Handle empty maps properly using old logic (not explicitly set) and n…

…ew logic (declared as {})

pkg/validation/limits.go

@@ -478,6 +478,18 @@ func (l *Limits) UnmarshalYAML(unmarshal func(interface{}) error) error {
 			return errors.Wrap(err, "cloning limits (unmarshaling)")
 		}
 	}
+
+	// Check if we're getting an empty map for RulerRemoteWriteHeaders
+	var raw map[string]interface{}
+	if err := unmarshal(&raw); err != nil {
+		return err
+	}
+
+	if v, ok := raw["ruler_remote_write_headers"]; ok && v == nil {
+		l.RulerRemoteWriteHeaders = OverwriteMarshalingStringMap{m: nil}
+	}
+
+	// Now unmarshal the full config
 	if err := unmarshal((*plain)(l)); err != nil {
 		return err
 	}
@@ -1205,14 +1217,38 @@ func (sm OverwriteMarshalingStringMap) MarshalYAML() (interface{}, error) {
 	return sm.m, nil
 }
 
+// UnmarshalYAML implements yaml.Unmarshaler.
 func (sm *OverwriteMarshalingStringMap) UnmarshalYAML(unmarshal func(interface{}) error) error {
-	var def map[string]string
+	var raw interface{}
+	if err := unmarshal(&raw); err != nil {
+		return err
+	}
 
-	err := unmarshal(&def)
-	if err != nil {
+	// If we get a nil value or empty map, set a nil map
+	if raw == nil {
+		sm.m = nil
+		return nil
+	}
+
+	// Check for empty map in different YAML representations
+	switch v := raw.(type) {
+	case map[interface{}]interface{}:
+		if len(v) == 0 {
+			sm.m = nil
+			return nil
+		}
+	case map[string]interface{}:
+		if len(v) == 0 {
+			sm.m = nil
+			return nil
+		}
+	}
+
+	// Otherwise try to unmarshal as a map
+	var def map[string]string
+	if err := unmarshal(&def); err != nil {
 		return err
 	}
 	sm.m = def
-
 	return nil
 }

pkg/validation/limits_test.go

@@ -233,6 +233,24 @@ ruler_remote_write_headers:
 			desc: "empty map overrides defaults",
 			yaml: `
 ruler_remote_write_headers:
+`,
+			exp: Limits{
+				DiscoverServiceName: []string{},
+				LogLevelFields:      []string{},
+				// Rest from new defaults
+				StreamRetention: []StreamRetention{
+					{
+						Period:   model.Duration(24 * time.Hour),
+						Selector: `{a="b"}`,
+					},
+				},
+				OTLPConfig: defaultOTLPConfig,
+			},
+		},
+		{
+			desc: "explicitly set empty map overrides defaults",
+			yaml: `
+ruler_remote_write_headers: {} # Explicitly set an empty map
 `,
 			exp: Limits{
 				DiscoverServiceName: []string{},
@@ -318,7 +336,7 @@ query_timeout: 5m
 			var out Limits
 			decoder := yaml.NewDecoder(bytes.NewReader([]byte(tc.yaml)))
 			decoder.KnownFields(true)
-			err := decoder.Decode(out)
+			err := decoder.Decode(&out)
 			require.NoError(t, err)
 			require.Equal(t, tc.exp, out)
 		})