Revert "database/sql: allow drivers to override Scan behavior"

This reverts CL 588435.

This new API is difficult to use correctly, and in many cases cannot
be used efficiently. We're going to work on this problem a bit more.

The release notes are removed by CL 729340, since they were moved to
the x/website repository since the original CL was made.

Reopens #67546.

Change-Id: I2a2bd25f2fce5f02e4d28cd33a9cc651bf35ab50
Reviewed-on: https://go-review.googlesource.com/c/go/+/729360
Reviewed-by: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Sean Liao <sean@liao.dev>

3 files changed, 1 insertions, 118 deletions

diff --git a/src/database/sql/driver/driver.go b/src/database/sql/driver/driver.go
index 487870be63..d0892e80fc 100644
--- a/src/database/sql/driver/driver.go
+++ b/src/database/sql/driver/driver.go
@@ -515,18 +515,6 @@ 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(dest any, index int) error
-}
-
 // Tx is a transaction.
 type Tx interface {
 	Commit() error
diff --git a/src/database/sql/sql.go b/src/database/sql/sql.go
index 85b9ffc37d..4be450ca87 100644
--- a/src/database/sql/sql.go
+++ b/src/database/sql/sql.go
@@ -3396,16 +3396,7 @@ func (rs *Rows) scanLocked(dest ...any) error {
 	}
 
 	for i, sv := range rs.lastcols {
-		err := driver.ErrSkip
-
-		if rcs, ok := rs.rowsi.(driver.RowsColumnScanner); ok {
-			err = rcs.ScanColumn(dest[i], i)
-		}
-
-		if err == driver.ErrSkip {
-			err = convertAssignRows(dest[i], sv, rs)
-		}
-
+		err := convertAssignRows(dest[i], sv, rs)
 		if err != nil {
 			return fmt.Errorf(`sql: Scan error on column index %d, name %q: %w`, i, rs.rowsi.Columns()[i], err)
 		}
diff --git a/src/database/sql/sql_test.go b/src/database/sql/sql_test.go
index 6ee8505855..e8a6560097 100644
--- a/src/database/sql/sql_test.go
+++ b/src/database/sql/sql_test.go
@@ -4200,102 +4200,6 @@ func TestNamedValueCheckerSkip(t *testing.T) {
 	}
 }
 
-type rcsDriver struct {
-	fakeDriver
-}
-
-func (d *rcsDriver) Open(dsn string) (driver.Conn, error) {
-	c, err := d.fakeDriver.Open(dsn)
-	fc := c.(*fakeConn)
-	fc.db.allowAny = true
-	return &rcsConn{fc}, err
-}
-
-type rcsConn struct {
-	*fakeConn
-}
-
-func (c *rcsConn) PrepareContext(ctx context.Context, q string) (driver.Stmt, error) {
-	stmt, err := c.fakeConn.PrepareContext(ctx, q)
-	if err != nil {
-		return stmt, err
-	}
-	return &rcsStmt{stmt.(*fakeStmt)}, nil
-}
-
-type rcsStmt struct {
-	*fakeStmt
-}
-
-func (s *rcsStmt) QueryContext(ctx context.Context, args []driver.NamedValue) (driver.Rows, error) {
-	rows, err := s.fakeStmt.QueryContext(ctx, args)
-	if err != nil {
-		return rows, err
-	}
-	return &rcsRows{rows.(*rowsCursor)}, nil
-}
-
-type rcsRows struct {
-	*rowsCursor
-}
-
-func (r *rcsRows) ScanColumn(dest any, index int) error {
-	switch d := dest.(type) {
-	case *int64:
-		*d = 42
-		return nil
-	}
-
-	return driver.ErrSkip
-}
-
-func TestRowsColumnScanner(t *testing.T) {
-	Register("RowsColumnScanner", &rcsDriver{})
-	db, err := Open("RowsColumnScanner", "")
-	if err != nil {
-		t.Fatal(err)
-	}
-	defer db.Close()
-
-	ctx, cancel := context.WithCancel(context.Background())
-	defer cancel()
-
-	_, err = db.ExecContext(ctx, "CREATE|t|str=string,n=int64")
-	if err != nil {
-		t.Fatal("exec create", err)
-	}
-
-	_, err = db.ExecContext(ctx, "INSERT|t|str=?,n=?", "foo", int64(1))
-	if err != nil {
-		t.Fatal("exec insert", err)
-	}
-	var (
-		str string
-		i64 int64
-		i   int
-		f64 float64
-		ui  uint
-	)
-	err = db.QueryRowContext(ctx, "SELECT|t|str,n,n,n,n|").Scan(&str, &i64, &i, &f64, &ui)
-	if err != nil {
-		t.Fatal("select", err)
-	}
-
-	list := []struct{ got, want any }{
-		{str, "foo"},
-		{i64, int64(42)},
-		{i, int(1)},
-		{f64, float64(1)},
-		{ui, uint(1)},
-	}
-
-	for index, item := range list {
-		if !reflect.DeepEqual(item.got, item.want) {
-			t.Errorf("got %#v wanted %#v for index %d", item.got, item.want, index)
-		}
-	}
-}
-
 func TestOpenConnector(t *testing.T) {
 	Register("testctx", &fakeDriverCtx{})
 	db, err := Open("testctx", "people")