database/sql: permit scanning into interface{}

See thread http://goo.gl/7zzzU for background.

R=rsc
CC=golang-dev
https://golang.org/cl/5624051

src/pkg/database/sql/convert.go

@@ -49,6 +49,11 @@ func convertAssign(dest, src interface{}) error {
 		case *string:
 			*d = string(s)
 			return nil
+		case *interface{}:
+			bcopy := make([]byte, len(s))
+			copy(bcopy, s)
+			*d = bcopy
+			return nil
 		case *[]byte:
 			*d = s
 			return nil
@@ -80,6 +85,9 @@ func convertAssign(dest, src interface{}) error {
 			*d = bv.(bool)
 		}
 		return err
+	case *interface{}:
+		*d = src
+		return nil
 	}
 
 	if scanner, ok := dest.(ScannerInto); ok {

src/pkg/database/sql/convert_test.go

@@ -18,14 +18,15 @@ type conversionTest struct {
 	s, d interface{} // source and destination
 
 	// following are used if they're non-zero
-	wantint  int64
-	wantuint uint64
-	wantstr  string
-	wantf32  float32
-	wantf64  float64
-	wanttime time.Time
-	wantbool bool // used if d is of type *bool
-	wanterr  string
+	wantint   int64
+	wantuint  uint64
+	wantstr   string
+	wantf32   float32
+	wantf64   float64
+	wanttime  time.Time
+	wantbool  bool // used if d is of type *bool
+	wanterr   string
+	wantiface interface{}
 }
 
 // Target variables for scanning into.
@@ -41,6 +42,7 @@ var (
 	scanf32    float32
 	scanf64    float64
 	scantime   time.Time
+	scaniface  interface{}
 )
 
 var conversionTests = []conversionTest{
@@ -95,6 +97,14 @@ var conversionTests = []conversionTest{
 	{s: float64(1.5), d: &scanf32, wantf32: float32(1.5)},
 	{s: "1.5", d: &scanf32, wantf32: float32(1.5)},
 	{s: "1.5", d: &scanf64, wantf64: float64(1.5)},
+
+	// To interface{}
+	{s: float64(1.5), d: &scaniface, wantiface: float64(1.5)},
+	{s: int64(1), d: &scaniface, wantiface: int64(1)},
+	{s: "str", d: &scaniface, wantiface: "str"},
+	{s: []byte("byteslice"), d: &scaniface, wantiface: []byte("byteslice")},
+	{s: true, d: &scaniface, wantiface: true},
+	{s: nil, d: &scaniface},
 }
 
 func intValue(intptr interface{}) int64 {
@@ -152,6 +162,18 @@ func TestConversions(t *testing.T) {
 		if !ct.wanttime.IsZero() && !ct.wanttime.Equal(timeValue(ct.d)) {
 			errf("want time %v, got %v", ct.wanttime, timeValue(ct.d))
 		}
+		if ifptr, ok := ct.d.(*interface{}); ok {
+			if !reflect.DeepEqual(ct.wantiface, scaniface) {
+				errf("want interface %#v, got %#v", ct.wantiface, scaniface)
+				continue
+			}
+			if srcBytes, ok := ct.s.([]byte); ok {
+				dstBytes := (*ifptr).([]byte)
+				if &dstBytes[0] == &srcBytes[0] {
+					errf("copy into interface{} didn't copy []byte data")
+				}
+			}
+		}
 	}
 }
 

src/pkg/database/sql/sql.go

@@ -880,6 +880,10 @@ func (rs *Rows) Columns() ([]string, error) {
 // be modified and held indefinitely. The copy can be avoided by using
 // an argument of type *RawBytes instead; see the documentation for
 // RawBytes for restrictions on its use.
+//
+// If an argument has type *interface{}, Scan copies the value
+// provided by the underlying driver without conversion. If the value
+// is of type []byte, a copy is made and the caller owns the result.
 func (rs *Rows) Scan(dest ...interface{}) error {
 	if rs.closed {
 		return errors.New("sql: Rows closed")