database/sql: allow drivers to override Scan behavior

src/database/sql/driver/driver.go

@@ -515,6 +515,18 @@ type RowsColumnTypePrecisionScale interface {
  ColumnTypePrecisionScale(index int) (precision, scale int64, ok bool)
 }
 
+// RowsColumnScanner may be implemented by [Rows]. It allows the driver to completely
+// take responsibility for how values are scanned and replace the normal [database/sql].
+// scanning path. This allows drivers to directly support types that do not implement
+// [database/sql.Scanner].
+type RowsColumnScanner interface {
+ Rows
+
+ // ScanColumn copies the column in the current row into the value pointed at by
+ // dest. It returns [ErrSkip] to fall back to the normal [database/sql] scanning path.
+ ScanColumn(index int, dest any) error
+}
+
 // Tx is a transaction.
 type Tx interface {
  Commit() error

src/database/sql/sql.go

@@ -3389,7 +3389,16 @@ func (rs *Rows) Scan(dest ...any) error {
  }
 
  for i, sv := range rs.lastcols {
- err := convertAssignRows(dest[i], sv, rs)
+ err := driver.ErrSkip
+
+ if rowsColumnScanner, ok := rs.rowsi.(driver.RowsColumnScanner); ok {
+ err = rowsColumnScanner.ScanColumn(i, dest[i])
+ }
+
+ if err == driver.ErrSkip {
+ err = convertAssignRows(dest[i], sv, rs)
+ }
+
  if err != nil {
  rs.closemuRUnlockIfHeldByScan()
  return fmt.Errorf(`sql: Scan error on column index %d, name %q: %w`, i, rs.rowsi.Columns()[i], err)