Fix encode driver.Valuer on nil-able non-pointers

https://github.com/jackc/pgx/issues/1566
https://github.com/jackc/pgx/issues/1860
https://github.com/jackc/pgx/pull/2019#discussion_r1605806751

extended_query_builder.go

@@ -198,6 +198,11 @@ func (eqb *ExtendedQueryBuilder) oidAndArgForQueryExecModeExec(m *pgtype.Map, ar
 		if err != nil {
 			return 0, nil, err
 		}
+
+		if v == nil {
+			return 0, nil, nil
+		}
+
 		if dt, ok := m.TypeForValue(v); ok {
 			return dt.OID, v, nil
 		}

internal/anynil/anynil.go

@@ -14,9 +14,8 @@ import (
 // var valuerReflectType = reflect.TypeFor[driver.Valuer]()
 var valuerReflectType = reflect.TypeOf((*driver.Valuer)(nil)).Elem()
 
-// Is returns true if value is any type of nil except a pointer that directly implements driver.Valuer. e.g. nil,
-// []byte(nil), and a *T where T implements driver.Valuer get normalized to nil but a *T where *T implements
-// driver.Valuer does not.
+// Is returns true if value is any type of nil unless it implements driver.Valuer. *T is not considered to implement
+// driver.Valuer if it is only implemented by T.
 func Is(value any) bool {
 	if value == nil {
 		return true
@@ -30,14 +29,13 @@ func Is(value any) bool {
 			return false
 		}
 
-		if kind == reflect.Ptr {
-			if _, ok := value.(driver.Valuer); ok {
-				// The pointer will be considered to implement driver.Valuer even if it is actually implemented on the value.
-				// But we only want to consider it nil if it is implemented on the pointer. So check if what the pointer points
-				// to implements driver.Valuer.
-				if !refVal.Type().Elem().Implements(valuerReflectType) {
-					return false
-				}
+		if _, ok := value.(driver.Valuer); ok {
+			if kind == reflect.Ptr {
+				// The type assertion will succeed if driver.Valuer is implemented on T or *T. Check if it is implemented on T
+				// to see if it is not implemented on *T.
+				return refVal.Type().Elem().Implements(valuerReflectType)
+			} else {
+				return false
 			}
 		}
 

pgtype/doc.go

@@ -144,10 +144,10 @@ Encoding Typed Nils
 pgtype normalizes typed nils (e.g. []byte(nil)) into nil. nil is always encoded is the SQL NULL value without going
 through the Codec system. This means that Codecs and other encoding logic does not have to handle nil or *T(nil).
 
-However, database/sql compatibility requires Value to be called on a pointer that implements driver.Valuer. See
+However, database/sql compatibility requires Value to be called on T(nil) when T implements driver.Valuer. Therefore,
+driver.Valuer values are not normalized to nil unless it is a *T(nil) where driver.Valuer is implemented on T. See
 https://github.com/golang/go/issues/8415 and
-https://github.com/golang/go/commit/0ce1d79a6a771f7449ec493b993ed2a720917870. Therefore, pointers that implement
-driver.Valuer are not normalized to nil.
+https://github.com/golang/go/commit/0ce1d79a6a771f7449ec493b993ed2a720917870.
 
 Child Records
 

query_test.go

@@ -1173,12 +1173,12 @@ func TestConnQueryDatabaseSQLDriverValuerWithAutoGeneratedPointerReceiver(t *tes
 	ensureConnValid(t, conn)
 }
 
-type nilAsEmptyJSONObject struct {
+type nilPointerAsEmptyJSONObject struct {
 	ID   string
 	Name string
 }
 
-func (v *nilAsEmptyJSONObject) Value() (driver.Value, error) {
+func (v *nilPointerAsEmptyJSONObject) Value() (driver.Value, error) {
 	if v == nil {
 		return "{}", nil
 	}
@@ -1187,7 +1187,7 @@ func (v *nilAsEmptyJSONObject) Value() (driver.Value, error) {
 }
 
 // https://github.com/jackc/pgx/issues/1566
-func TestConnQueryDatabaseSQLDriverValuerCalledOnPointerImplementers(t *testing.T) {
+func TestConnQueryDatabaseSQLDriverValuerCalledOnNilPointerImplementers(t *testing.T) {
 	t.Parallel()
 
 	conn := mustConnectString(t, os.Getenv("PGX_TEST_DATABASE"))
@@ -1195,7 +1195,7 @@ func TestConnQueryDatabaseSQLDriverValuerCalledOnPointerImplementers(t *testing.
 
 	mustExec(t, conn, "create temporary table t(v json not null)")
 
