Remove const insertSelectPlaceholder and associated dead code (#2151)

`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.

Close #2146

Signed-off-by: Andrew Thornton <art27@cantab.net>
Reviewed-on: https://gitea.com/xorm/xorm/pulls/2151
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Andrew Thornton <art27@cantab.net>
Co-committed-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
 }