Closes spf13/afero#79

Added fix to support "nested" `BasePathFs`. Unit-tests are also included.

basepath.go

@@ -29,7 +29,6 @@ func NewBasePathFs(source Fs, path string) Fs {
 // on a file outside the base path it returns the given file name and an error,
 // else the given file with the base path prepended
 func (b *BasePathFs) RealPath(name string) (path string, err error) {
-
 	if err := validateBasePathName(name); err != nil {
 		return "", err
 	}
@@ -39,6 +38,11 @@ func (b *BasePathFs) RealPath(name string) (path string, err error) {
 	if !strings.HasPrefix(path, bpath) {
 		return name, os.ErrNotExist
 	}
+
+	if parentBasePathFs, ok := b.source.(*BasePathFs); ok {
+		return parentBasePathFs.RealPath(path)
+	}
+
 	return path, nil
 }
 

basepath_test.go

@@ -90,3 +90,40 @@ func TestRealPath(t *testing.T) {
 	}
 
 }
+
+func TestNestedBasePaths(t *testing.T) {
+	type dirSpec struct {
+		Dir1, Dir2, Dir3 string
+	}
+	dirSpecs := []dirSpec{
+		dirSpec{Dir1: "/", Dir2: "/", Dir3: "/"},
+		dirSpec{Dir1: "/", Dir2: "/path2", Dir3: "/"},
+		dirSpec{Dir1: "/path1/dir", Dir2: "/path2/dir/", Dir3: "/path3/dir"},
+	}
+
+	for _, ds := range dirSpecs {
+		memFs := NewMemMapFs()
+		level1Fs := NewBasePathFs(memFs, ds.Dir1)
+		level2Fs := NewBasePathFs(level1Fs, ds.Dir2)
+		level3Fs := NewBasePathFs(level2Fs, ds.Dir3)
+
+		type spec struct {
+			BaseFs       Fs
+			FileName     string
+			ExpectedPath string
+		}
+		specs := []spec{
+			spec{BaseFs: level3Fs, FileName: "f.txt", ExpectedPath: filepath.Join(ds.Dir1, ds.Dir2, ds.Dir3, "f.txt")},
+			spec{BaseFs: level2Fs, FileName: "f.txt", ExpectedPath: filepath.Join(ds.Dir1, ds.Dir2, "f.txt")},
+			spec{BaseFs: level1Fs, FileName: "f.txt", ExpectedPath: filepath.Join(ds.Dir1, "f.txt")},
+		}
+
+		for _, s := range specs {
+			if actualPath, err := s.BaseFs.(*BasePathFs).RealPath(s.FileName); err != nil {
+				t.Errorf("Got error %s", err.Error())
+			} else if actualPath != s.ExpectedPath {
+				t.Errorf("Expected \n%s got \n%s", s.ExpectedPath, actualPath)
+			}
+		}
+	}
+}