added allowEmptyMap option

viper.go

@@ -205,6 +205,7 @@ type Viper struct {
 	automaticEnvApplied bool
 	envKeyReplacer      StringReplacer
 	allowEmptyEnv       bool
+	allowEmptyMap       bool
 
 	config         map[string]interface{}
 	override       map[string]interface{}
@@ -526,6 +527,15 @@ func (v *Viper) mergeWithEnvPrefix(in string) string {
 	return strings.ToUpper(in)
 }
 
+// AllowEmptyMap tells Viper to consider set,
+// but empty maps as valid values instead of falling back.
+// For backward compatibility reasons this is false by default.
+func AllowEmptyMap(allowEmptyMap bool) { v.AllowEmptyMap(allowEmptyMap) }
+
+func (v *Viper) AllowEmptyMap(allowEmptyMap bool) {
+	v.allowEmptyMap = allowEmptyMap
+}
+
 // AllowEmptyEnv tells Viper to consider set,
 // but empty environment variables as valid values instead of falling back.
 // For backward compatibility reasons this is false by default.
@@ -2011,6 +2021,14 @@ func (v *Viper) flattenAndMergeMap(shadow map[string]bool, m map[string]interfac
 			shadow[strings.ToLower(fullKey)] = true
 			continue
 		}
+
+		if v.allowEmptyMap {
+			if len(val.(map[string]interface{})) == 0 {
+				shadow[strings.ToLower(fullKey)] = true
+				continue
+			}
+		}
+
 		// recursively merge to shadow map
 		shadow = v.flattenAndMergeMap(shadow, m2, fullKey)
 	}

viper_test.go

@@ -60,6 +60,8 @@ type testUnmarshalExtra struct {
 var tomlExample = []byte(`
 title = "TOML Example"
 
+[empty.map]
+
 [owner]
 organization = "MongoDB"
 Bio = "MongoDB Chief Developer Advocate & Hacker at Large"
@@ -669,6 +671,16 @@ func TestEmptyEnv_Allowed(t *testing.T) {
 	assert.Equal(t, "Cake", Get("name"))
 }
 
+func TestEmptyMap_Allowed(t *testing.T) {
+	initTOML()
+	AllowEmptyMap(true)
+
+	allkeys := sort.StringSlice(AllKeys())
+	allkeys.Sort()
+
+	assert.Equal(t, sort.StringSlice(sort.StringSlice{"empty.map", "owner.bio", "owner.dob", "owner.organization", "title"}), allkeys)
+}
+
 func TestEnvPrefix(t *testing.T) {
 	initJSON()