Remove const insertSelectPlaceholder and associated dead code

insertSelectPlaceholder is an unexported const set at true. No code changes this nor can
any build environment change it.

Therefore we should remove it and the associated dead code.

Signed-off-by: Andrew Thornton <art27@cantab.net>

internal/statements/statement_args.go

@@ -5,78 +5,10 @@
 package statements
 
 import (
-	"fmt"
-	"reflect"
-	"strings"
-	"time"
-
 	"xorm.io/builder"
 	"xorm.io/xorm/schemas"
 )
 
-func quoteNeeded(a interface{}) bool {
-	switch a.(type) {
-	case int, int8, int16, int32, int64:
-		return false
-	case uint, uint8, uint16, uint32, uint64:
-		return false
-	case float32, float64:
-		return false
-	case bool:
-		return false
-	case string:
-		return true
-	case time.Time, *time.Time:
-		return true
-	case builder.Builder, *builder.Builder:
-		return false
-	}
-
-	t := reflect.TypeOf(a)
-	switch t.Kind() {
-	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
-		return false
-	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
-		return false
-	case reflect.Float32, reflect.Float64:
-		return false
-	case reflect.Bool:
-		return false
-	case reflect.String:
-		return true
-	}
-
-	return true
-}
-
-func convertStringSingleQuote(arg string) string {
-	return "'" + strings.Replace(arg, "'", "''", -1) + "'"
-}
-
-func convertString(arg string) string {
-	var buf strings.Builder
-	buf.WriteRune('\'')
-	for _, c := range arg {
-		if c == '\\' || c == '\'' {
-			buf.WriteRune('\\')
-		}
-		buf.WriteRune(c)
-	}
-	buf.WriteRune('\'')
-	return buf.String()
-}
-
-func convertArg(arg interface{}, convertFunc func(string) string) string {
-	if quoteNeeded(arg) {
-		argv := fmt.Sprintf("%v", arg)
-		return convertFunc(argv)
-	}
-
-	return fmt.Sprintf("%v", arg)
-}
-
-const insertSelectPlaceHolder = true
-
 // WriteArg writes an arg
 func (statement *Statement) WriteArg(w *builder.BytesWriter, arg interface{}) error {
 	switch argv := arg.(type) {
@@ -91,7 +23,6 @@ func (statement *Statement) WriteArg(w *builder.BytesWriter, arg interface{}) er
 			return err
 		}
 	default:
-		if insertSelectPlaceHolder {
 		if err := w.WriteByte('?'); err != nil {
 			return err
 		}
@@ -104,15 +35,6 @@ func (statement *Statement) WriteArg(w *builder.BytesWriter, arg interface{}) er
 		} else {
 			w.Append(arg)
 		}
-		} else {
-			var convertFunc = convertStringSingleQuote
-			if statement.dialect.URI().DBType == schemas.MYSQL {
-				convertFunc = convertString
-			}
-			if _, err := w.WriteString(convertArg(arg, convertFunc)); err != nil {
-				return err
-			}
-		}
 	}
 	return nil
 }