database/sql: additional underlying types in DefaultValueConverter

The previous documentation purported to convert underlying strings to
[]byte, which it did not do. This adds support for underlying bool,
string, and []byte, which convert directly to their underlying type.

Fixes #15174.

Change-Id: I7fc4e2520577f097a48f39c9ff6c8160fdfb7be4
Reviewed-on: https://go-review.googlesource.com/27812Reviewed-by: Daniel Theophanes <kardianos@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>

src/database/sql/driver/types.go

@@ -198,9 +198,9 @@ func IsScanValue(v interface{}) bool {
 // Value method is used to return a Value. As a fallback, the provided
 // argument's underlying type is used to convert it to a Value:
 // underlying integer types are converted to int64, floats to float64,
-// and strings to []byte. If the argument is a nil pointer,
-// ConvertValue returns a nil Value. If the argument is a non-nil
-// pointer, it is dereferenced and ConvertValue is called
+// bool, string, and []byte to themselves. If the argument is a nil
+// pointer, ConvertValue returns a nil Value. If the argument is a
+// non-nil pointer, it is dereferenced and ConvertValue is called
 // recursively. Other types are an error.
 var DefaultParameterConverter defaultConverter
 
@@ -267,6 +267,16 @@ func (defaultConverter) ConvertValue(v interface{}) (Value, error) {
 		return int64(u64), nil
 	case reflect.Float32, reflect.Float64:
 		return rv.Float(), nil
+	case reflect.Bool:
+		return rv.Bool(), nil
+	case reflect.Slice:
+		ek := rv.Type().Elem().Kind()
+		if ek == reflect.Uint8 {
+			return rv.Bytes(), nil
+		}
+		return nil, fmt.Errorf("unsupported type %T, a slice of %s", v, ek)
+	case reflect.String:
+		return rv.String(), nil
 	}
 	return nil, fmt.Errorf("unsupported type %T, a %s", v, rv.Kind())
 }

src/database/sql/driver/types_test.go

@@ -20,6 +20,16 @@ type valueConverterTest struct {
 var now = time.Now()
 var answer int64 = 42
 
+type (
+	i  int64
+	f  float64
+	b  bool
+	bs []byte
+	s  string
+	t  time.Time
+	is []int
+)
+
 var valueConverterTests = []valueConverterTest{
 	{Bool, "true", true, ""},
 	{Bool, "True", true, ""},
@@ -41,6 +51,12 @@ var valueConverterTests = []valueConverterTest{
 	{DefaultParameterConverter, (*int64)(nil), nil, ""},
 	{DefaultParameterConverter, &answer, answer, ""},
 	{DefaultParameterConverter, &now, now, ""},
+	{DefaultParameterConverter, i(9), int64(9), ""},
+	{DefaultParameterConverter, f(0.1), float64(0.1), ""},
+	{DefaultParameterConverter, b(true), true, ""},
+	{DefaultParameterConverter, bs{1}, []byte{1}, ""},
+	{DefaultParameterConverter, s("a"), "a", ""},
+	{DefaultParameterConverter, is{1}, nil, "unsupported type driver.is, a slice of int"},
 }
 
 func TestValueConverters(t *testing.T) {