k) => {
-    // Ignore the node internal object.
-    if (k === `internal`) {
-      return
-    }
-    addParentToSubObjects(v, node.parent)
-  })
-}
-exports.trackSubObjectsToRootNodeId = trackSubObjectsToRootNodeId
-
 // Start plugin runner which listens to the store
 // and invokes Gatsby API based on actions.
 require(`./plugin-runner`)