Fix pgtype types that can Set database/sql/driver.driver.Valuer

Bug was chooseParameterFormatCode would see that type could handle
binary format so binary format would be chosen. But
encodePreparedStatementArgument would see driver.Valuer first and
would encode with that -- which is text mode. So the server would
receive a text format value when expecting a binary format value.

Discovered while investigating #316

query_test.go

@@ -11,6 +11,8 @@ import (
 
 	"github.com/jackc/pgx"
 	"github.com/jackc/pgx/pgtype"
+	satori "github.com/jackc/pgx/pgtype/ext/satori-uuid"
+	"github.com/satori/go.uuid"
 	"github.com/shopspring/decimal"
 )
 
@@ -855,7 +857,7 @@ func TestQueryRowExErrorsWrongParameterOIDs(t *testing.T) {
 		context.Background(),
 		sql,
 		&pgx.QueryExOptions{
-			ParameterOIDs: paramOIDs,
+			ParameterOIDs:     paramOIDs,
 			ResultFormatCodes: []int16{pgx.BinaryFormatCode},
 		},
 		queryArgs...,
@@ -1000,6 +1002,36 @@ func TestConnQueryDatabaseSQLDriverValuer(t *testing.T) {
 	ensureConnValid(t, conn)
 }
 
+func TestConnQueryDatabaseSQLDriverValuerWithBinaryPgTypeThatAcceptsSameType(t *testing.T) {
+	t.Parallel()
+
+	conn := mustConnect(t, *defaultConnConfig)
+	defer closeConn(t, conn)
+
+	conn.ConnInfo.RegisterDataType(pgtype.DataType{
+		Value: &satori.UUID{},
+		Name:  "uuid",
+		OID:   2950,
+	})
+
+	expected, err := uuid.FromString("6ba7b810-9dad-11d1-80b4-00c04fd430c8")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var u2 uuid.UUID
+	err = conn.QueryRow("select $1::uuid", expected).Scan(&u2)
+	if err != nil {
+		t.Fatalf("Scan failed: %v", err)
+	}
+
+	if expected != u2 {
+		t.Errorf("Expected u2 to be %v, but it was %v", expected, u2)
+	}
+
+	ensureConnValid(t, conn)
+}
+
 func TestConnQueryDatabaseSQLNullX(t *testing.T) {
 	t.Parallel()
 

values.go

@@ -128,12 +128,6 @@ func encodePreparedStatementArgument(ci *pgtype.ConnInfo, buf []byte, oid pgtype
 			pgio.SetInt32(buf[sp:], int32(len(buf[sp:])-4))
 		}
 		return buf, nil
-	case driver.Valuer:
-		v, err := arg.Value()
-		if err != nil {
-			return nil, err
-		}
-		return encodePreparedStatementArgument(ci, buf, oid, v)
 	case string:
 		buf = pgio.AppendInt32(buf, int32(len(arg)))
 		buf = append(buf, arg...)
@@ -154,6 +148,16 @@ func encodePreparedStatementArgument(ci *pgtype.ConnInfo, buf []byte, oid pgtype
 		value := dt.Value
 		err := value.Set(arg)
 		if err != nil {
+			{
+				if arg, ok := arg.(driver.Valuer); ok {
+					v, err := arg.Value()
+					if err != nil {
+						return nil, err
+					}
+					return encodePreparedStatementArgument(ci, buf, oid, v)
+				}
+			}
+
 			return nil, err
 		}
 
@@ -170,6 +174,14 @@ func encodePreparedStatementArgument(ci *pgtype.ConnInfo, buf []byte, oid pgtype
 		return buf, nil
 	}
 
+	if arg, ok := arg.(driver.Valuer); ok {
+		v, err := arg.Value()
+		if err != nil {
+			return nil, err
+		}
+		return encodePreparedStatementArgument(ci, buf, oid, v)
+	}
+
 	if strippedArg, ok := stripNamedType(&refVal); ok {
 		return encodePreparedStatementArgument(ci, buf, oid, strippedArg)
 	}