Fix the inverted reparse point filter in the netstandard2.0 cleanup path (#3255)

FileCleanupHelper's netstandard2.0 enumeration kept only the entries whose
ReparsePoint attribute was set, the opposite of the AttributesToSkip the
other branch passes. On a .NET Framework host that left every regular file
in place, so the recursive Delete then threw into TryExecute's empty catch
and the work directory survived - the cleanup #3175 added never ran there.

A stale directory is not inert: the generated project imports files it finds
beside itself, so leftovers from an earlier run can be picked up by the next
one.

The tests cover both the file and the directory entry points; the two
directory cases fail on net472 without this fix.

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

Author: timcassell

src/BenchmarkDotNet/Helpers/FileCleanupHelper.cs

@@ -61,7 +61,7 @@ private static IEnumerable<FileInfo> EnumerateFiles(DirectoryInfo directory)
         try
         {
             return directory.EnumerateFiles("*", SearchOption.TopDirectoryOnly)
-                            .Where(x => (x.Attributes & FileAttributes.ReparsePoint) != 0);
+                            .Where(x => (x.Attributes & FileAttributes.ReparsePoint) == 0);
         }
         catch
         {
@@ -75,7 +75,7 @@ private static IEnumerable<DirectoryInfo> EnumerateSubDirectories(DirectoryInfo
         try
         {
             return directory.EnumerateDirectories()
-                            .Where(x => (x.Attributes & FileAttributes.ReparsePoint) != 0);
+                            .Where(x => (x.Attributes & FileAttributes.ReparsePoint) == 0);
         }
         catch
         {

tests/BenchmarkDotNet.Tests/Helpers/FileCleanupHelperTests.cs

@@ -0,0 +1,72 @@
+using AwesomeAssertions;
+using BenchmarkDotNet.Helpers;
+
+namespace BenchmarkDotNet.Tests.Helpers;
+
+public class FileCleanupHelperTests : IDisposable
+{
+    private readonly string rootPath = Path.Combine(Path.GetTempPath(), $"BDN.FileCleanupHelperTests.{Guid.NewGuid():N}");
+
+    public void Dispose()
+    {
+        if (!Directory.Exists(rootPath))
+            return;
+
+        foreach (var file in Directory.EnumerateFiles(rootPath, "*", SearchOption.AllDirectories))
+            File.SetAttributes(file, FileAttributes.Normal);
+
+        Directory.Delete(rootPath, recursive: true);
+    }
+
+    [Fact]
+    public void CleanupRemovesFile()
+    {
+        var filePath = CreateFile(rootPath, "program.notcs");
+
+        FileCleanupHelper.Cleanup(filePath);
+
+        File.Exists(filePath).Should().BeFalse();
+    }
+
+    [Fact]
+    public void CleanupRemovesReadOnlyFile()
+    {
+        var filePath = CreateFile(rootPath, "readonly.txt");
+        File.SetAttributes(filePath, FileAttributes.ReadOnly);
+
+        FileCleanupHelper.Cleanup(filePath);
+
+        File.Exists(filePath).Should().BeFalse();
+    }
+
+    [Fact]
+    public void CleanupRemovesDirectoryWithItsContents()
+    {
+        CreateFile(rootPath, "BenchmarkDotNet.Autogenerated.csproj");
+        CreateFile(Path.Combine(rootPath, "obj"), "project.assets.json");
+        CreateFile(Path.Combine(rootPath, "obj", "release_net10.0"), "program.dll");
+
+        FileCleanupHelper.Cleanup(rootPath);
+
+        Directory.Exists(rootPath).Should().BeFalse();
+    }
+
+    [Fact]
+    public void CleanupRemovesDirectoryContainingReadOnlyFile()
+    {
+        File.SetAttributes(CreateFile(rootPath, "readonly.txt"), FileAttributes.ReadOnly);
+
+        FileCleanupHelper.Cleanup(rootPath);
+
+        Directory.Exists(rootPath).Should().BeFalse();
+    }
+
+    private static string CreateFile(string directoryPath, string fileName)
+    {
+        Directory.CreateDirectory(directoryPath);
+
+        var filePath = Path.Combine(directoryPath, fileName);
+        File.WriteAllText(filePath, "content");
+        return filePath;
+    }
+}