Fix the list view to not leak VT decorations (PowerShell#17262)

Author: daxian-dbw

src/System.Management.Automation/FormatAndOutput/common/ListWriter.cs

@@ -6,6 +6,7 @@
 using System.Diagnostics;
 using System.Management.Automation;
 using System.Management.Automation.Internal;
+using System.Text;
 
 namespace Microsoft.PowerShell.Commands.Internal.Format
 {
@@ -30,6 +31,11 @@ internal class ListWriter
         /// </summary>
         private int _columnWidth = 0;
 
+        /// <summary>
+        /// A cached string builder used within this type to reduce creation of temporary strings.
+        /// </summary>
+        private readonly StringBuilder _cachedBuilder = new();
+
         /// <summary>
         /// </summary>
         /// <param name="propertyNames">Names of the properties to display.</param>
@@ -207,7 +213,9 @@ private void WriteProperty(int k, string propertyValue, LineOutput lo)
         private void WriteSingleLineHelper(string prependString, string line, LineOutput lo)
         {
             if (line == null)
+            {
                 line = string.Empty;
+            }
 
             // compute the width of the field for the value string (in screen cells)
             int fieldCellCount = _columnWidth - _propertyLabelsDisplayLength;
@@ -221,14 +229,30 @@ private void WriteSingleLineHelper(string prependString, string line, LineOutput
             // display the string collection
             for (int k = 0; k < sc.Count; k++)
             {
+                string str = sc[k];
+                _cachedBuilder.Clear();
+
                 if (k == 0)
                 {
-                    lo.WriteLine(PSStyle.Instance.Formatting.FormatAccent + prependString + PSStyle.Instance.Reset + sc[k]);
+                    _cachedBuilder
+                        .Append(PSStyle.Instance.Formatting.FormatAccent)
+                        .Append(prependString)
+                        .Append(PSStyle.Instance.Reset)
+                        .Append(str);
                 }
                 else
                 {
-                    lo.WriteLine(padding + PSStyle.Instance.Formatting.FormatAccent + PSStyle.Instance.Reset + sc[k]);
+                    _cachedBuilder
+                        .Append(padding)
+                        .Append(str);
                 }
+
+                if (str.Contains(ValueStringDecorated.ESC) && !str.EndsWith(PSStyle.Instance.Reset))
+                {
+                    _cachedBuilder.Append(PSStyle.Instance.Reset);
+                }
+
+                lo.WriteLine(_cachedBuilder.ToString());
             }
         }
 

test/powershell/Modules/Microsoft.PowerShell.Utility/Format-List.Tests.ps1

@@ -229,4 +229,17 @@ Describe 'Format-List color tests' {
         $out[0] | Should -BeExactly "$($PSStyle.Formatting.FormatAccent)Short      : $($PSStyle.Reset)1" -Because ($out[0] | Format-Hex)
         $out[1] | Should -BeExactly "$($PSStyle.Formatting.FormatAccent)LongLabelN : $($PSStyle.Reset)2"
     }
+
+    It 'VT decorations in a property value should not be leaked in list view' {
+        $expected = @"
+`e[32;1ma : `e[0mHello
+`e[32;1mb : `e[0m`e[36mworld`e[0m
+"@
+        ## Format-List should append the 'reset' escape sequence to the value of 'b' property.
+        $obj = [pscustomobject]@{ a = "Hello"; b = $PSStyle.Foreground.Cyan + "world"; }
+        $obj | Format-List | Out-File "$TestDrive/outfile.txt"
+
+        $output = Get-Content "$TestDrive/outfile.txt" -Raw
+        $output.Trim().Replace("`r", "") | Should -BeExactly $expected.Replace("`r", "")
+    }
 }