fix(config): load env and file source order bug (#1220)

* fix config load env & file order bug

* fix watch issue

* return empty as each update can be resolved

config/config.go

@@ -67,11 +67,15 @@ func (c *config) watch(w Watcher) {
 		kvs, err := w.Next()
 		if err != nil {
 			time.Sleep(time.Second)
-			c.log.Errorf("Failed to watch next config: %v", err)
+			c.log.Errorf("failed to watch next config: %v", err)
 			continue
 		}
 		if err := c.reader.Merge(kvs...); err != nil {
-			c.log.Errorf("Failed to merge next config: %v", err)
+			c.log.Errorf("failed to merge next config: %v", err)
+			continue
+		}
+		if err := c.reader.Resolve(); err != nil {
+			c.log.Errorf("failed to resolve next config: %v", err)
 			continue
 		}
 		c.cached.Range(func(key, value interface{}) bool {
@@ -95,16 +99,20 @@ func (c *config) Load() error {
 			return err
 		}
 		if err := c.reader.Merge(kvs...); err != nil {
-			c.log.Errorf("Failed to merge config source: %v", err)
+			c.log.Errorf("failed to merge config source: %v", err)
 			return err
 		}
 		w, err := src.Watch()
 		if err != nil {
-			c.log.Errorf("Failed to watch config source: %v", err)
+			c.log.Errorf("failed to watch config source: %v", err)
 			return err
 		}
 		go c.watch(w)
 	}
+	if err := c.reader.Resolve(); err != nil {
+		c.log.Errorf("failed to resolve config source: %v", err)
+		return err
+	}
 	return nil
 }
 

config/env/env_test.go

@@ -58,8 +58,8 @@ func TestEnvWithPrefix(t *testing.T) {
 	}
 
 	c := config.New(config.WithSource(
-		NewSource(prefix1, prefix2),
 		file.NewSource(path),
+		NewSource(prefix1, prefix2),
 	))
 
 	if err := c.Load(); err != nil {

config/reader.go

@@ -17,6 +17,7 @@ type Reader interface {
 	Merge(...*KeyValue) error
 	Value(string) (Value, bool)
 	Source() ([]byte, error)
+	Resolve() error
 }
 
 type reader struct {
@@ -45,9 +46,6 @@ func (r *reader) Merge(kvs ...*KeyValue) error {
 			return err
 		}
 	}
-	if err := r.opts.resolver(merged); err != nil {
-		return err
-	}
 	r.values = merged
 	return nil
 }
@@ -60,6 +58,10 @@ func (r *reader) Source() ([]byte, error) {
 	return marshalJSON(convertMap(r.values))
 }
 
+func (r *reader) Resolve() error {
+	return r.opts.resolver(r.values)
+}
+
 func cloneMap(src map[string]interface{}) (map[string]interface{}, error) {
 	// https://gist.github.com/soroushjp/0ec92102641ddfc3ad5515ca76405f4d
 	var buf bytes.Buffer