Special case the underlying type of []byte

Underlying types were already tried. But []byte is not a normal
underlying type. It is a slice. But since is can be treated as a scalar
instead of an array / slice we need to special case it.

#1763

pgtype/pgtype.go

@@ -1358,6 +1358,8 @@ var kindToTypes map[reflect.Kind]reflect.Type = map[reflect.Kind]reflect.Type{
 	reflect.Bool:    reflect.TypeOf(false),
 }
 
+var byteSliceType = reflect.TypeOf([]byte{})
+
 type underlyingTypeEncodePlan struct {
 	nextValueType reflect.Type
 	next          EncodePlan
@@ -1372,6 +1374,10 @@ func (plan *underlyingTypeEncodePlan) Encode(value any, buf []byte) (newBuf []by
 // TryWrapFindUnderlyingTypeEncodePlan tries to convert to a Go builtin type. e.g. If value was of type MyString and
 // MyString was defined as a string then a wrapper plan would be returned that converts MyString to string.
 func TryWrapFindUnderlyingTypeEncodePlan(value any) (plan WrappedEncodePlanNextSetter, nextValue any, ok bool) {
+	if value == nil {
+		return nil, nil, false
+	}
+
 	if _, ok := value.(driver.Valuer); ok {
 		return nil, nil, false
 	}
@@ -1387,6 +1393,15 @@ func TryWrapFindUnderlyingTypeEncodePlan(value any) (plan WrappedEncodePlanNextS
 		return &underlyingTypeEncodePlan{nextValueType: nextValueType}, refValue.Convert(nextValueType).Interface(), true
 	}
 
+	// []byte is a special case. It is a slice but we treat it as a scalar type. In the case of a named type like
+	// json.RawMessage which is defined as []byte the underlying type should be considered as []byte. But any other slice
+	// does not have a special underlying type.
+	//
+	// https://github.com/jackc/pgx/issues/1763
+	if refValue.Type() != byteSliceType && refValue.Type().AssignableTo(byteSliceType) {
+		return &underlyingTypeEncodePlan{nextValueType: byteSliceType}, refValue.Convert(byteSliceType).Interface(), true
+	}
+
 	return nil, nil, false
 }
 

pgtype/pgtype_test.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"database/sql"
 	"database/sql/driver"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"net"
@@ -417,6 +418,14 @@ func TestMapEncodeByteSliceIntoUnregisteredTypeTextFormat(t *testing.T) {
 	require.Equal(t, []byte(`\x00010203`), buf)
 }
 
+// https://github.com/jackc/pgx/issues/1763
+func TestMapEncodeNamedTypeOfByteSliceIntoTextTextFormat(t *testing.T) {
+	m := pgtype.NewMap()
+	buf, err := m.Encode(pgtype.TextOID, pgtype.TextFormatCode, json.RawMessage(`{"foo": "bar"}`), nil)
+	require.NoError(t, err)
+	require.Equal(t, []byte(`{"foo": "bar"}`), buf)
+}
+
 // https://github.com/jackc/pgx/issues/1326
 func TestMapScanPointerToRenamedType(t *testing.T) {
 	srcBuf := []byte("foo")