From 7ebced92b53fddc35fc26baad3c4f2fe23013fa9 Mon Sep 17 00:00:00 2001
From: Jacopo <dedalusj@gmail.com>
Date: Fri, 24 Nov 2023 06:22:40 +1100
Subject: [PATCH] Fix issue with order of json encoding #1805

---
 pgtype/json.go      | 15 +++++++++------
 pgtype/json_test.go | 39 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 6 deletions(-)

diff --git a/pgtype/json.go b/pgtype/json.go
index d332dd0d..3f1a750f 100644
--- a/pgtype/json.go
+++ b/pgtype/json.go
@@ -25,18 +25,21 @@ func (c JSONCodec) PlanEncode(m *Map, oid uint32, format int16, value any) Encod
 	case []byte:
 		return encodePlanJSONCodecEitherFormatByteSlice{}
 
+	// Cannot rely on driver.Valuer being handled later because anything can be marshalled.
+	//
+	// https://github.com/jackc/pgx/issues/1430
+	//
+	// Check for driver.Valuer must come before json.Marshaler so that it is guaranteed to beused
+	// when both are implemented https://github.com/jackc/pgx/issues/1805
+	case driver.Valuer:
+		return &encodePlanDriverValuer{m: m, oid: oid, formatCode: format}
+
 	// 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
-	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
diff --git a/pgtype/json_test.go b/pgtype/json_test.go
index b4f35d06..2474fd37 100644
--- a/pgtype/json_test.go
+++ b/pgtype/json_test.go
@@ -3,6 +3,9 @@ package pgtype_test
 import (
 	"context"
 	"database/sql"
+	"database/sql/driver"
+	"encoding/json"
+	"errors"
 	"testing"
 
 	pgx "github.com/jackc/pgx/v5"
@@ -55,6 +58,9 @@ func TestJSONCodec(t *testing.T) {
 
 		// 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})},
+
+		// Test driver.Valuer is used before json.Marshaler (https://github.com/jackc/pgx/issues/1805)
+		{Issue1805(7), new(Issue1805), isExpectedEq(Issue1805(7))},
 	})
 
 	pgxtest.RunValueRoundTripTests(context.Background(), t, defaultConnTestRunner, pgxtest.KnownOIDQueryExecModes, "json", []pgxtest.ValueRoundTripTest{
@@ -68,6 +74,39 @@ func TestJSONCodec(t *testing.T) {
 	})
 }
 
+type Issue1805 int
+
+func (i *Issue1805) Scan(src any) error {
+	var source []byte
+	switch src.(type) {
+	case string:
+		source = []byte(src.(string))
+	case []byte:
+		source = src.([]byte)
+	default:
+		return errors.New("unknown source type")
+	}
+	var newI int
+	if err := json.Unmarshal(source, &newI); err != nil {
+		return err
+	}
+	*i = Issue1805(newI)
+	return nil
+}
+
+func (i Issue1805) Value() (driver.Value, error) {
+	b, err := json.Marshal(int(i))
+	return string(b), err
+}
+
+func (i Issue1805) UnmarshalJSON(bytes []byte) error {
+	return errors.New("UnmarshalJSON called")
+}
+
+func (i Issue1805) MarshalJSON() ([]byte, error) {
+	return nil, errors.New("MarshalJSON called")
+}
+
 // https://github.com/jackc/pgx/issues/1273#issuecomment-1221414648
 func TestJSONCodecUnmarshalSQLNull(t *testing.T) {
 	defaultConnTestRunner.RunTest(context.Background(), t, func(ctx context.Context, t testing.TB, conn *pgx.Conn) {