database/sql: implement Scan of time.Time, document, clarify Scan error text

Fixes #9157

Change-Id: Iadf305a172a0ec53ae91e1b2db3f3351691a48ff
Reviewed-on: https://go-review.googlesource.com/18935
Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>

1 files changed, 27 insertions, 4 deletions

diff --git a/src/database/sql/convert.go b/src/database/sql/convert.go
index bba5a8843a..740fd9d6e7 100644
--- a/src/database/sql/convert.go
+++ b/src/database/sql/convert.go
@@ -12,6 +12,7 @@ import (
 	"fmt"
 	"reflect"
 	"strconv"
+	"time"
 )
 
 var errNilPtr = errors.New("destination pointer is nil") // embedded in descriptive error
@@ -127,6 +128,18 @@ func convertAssign(dest, src interface{}) error {
 			*d = s
 			return nil
 		}
+	case time.Time:
+		switch d := dest.(type) {
+		case *string:
+			*d = s.Format(time.RFC3339Nano)
+			return nil
+		case *[]byte:
+			if d == nil {
+				return errNilPtr
+			}
+			*d = []byte(s.Format(time.RFC3339Nano))
+			return nil
+		}
 	case nil:
 		switch d := dest.(type) {
 		case *interface{}:
@@ -226,7 +239,8 @@ func convertAssign(dest, src interface{}) error {
 		s := asString(src)
 		i64, err := strconv.ParseInt(s, 10, dv.Type().Bits())
 		if err != nil {
-			return fmt.Errorf("converting string %q to a %s: %v", s, dv.Kind(), err)
+			err = strconvErr(err)
+			return fmt.Errorf("converting driver.Value type %T (%q) to a %s: %v", src, s, dv.Kind(), err)
 		}
 		dv.SetInt(i64)
 		return nil
@@ -234,7 +248,8 @@ func convertAssign(dest, src interface{}) error {
 		s := asString(src)
 		u64, err := strconv.ParseUint(s, 10, dv.Type().Bits())
 		if err != nil {
-			return fmt.Errorf("converting string %q to a %s: %v", s, dv.Kind(), err)
+			err = strconvErr(err)
+			return fmt.Errorf("converting driver.Value type %T (%q) to a %s: %v", src, s, dv.Kind(), err)
 		}
 		dv.SetUint(u64)
 		return nil
@@ -242,13 +257,21 @@ func convertAssign(dest, src interface{}) error {
 		s := asString(src)
 		f64, err := strconv.ParseFloat(s, dv.Type().Bits())
 		if err != nil {
-			return fmt.Errorf("converting string %q to a %s: %v", s, dv.Kind(), err)
+			err = strconvErr(err)
+			return fmt.Errorf("converting driver.Value type %T (%q) to a %s: %v", src, s, dv.Kind(), err)
 		}
 		dv.SetFloat(f64)
 		return nil
 	}
 
-	return fmt.Errorf("unsupported driver -> Scan pair: %T -> %T", src, dest)
+	return fmt.Errorf("unsupported Scan, storing driver.Value type %T into type %T", src, dest)
+}
+
+func strconvErr(err error) error {
+	if ne, ok := err.(*strconv.NumError); ok {
+		return ne.Err
+	}
+	return err
 }
 
 func cloneBytes(b []byte) []byte {