Alerting: Marshal incoming json.RawMessage in diff (#84692)

This will ensure the encoding is correct when comparing
to the existing rule.

pkg/services/ngalert/models/alert_rule.go

@@ -346,7 +346,11 @@ func (alertRule *AlertRule) Diff(rule *AlertRule, ignore ...string) cmputil.Diff
 
 	// json.RawMessage is a slice of bytes and therefore cmp's default behavior is to compare it by byte, which is not really useful
 	var jsonCmp = cmp.Transformer("", func(in json.RawMessage) string {
-		return string(in)
+		b, err := json.Marshal(in)
+		if err != nil {
+			return string(in)
+		}
+		return string(b)
 	})
 	ops = append(
 		ops,

pkg/services/ngalert/models/alert_rule_test.go

@@ -656,6 +656,21 @@ func TestDiff(t *testing.T) {
 			}
 		})
 
+		t.Run("should correctly detect no change with '<' and '>' in query", func(t *testing.T) {
+			old := query1
+			new := query1
+			old.Model = json.RawMessage(`{"field1": "$A \u003c 1"}`)
+			new.Model = json.RawMessage(`{"field1": "$A < 1"}`)
+			rule1.Data = []AlertQuery{old}
+			rule2.Data = []AlertQuery{new}
+
+			diff := rule1.Diff(rule2)
+			assert.Nil(t, diff)
+
+			// reset rule1
+			rule1.Data = []AlertQuery{query1}
+		})
+
 		t.Run("should detect new changes in array if too many fields changed", func(t *testing.T) {
 			query2 := query1
 			query2.QueryType = "test"