-	var v *nilAsEmptyJSONObject
+	var v *nilPointerAsEmptyJSONObject
 	commandTag, err := conn.Exec(context.Background(), `insert into t(v) values($1)`, v)
 	require.NoError(t, err)
 	require.Equal(t, "INSERT 0 1", commandTag.String())
@@ -1208,12 +1208,119 @@ func TestConnQueryDatabaseSQLDriverValuerCalledOnPointerImplementers(t *testing.
 	_, err = conn.Exec(context.Background(), `delete from t`)
 	require.NoError(t, err)
 
-	v = &nilAsEmptyJSONObject{ID: "1", Name: "foo"}
+	v = &nilPointerAsEmptyJSONObject{ID: "1", Name: "foo"}
 	commandTag, err = conn.Exec(context.Background(), `insert into t(v) values($1)`, v)
 	require.NoError(t, err)
 	require.Equal(t, "INSERT 0 1", commandTag.String())
 
-	var v2 *nilAsEmptyJSONObject
+	var v2 *nilPointerAsEmptyJSONObject
+	err = conn.QueryRow(context.Background(), "select v from t").Scan(&v2)
+	require.NoError(t, err)
+	require.Equal(t, v, v2)
+
+	ensureConnValid(t, conn)
+}
+
+type nilSliceAsEmptySlice []byte
+
+func (j nilSliceAsEmptySlice) Value() (driver.Value, error) {
+	if len(j) == 0 {
+		return []byte("[]"), nil
+	}
+
+	return []byte(j), nil
+}
+
+func (j *nilSliceAsEmptySlice) UnmarshalJSON(data []byte) error {
+	*j = bytes.Clone(data)
+	return nil
+}
+
+// https://github.com/jackc/pgx/issues/1860
+func TestConnQueryDatabaseSQLDriverValuerCalledOnNilSliceImplementers(t *testing.T) {
+	t.Parallel()
+
+	conn := mustConnectString(t, os.Getenv("PGX_TEST_DATABASE"))
+	defer closeConn(t, conn)
+
+	mustExec(t, conn, "create temporary table t(v json not null)")
+
+	var v nilSliceAsEmptySlice
+	commandTag, err := conn.Exec(context.Background(), `insert into t(v) values($1)`, v)
+	require.NoError(t, err)
+	require.Equal(t, "INSERT 0 1", commandTag.String())
+
+	var s string
+	err = conn.QueryRow(context.Background(), "select v from t").Scan(&s)
+	require.NoError(t, err)
+	require.Equal(t, "[]", s)
+
+	_, err = conn.Exec(context.Background(), `delete from t`)
+	require.NoError(t, err)
+
+	v = nilSliceAsEmptySlice(`{"name": "foo"}`)
+	commandTag, err = conn.Exec(context.Background(), `insert into t(v) values($1)`, v)
+	require.NoError(t, err)
+	require.Equal(t, "INSERT 0 1", commandTag.String())
+
+	var v2 nilSliceAsEmptySlice
+	err = conn.QueryRow(context.Background(), "select v from t").Scan(&v2)
+	require.NoError(t, err)
+	require.Equal(t, v, v2)
+
+	ensureConnValid(t, conn)
+}
+
+type nilMapAsEmptyObject map[string]any
+
+func (j nilMapAsEmptyObject) Value() (driver.Value, error) {
+	if j == nil {
+		return []byte("{}"), nil
+	}
+
+	return json.Marshal(j)
+}
+
+func (j *nilMapAsEmptyObject) UnmarshalJSON(data []byte) error {
+	var m map[string]any
+	err := json.Unmarshal(data, &m)
+	if err != nil {
+		return err
+	}
+
+	*j = m
+
+	return nil
+}
+
+// https://github.com/jackc/pgx/pull/2019#discussion_r1605806751
+func TestConnQueryDatabaseSQLDriverValuerCalledOnNilMapImplementers(t *testing.T) {
+	t.Parallel()
+
+	conn := mustConnectString(t, os.Getenv("PGX_TEST_DATABASE"))
+	defer closeConn(t, conn)
+
+	mustExec(t, conn, "create temporary table t(v json not null)")
+
+	var v nilMapAsEmptyObject
+	commandTag, err := conn.Exec(context.Background(), `insert into t(v) values($1)`, v)
+	require.NoError(t, err)
+	require.Equal(t, "INSERT 0 1", commandTag.String())
+
+	var s string
+	err = conn.QueryRow(context.Background(), "select v from t").Scan(&s)
+	require.NoError(t, err)
+	require.Equal(t, "{}", s)
+
+	_, err = conn.Exec(context.Background(), `delete from t`)
+	require.NoError(t, err)
+
+	v = nilMapAsEmptyObject{"name": "foo"}
+	commandTag, err = conn.Exec(context.Background(), `insert into t(v) values($1)`, v)
+	require.NoError(t, err)
+	require.Equal(t, "INSERT 0 1", commandTag.String())
+
+	var v2 nilMapAsEmptyObject
 	err = conn.QueryRow(context.Background(), "select v from t").Scan(&v2)
 	require.NoError(t, err)
 	require.Equal(t, v, v2)