plumbing/object: do not eat error on tree decode

plumbing/object/tree.go

@@ -136,9 +136,9 @@ func (t *Tree) dir(baseName string) (*Tree, error) {
 	}
 
 	tree := &Tree{s: t.s}
-	tree.Decode(obj)
+	err = tree.Decode(obj)
 
-	return tree, nil
+	return tree, err
 }
 
 var errEntryNotFound = errors.New("entry not found")

plumbing/object/tree_test.go

@@ -1,6 +1,7 @@
 package object
 
 import (
+	"errors"
 	"io"
 
 	"gopkg.in/src-d/go-git.v4/plumbing"
@@ -113,6 +114,42 @@ func (s *TreeSuite) TestFindEntry(c *C) {
 	c.Assert(e.Name, Equals, "foo.go")
 }
 
+// Overrides returned plumbing.EncodedObject for given hash.
+// Otherwise, delegates to actual storer to get real object
+type fakeStorer struct {
+	storer.EncodedObjectStorer
+	hash plumbing.Hash
+	fake fakeEncodedObject
+}
+
+func (fs fakeStorer) EncodedObject(t plumbing.ObjectType, h plumbing.Hash) (plumbing.EncodedObject, error) {
+	if fs.hash == h {
+		return fs.fake, nil
+	}
+	return fs.EncodedObjectStorer.EncodedObject(t, h)
+}
+
+// Overrides reader of plumbing.EncodedObject to simulate read error
+type fakeEncodedObject struct{ plumbing.EncodedObject }
+
+func (fe fakeEncodedObject) Reader() (io.ReadCloser, error) {
+	return nil, errors.New("Simulate encoded object can't be read")
+}
+
+func (s *TreeSuite) TestDir(c *C) {
+	vendor, err := s.Tree.dir("vendor")
+	c.Assert(err, IsNil)
+
+	t, err := GetTree(s.Tree.s, s.Tree.ID())
+	c.Assert(err, IsNil)
+	o, err := t.s.EncodedObject(plumbing.AnyObject, vendor.ID())
+	c.Assert(err, IsNil)
+
+	t.s = fakeStorer{t.s, vendor.ID(), fakeEncodedObject{o}}
+	_, err = t.dir("vendor")
+	c.Assert(err, NotNil)
+}
+
 // This plumbing.EncodedObject implementation has a reader that only returns 6
 // bytes at a time, this should simulate the conditions when a read
 // returns less bytes than asked, for example when reading a hash which