Add tests to validate we don't fall over enumerating files that just … (#23528)

* Add tests to validate we don't fall over enumerating files that just cross the legacy MAX_PATH barrier. As we do special logic on Windows to support long paths this is an important boundary to test. While these path lengths don't have special meaning outside of Windows, we'll always run them they should still pass .

* Conditionalize tests for long path support

NetFX needs to have the long path functionality enabled to run these
tests.

1 files changed, 39 insertions, 1 deletions

diff --git a/src/System.IO.FileSystem/tests/Directory/GetFiles.cs b/src/System.IO.FileSystem/tests/Directory/GetFiles.cs
index 3c4724334f..79c22762df 100644
--- a/src/System.IO.FileSystem/tests/Directory/GetFiles.cs
+++ b/src/System.IO.FileSystem/tests/Directory/GetFiles.cs
@@ -3,7 +3,6 @@
 // See the LICENSE file in the project root for more information.
 
 using System.Linq;
-using System.Runtime.InteropServices;
 using Xunit;
 
 namespace System.IO.Tests
@@ -42,6 +41,45 @@ namespace System.IO.Tests
             File.Delete(linkPath);
             Assert.Equal(0, GetEntries(containingFolder.FullName).Count());
         }
+
+        [ConditionalFact(nameof(AreAllLongPathsAvailable))]
+        public void EnumerateFilesOverLegacyMaxPath()
+        {
+            // We want to test that directories under the legacy MAX_PATH (260 characters, including the null) can iterate files
+            // even if the full path is over 260.
+
+            string directory = IOServices.GetPath(GetTestFilePath(), 250);
+            Assert.Equal(250, directory.Length);
+            Assert.True(Directory.CreateDirectory(directory).Exists);
+
+            for (int i = 0; i < 6; i++)
+            {
+                string testFile = Path.Combine(directory, new string((char)('0' + i), i + 7));
+                File.Create(testFile).Dispose();
+            }
+
+            string[] files = GetEntries(directory);
+            Assert.Equal(6, files.Length);
+        }
+
+        [ConditionalFact(nameof(AreAllLongPathsAvailable))]
+        public void EnumerateFilesDirectoryOverLegacyMaxPath()
+        {
+            // Check enumerating when the entire path is over MAX_PATH
+
+            string directory = IOServices.GetPath(GetTestFilePath(), 270);
+            Assert.Equal(270, directory.Length);
+            Assert.True(Directory.CreateDirectory(directory).Exists);
+
+            for (int i = 0; i < 6; i++)
+            {
+                string testFile = Path.Combine(directory, new string((char)('0' + i), i + 7));
+                File.Create(testFile).Dispose();
+            }
+
+            string[] files = GetEntries(directory);
+            Assert.Equal(6, files.Length);
+        }
     }
 
     public class Directory_GetFiles_str_str : Directory_GetFileSystemEntries_str_str