Remove formatter encoding parameter

Co-authored-by: bergmeister <9250262+bergmeister@users.noreply.github.com>

Author: Copilot

Engine/Commands/InvokeFormatterCommand.cs

@@ -65,13 +65,6 @@ public class InvokeFormatterCommand : PSCmdlet, IOutputWriter
         [ValidateCount(4, 4)]
         public int[] Range { get; set; }
 
-        /// <summary>
-        /// The encoding to use when reading files without a byte-order mark.
-        /// </summary>
-        [Parameter(Mandatory = false)]
-        [ValidateNotNullOrEmpty]
-        public string Encoding { get; set; } = "utf-8";
-
 #if DEBUG
         /// <summary>
         /// Attaches to an instance of a .Net debugger
@@ -161,14 +154,22 @@ private void FormatFile(string path)
         {
             Encoding encoding;
             string scriptDefinition;
-            var requestedEncoding = System.Text.Encoding.GetEncoding(
-                Encoding,
-                EncoderFallback.ExceptionFallback,
-                DecoderFallback.ExceptionFallback);
-            using (var reader = new StreamReader(path, requestedEncoding, true))
+            try
+            {
+                using (var reader = new StreamReader(path, new UTF8Encoding(false, true), true))
+                {
+                    scriptDefinition = reader.ReadToEnd();
+                    encoding = reader.CurrentEncoding;
+                }
+            }
+            catch (DecoderFallbackException) when (!HasByteOrderMark(path))
             {
-                scriptDefinition = reader.ReadToEnd();
-                encoding = reader.CurrentEncoding;
+                encoding = GetLegacyFallbackEncoding();
+                using (var reader = new StreamReader(path, encoding, true))
+                {
+                    scriptDefinition = reader.ReadToEnd();
+                    encoding = reader.CurrentEncoding;
+                }
             }
 
             bool inferIndentationKind = inputSettings.RuleArguments.TryGetValue(IndentationRule, out var indentationSettings)
@@ -199,6 +200,39 @@ private void FormatFile(string path)
             WriteObject(formattedScriptDefinition);
         }
 
+        private static bool HasByteOrderMark(string path)
+        {
+            using (var stream = File.OpenRead(path))
+            {
+                int firstByte = stream.ReadByte();
+                int secondByte = stream.ReadByte();
+                int thirdByte = stream.ReadByte();
+                int fourthByte = stream.ReadByte();
+
+                return firstByte == 0xEF && secondByte == 0xBB && thirdByte == 0xBF
+                    || firstByte == 0xFF && secondByte == 0xFE
+                    || firstByte == 0xFE && secondByte == 0xFF
+                    || firstByte == 0x00 && secondByte == 0x00 && thirdByte == 0xFE && fourthByte == 0xFF
+                    || firstByte == 0xFF && secondByte == 0xFE && thirdByte == 0x00 && fourthByte == 0x00;
+            }
+        }
+
+        private static Encoding GetLegacyFallbackEncoding()
+        {
+            if (Encoding.Default.CodePage != 65001)
+            {
+                return Encoding.GetEncoding(
+                    Encoding.Default.CodePage,
+                    EncoderFallback.ExceptionFallback,
+                    DecoderFallback.ExceptionFallback);
+            }
+
+#if CORECLR
+            Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);
+#endif
+            return Encoding.GetEncoding(1252, EncoderFallback.ExceptionFallback, DecoderFallback.ExceptionFallback);
+        }
+
         private static string GetIndentationKind(string scriptDefinition)
         {
             int tabIndentedLines = 0;

Tests/Engine/InvokeFormatter.tests.ps1

@@ -54,14 +54,14 @@ Describe "Invoke-Formatter Cmdlet" {
             [System.IO.File]::ReadAllBytes($path)[0..1] | Should -Be @(255, 254)
         }
 
-        It 'Formats BOM-less files using the specified encoding' {
+        It 'Best-effort formats BOM-less files using a legacy encoding' {
             $path = Join-Path $TestDrive 'legacy-encoding.ps1'
             $scriptDefinition = '$name=''café'''
             $expected = '$name = ''café'''
             $encoding = [System.Text.Encoding]::GetEncoding(1252)
             [System.IO.File]::WriteAllBytes($path, $encoding.GetBytes($scriptDefinition))
 
-            Invoke-Formatter -Path $path -Encoding 'windows-1252' | Should -Be $expected
+            Invoke-Formatter -Path $path | Should -Be $expected
 
             [System.IO.File]::ReadAllBytes($path) | Should -Be $encoding.GetBytes($expected)
         }

docs/Cmdlets/Invoke-Formatter.md

@@ -16,9 +16,9 @@ Formats script text or a file based on the input settings or default settings.
 
 ```
 Invoke-Formatter [-ScriptDefinition] <string> [[-Settings] <Object>] [[-Range] <int[]>]
- [-Encoding <string>] [-WhatIf] [-Confirm] [<CommonParameters>]
+ [-WhatIf] [-Confirm] [<CommonParameters>]
 Invoke-Formatter -Path <string> [[-Settings] <Object>] [[-Range] <int[]>]
- [-Encoding <string>] [-WhatIf] [-Confirm] [<CommonParameters>]
+ [-WhatIf] [-Confirm] [<CommonParameters>]
 ```
 
 ## DESCRIPTION
@@ -28,8 +28,8 @@ The `Invoke-Formatter` cmdlet formats a string input or a file according to defi
 defined in `Settings/CodeFormatting.psd1`. When **Path** is used, the file is formatted in place.
 The file's detected encoding and line-ending style are retained, and the default settings use the
 file's detected tab or space indentation style. Use `-WhatIf` to preview whether a file would be
-changed without writing it. Use **Encoding** to specify the encoding for files without a byte-order
-mark (BOM); a detected BOM takes precedence.
+changed without writing it. BOM-less files are interpreted as UTF-8 when valid; otherwise the system
+ANSI encoding or Windows-1252 is used as a best-effort fallback.
 
 ## EXAMPLES
 
@@ -97,23 +97,6 @@ Invoke-Formatter -Path /path/to/script.ps1
 
 ## PARAMETERS
 
-### -Encoding
-
-The encoding to use when reading and writing files without a byte-order mark (BOM). Files with a BOM
-continue to use the encoding detected from the BOM. The default is UTF-8.
-
-```yaml
-Type: String
-Parameter Sets: (All)
-Aliases:
-
-Required: False
-Position: Named
-Default value: utf-8
-Accept pipeline input: False
-Accept wildcard characters: False
-```
-
 ### -Range
 
 The range within which formatting should take place. The value of this parameter must be an array of