Add support for "orb.yml" case to merge contents under the parent

This case occurs only under the following situations:

* we're on a leaf node that is a file AND
* it's siblings are all _only_ directories

We'll probably need to tweak this a little in the case we want to
support merging other files at this level of the tree.

`usage.yml` maybe one such case.

This change also identified a case where this type of file,
let's call it the "root file" can appear at the top-level of a tree.

In this case the contents of the root file are nested under a key by
the same name of the path which we started.

At the moment, this means in our tests we'd add a key named after the
temporary file path we constructed for our test environment. :/

filetree/filetree.go

@@ -1,12 +1,12 @@
 package filetree
 
 import (
-	"encoding/json"
 	"fmt"
 	"io/ioutil"
 	"os"
 	"path/filepath"
 
+	"github.com/mitchellh/mapstructure"
 	yaml "gopkg.in/yaml.v2"
 )
 
@@ -34,11 +34,12 @@ func (n Node) marshalParent() (interface{}, error) {
 			return tree, err
 		}
 
-		if len(child.siblings()) > 0 {
-			result := make(map[string]interface{})
-			merge, _ := json.Marshal(c)
-			json.Unmarshal(merge, &result)
-			tree[child.Parent.Info.Name()] = result
+		if len(child.siblings()) > 0 && child.onlyFile() {
+			find := make(map[string]interface{})
+			if err := mapstructure.Decode(c, &find); err != nil {
+				panic(err)
+			}
+			tree[child.Parent.Info.Name()] = find
 		} else {
 			tree[child.Info.Name()] = c
 		}
@@ -47,6 +48,19 @@ func (n Node) marshalParent() (interface{}, error) {
 	return tree, nil
 }
 
+// Returns true/false if this node is the only file of it's siblings
+func (n Node) onlyFile() bool {
+	if n.Info.IsDir() {
+		return false
+	}
+	for _, v := range n.siblings() {
+		if v.Info.IsDir() {
+			return true
+		}
+	}
+	return false
+}
+
 func (n Node) siblings() []*Node {
 	siblings := []*Node{}
 	for _, child := range n.Parent.Children {

filetree/filetree_test.go

@@ -30,15 +30,13 @@ var _ = Describe("filetree", func() {
 	})
 
 	Describe("NewTree", func() {
-		var rootFile, subDir, subDirFile, emptyDir string
+		var subDir, subDirFile, emptyDir string
 
 		BeforeEach(func() {
-			rootFile = filepath.Join(tempRoot, "root_file.yml")
 			subDir = filepath.Join(tempRoot, "sub_dir")
 			subDirFile = filepath.Join(tempRoot, "sub_dir", "sub_dir_file.yml")
 			emptyDir = filepath.Join(tempRoot, "empty_dir")
 
-			Expect(ioutil.WriteFile(rootFile, []byte("foo:\n  bar"), 0600)).To(Succeed())
 			Expect(os.Mkdir(subDir, 0700)).To(Succeed())
 			Expect(ioutil.WriteFile(subDirFile, []byte("foo:\n  bar:\n    baz"), 0600)).To(Succeed())
 			Expect(os.Mkdir(emptyDir, 0700)).To(Succeed())
@@ -64,22 +62,20 @@ var _ = Describe("filetree", func() {
 			Expect(tree.FullPath).To(Equal(tempRoot))
 			Expect(tree.Info.Name()).To(Equal(filepath.Base(tempRoot)))
 
-			Expect(tree.Children).To(HaveLen(3))
+			Expect(tree.Children).To(HaveLen(2))
 			sort.Slice(tree.Children, func(i, j int) bool {
 				return tree.Children[i].FullPath < tree.Children[j].FullPath
 			})
 
 			Expect(tree.Children[0].Info.Name()).To(Equal("empty_dir"))
 			Expect(tree.Children[0].FullPath).To(Equal(emptyDir))
 
-			Expect(tree.Children[1].Info.Name()).To(Equal("root_file.yml"))
-			Expect(tree.Children[1].FullPath).To(Equal(rootFile))
-			Expect(tree.Children[2].Info.Name()).To(Equal("sub_dir"))
-			Expect(tree.Children[2].FullPath).To(Equal(subDir))
+			Expect(tree.Children[1].Info.Name()).To(Equal("sub_dir"))
+			Expect(tree.Children[1].FullPath).To(Equal(subDir))
 
-			Expect(tree.Children[2].Children).To(HaveLen(1))
-			Expect(tree.Children[2].Children[0].Info.Name()).To(Equal("sub_dir_file.yml"))
-			Expect(tree.Children[2].Children[0].FullPath).To(Equal(subDirFile))
+			Expect(tree.Children[1].Children).To(HaveLen(1))
+			Expect(tree.Children[1].Children[0].Info.Name()).To(Equal("sub_dir_file.yml"))
+			Expect(tree.Children[1].Children[0].FullPath).To(Equal(subDirFile))
 		})
 
 		It("renders to YAML", func() {
@@ -88,10 +84,7 @@ var _ = Describe("filetree", func() {
 
 			out, err := yaml.Marshal(tree)
 			Expect(err).ToNot(HaveOccurred())
-			Expect(out).To(MatchYAML(`root_file.yml:
-  foo:
-    bar
-empty_dir: null
+			Expect(out).To(MatchYAML(`empty_dir: null
 sub_dir:
   sub_dir_file.yml:
     foo: