Fix JSON encoding for pointer to structs implementing json.Marshaler

https://github.com/jackc/pgx/issues/1681

pgtype/json.go

@@ -25,6 +25,13 @@ func (c JSONCodec) PlanEncode(m *Map, oid uint32, format int16, value any) Encod
 	case []byte:
 		return encodePlanJSONCodecEitherFormatByteSlice{}
 
+	// Must come before trying wrap encode plans because a pointer to a struct may be unwrapped to a struct that can be
+	// marshalled.
+	//
+	// https://github.com/jackc/pgx/issues/1681
+	case json.Marshaler:
+		return encodePlanJSONCodecEitherFormatMarshal{}
+
 	// Cannot rely on driver.Valuer being handled later because anything can be marshalled.
 	//
 	// https://github.com/jackc/pgx/issues/1430

pgtype/json_test.go

@@ -133,3 +133,27 @@ func TestJSONCodecClearExistingValueBeforeUnmarshal(t *testing.T) {
 		require.Equal(t, map[string]any{"baz": "quz"}, m)
 	})
 }
+
+type ParentIssue1681 struct {
+	Child ChildIssue1681
+}
+
+func (t *ParentIssue1681) MarshalJSON() ([]byte, error) {
+	return []byte(`{"custom":"thing"}`), nil
+}
+
+type ChildIssue1681 struct{}
+
+func (t ChildIssue1681) MarshalJSON() ([]byte, error) {
+	return []byte(`{"someVal": false}`), nil
+}
+
+// https://github.com/jackc/pgx/issues/1681
+func TestJSONCodecEncodeJSONMarshalerThatCanBeWrapped(t *testing.T) {
+	defaultConnTestRunner.RunTest(context.Background(), t, func(ctx context.Context, t testing.TB, conn *pgx.Conn) {
+		var jsonStr string
+		err := conn.QueryRow(context.Background(), "select $1::json", &ParentIssue1681{}).Scan(&jsonStr)
+		require.NoError(t, err)
+		require.Equal(t, `{"custom":"thing"}`, jsonStr)
+	})
+}

pgtype/jsonb_test.go

@@ -70,3 +70,13 @@ func TestJSONBCodecUnmarshalSQLNull(t *testing.T) {
 		require.EqualError(t, err, "can't scan into dest[0]: cannot scan NULL into *int")
 	})
 }
+
+// https://github.com/jackc/pgx/issues/1681
+func TestJSONBCodecEncodeJSONMarshalerThatCanBeWrapped(t *testing.T) {
+	defaultConnTestRunner.RunTest(context.Background(), t, func(ctx context.Context, t testing.TB, conn *pgx.Conn) {
+		var jsonStr string
+		err := conn.QueryRow(context.Background(), "select $1::jsonb", &ParentIssue1681{}).Scan(&jsonStr)
+		require.NoError(t, err)
+		require.Equal(t, `{"custom": "thing"}`, jsonStr) // Note that unlike json, jsonb reformats the JSON string.
+	})
+}