new reader auto fallback to env

.travis.yml

@@ -8,7 +8,7 @@ before_install:
   - go get github.com/mattn/goveralls
 
 env:
-  - GO111MODULE=on DATA1=true DATA2=false DATA3=9 DATA4=0 DATA5=3m5s EMPTY="" DATA6="aGVsbG8="
+  - GO111MODULE=on DATA1=true DATA2=false DATA3=9 DATA4=0 DATA5=3m5s EMPTY="" DATA6="aGVsbG8=" ONLYENV=1
 
 script:
   - $HOME/gopath/bin/goveralls -service=travis-ci

Makefile

@@ -7,4 +7,5 @@ test:
 		DATA5=3m5s \
 		DATA6="aGVsbG8=" \
 		EMPTY="" \
+		ONLYENV=1 \
 		go test ./...

configfile.go

@@ -16,9 +16,9 @@ func NewReader(base string) *Reader {
 	stats, _ := os.Stat(base)
 	if stats != nil {
 		if stats.IsDir() {
-			return NewDirReader(base)
+			return NewDirReader(base).Fallback(NewEnvReader())
 		}
-		return NewYAMLReader(base)
+		return NewYAMLReader(base).Fallback(NewEnvReader())
 	}
 	return NewEnvReader()
 }

configfile_test.go

@@ -479,4 +479,6 @@ func TestFallback(t *testing.T) {
 	t.Parallel()
 
 	testReader(t, configfile.NewDirReader("notexists").Fallback(configfile.NewEnvReader()))
+
+	assert.Equal(t, 1, configfile.NewReader("testdata/config.yaml").Int("ONLYENV"))
 }