Fix encode to json ignoring driver.Valuer

https://github.com/jackc/pgx/issues/1430

pgtype/json.go

@@ -24,6 +24,12 @@ func (c JSONCodec) PlanEncode(m *Map, oid uint32, format int16, value any) Encod
 		return encodePlanJSONCodecEitherFormatString{}
 	case []byte:
 		return encodePlanJSONCodecEitherFormatByteSlice{}
+
+	// Cannot rely on driver.Valuer being handled later because anything can be marshalled.
+	//
+	// https://github.com/jackc/pgx/issues/1430
+	case driver.Valuer:
+		return &encodePlanDriverValuer{m: m, oid: oid, formatCode: format}
 	}
 
 	// Because anything can be marshalled the normal wrapping in Map.PlanScan doesn't get a chance to run. So try the

pgtype/json_test.go

@@ -52,6 +52,9 @@ func TestJSONCodec(t *testing.T) {
 
 		// Test sql.Scanner. (https://github.com/jackc/pgx/issues/1418)
 		{"42", new(sql.NullInt64), isExpectedEq(sql.NullInt64{Int64: 42, Valid: true})},
+
+		// Test driver.Valuer. (https://github.com/jackc/pgx/issues/1430)
+		{sql.NullInt64{Int64: 42, Valid: true}, new(sql.NullInt64), isExpectedEq(sql.NullInt64{Int64: 42, Valid: true})},
 	})
 
 	pgxtest.RunValueRoundTripTests(context.Background(), t, defaultConnTestRunner, pgxtest.KnownOIDQueryExecModes, "json", []pgxtest.ValueRoundTripTest{