fix: adding a dir: leaf node gets replaced with dir if necessary

src/importer/dir-flat.js

@@ -7,9 +7,11 @@ const dagPB = require('ipld-dag-pb')
 const UnixFS = require('ipfs-unixfs')
 const DAGLink = dagPB.DAGLink
 const DAGNode = dagPB.DAGNode
+const Dir = require('./dir')
 
-class DirFlat {
+class DirFlat extends Dir {
   constructor (props) {
+    super()
     this._children = {}
     Object.assign(this, props)
   }

src/importer/dir-sharded.js

@@ -9,6 +9,7 @@ const UnixFS = require('ipfs-unixfs')
 const DAGLink = dagPB.DAGLink
 const DAGNode = dagPB.DAGNode
 const multihashing = require('multihashing-async')
+const Dir = require('./dir')
 
 const Bucket = require('../hamt')
 
@@ -38,8 +39,9 @@ const defaultOptions = {
   hashFn: hashFn
 }
 
-class DirSharded {
+class DirSharded extends Dir {
   constructor (props, _options) {
+    super()
     const options = Object.assign({}, defaultOptions, _options)
     this._options = options
     this._bucket = Bucket(options)

src/importer/dir.js

@@ -0,0 +1,4 @@
+'use strict'
+
+module.exports = class Dir {
+}

src/importer/tree-builder.js

@@ -8,6 +8,7 @@ const writable = require('pull-write')
 const pushable = require('pull-pushable')
 const DirFlat = require('./dir-flat')
 const flatToShard = require('./flat-to-shard')
+const Dir = require('./dir')
 
 module.exports = createTreeBuilder
 
@@ -122,7 +123,7 @@ function createTreeBuilder (ipldResolver, _options) {
             return // early
           }
           let dir = treeNode
-          if (!dir) {
+          if (!dir || !(dir instanceof Dir)) {
             dir = DirFlat({
               dir: true,
               parent: parent,