Address Copilot review comments on codepage support

- Fix nil encoding panic in errorCommand when OutputCodePage is 65001 (UTF-8)
- Close file handle in outCommand when GetEncoding returns an error
- Handle close error properly in errorCommand
- Apply UTF-8 BOM stripping when input codepage is 65001
- Fix test subtest names to use strconv.Itoa instead of string(rune)

Author: dlevy-msft-sql

pkg/sqlcmd/codepage_test.go

@@ -4,6 +4,7 @@
 package sqlcmd
 
 import (
+	"strconv"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -211,7 +212,7 @@ func TestGetEncoding(t *testing.T) {
 	}
 
 	for _, tt := range tests {
-		t.Run(string(rune(tt.codepage)), func(t *testing.T) {
+		t.Run(strconv.Itoa(tt.codepage), func(t *testing.T) {
 			enc, err := GetEncoding(tt.codepage)
 			if tt.wantErr {
 				assert.Error(t, err)

pkg/sqlcmd/commands.go

@@ -330,6 +330,7 @@ func outCommand(s *Sqlcmd, args []string, line uint) error {
 			// Use specified output codepage
 			enc, err := GetEncoding(s.CodePage.OutputCodePage)
 			if err != nil {
+				_ = o.Close()
 				return err
 			}
 			if enc != nil {
@@ -370,11 +371,18 @@ func errorCommand(s *Sqlcmd, args []string, line uint) error {
 		if s.CodePage != nil && s.CodePage.OutputCodePage != 0 {
 			enc, err := GetEncoding(s.CodePage.OutputCodePage)
 			if err != nil {
-				o.Close()
+				if cerr := o.Close(); cerr != nil {
+					return fmt.Errorf("%v; additionally, closing error file %q failed: %w", err, args[0], cerr)
+				}
 				return err
 			}
-			encoder := transform.NewWriter(o, enc.NewEncoder())
-			s.SetError(encoder)
+			if enc == nil {
+				// UTF-8 (or default) encoding: write directly without transform
+				s.SetError(o)
+			} else {
+				encoder := transform.NewWriter(o, enc.NewEncoder())
+				s.SetError(encoder)
+			}
 		} else {
 			s.SetError(o)
 		}

pkg/sqlcmd/sqlcmd.go

@@ -345,8 +345,11 @@ func (s *Sqlcmd) IncludeFile(path string, processAll bool) error {
 		if enc != nil {
 			// Transform from specified encoding to UTF-8
 			reader = transform.NewReader(f, enc.NewDecoder())
+		} else {
+			// UTF-8 codepage: still apply BOM stripping
+			utf8bom := unicode.BOMOverride(unicode.UTF8.NewDecoder())
+			reader = transform.NewReader(f, utf8bom)
 		}
-		// If enc is nil, it's UTF-8, no transformation needed
 	} else {
 		// Default: auto-detect BOM for UTF-16, fallback to UTF-8
 		utf16bom := unicode.BOMOverride(unicode.UTF8.NewDecoder())