types: compile type assertions to avoid sneaky runtime surprises

Ensure that the types in result.go implement both
json.Marshaler and json.Unmarshaler
and thus avoid any accidental deletions of their respective
methods which would then cause surprises at runtime.

types/result.go

@@ -2,6 +2,7 @@ package types
 
 import (
 	"bytes"
+	"encoding/json"
 	"fmt"
 
 	"github.com/gogo/protobuf/jsonpb"
@@ -137,3 +138,18 @@ func (r *ResponseCommit) UnmarshalJSON(b []byte) error {
 	reader := bytes.NewBuffer(b)
 	return jsonpbUnmarshaller.Unmarshal(reader, r)
 }
+
+// Some compile time assertions to ensure we don't
+// have accidental runtime surprises later on.
+
+// jsonEncodingRoundTripper ensures that asserted
+// interfaces implement both MarshalJSON and UnmarshalJSON
+type jsonRoundTripper interface {
+	json.Marshaler
+	json.Unmarshaler
+}
+
+var _ jsonRoundTripper = (*ResponseCommit)(nil)
+var _ jsonRoundTripper = (*ResponseQuery)(nil)
+var _ jsonRoundTripper = (*ResponseDeliverTx)(nil)
+var _ jsonRoundTripper = (*ResponseSetOption)(nil)