Add ERROR_NETNAME_DELETED to IsPathUnreachableError for Windows localhost removal

[Copilot]

Windows removed localhost support in recent updates, causing ERROR_NETNAME_DELETED (0x40/64) when accessing UNC paths like \\LOCALHOST\share\path. This triggers a Debug.Assert failure in FillAttributeInfo because the error code isn't recognized as a path unreachable condition.

Changes

• Interop.Errors.cs: Added ERROR_NETNAME_DELETED = 0x40 constant
• FileSystem.Attributes.Windows.cs: Added ERROR_NETNAME_DELETED to IsPathUnreachableError pattern match

This aligns handling with other network path errors (ERROR_BAD_NETPATH, ERROR_BAD_NET_NAME, etc.) already in the unreachable path list.

Context

if(!IsPathUnreachableError(errorCode)){Debug.Assert(errorCode==ERROR_ACCESS_DENIED||errorCode==ERROR_SHARING_VIOLATION||errorCode==ERROR_SEM_TIMEOUT,$"Unexpected error code getting attributes {errorCode} from path {path}");// ...}

Previously, ERROR_NETNAME_DELETED fell through to the assertion. Now it's handled as unreachable.

Fixes#120380 (possibly same root cause)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>System.IO.Tests fails with "Unexpected error code getting attributes 64 from path \LOCALHOST"</issue_title>
<issue_description>## Build Information
Build: https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_build/results?buildId=1181840
Build error leg or test failing: System.IO.FileSystem.Tests.WorkItemExecution
Pull request: #119878

Error Message

Fill the error message using step by step known issues guidance.

{
"ErrorMessage": "Unexpected error code getting attributes 64 from path \\\\LOCALHOST",
"ErrorPattern": "",
"BuildRetry": false,
"ExcludeConsoleLog": false
}

Known issue validation

Build: 🔎https://dev.azure.com/dnceng-public/public/_build/results?buildId=1181840
Error message validated:[Unexpected error code getting attributes 64 from path \LOCALHOST]
Result validation: ❌ Known issue did not match with the provided build.
Validation performed at: 10/22/2025 2:11:40 PM UTC

Known issue validation

Build: 🔎https://dev.azure.com/dnceng-public/public/_build/results?buildId=1181840
Error message validated:[Unexpected error code getting attributes 64 from path \\LOCALHOST]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 10/22/2025 2:17:17 PM UTC

Report

Build	Definition	Test	Pull Request
1200811	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution
1200758	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution	#121524
1200347	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution	#121524
1200222	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution
1199457	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution
1199150	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution
1198822	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution
1197942	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution
1197801	dotnet/runtime	System.IO.FileSystem.Tests.WorkItemExecution
1197409	dotnet/runtime	[System.IO.FileSys...

• FixesSystem.IO.Tests fails with "Unexpected error code getting attributes 64 from path \\LOCALHOST" #120974

---

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[jkotas]

/azp run runtime-nativeaot-outerloop

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Azure Pipelines successfully started running 1 pipeline(s).

[Copilot]

Pull Request Overview

This PR addresses a bug where Windows' removal of localhost support in recent updates causes ERROR_NETNAME_DELETED (error code 64/0x40) when accessing UNC paths like \\LOCALHOST\share\path. This error was triggering a Debug.Assert failure because it wasn't recognized as a path unreachable condition.

Key Changes:

• Added ERROR_NETNAME_DELETED = 0x40 constant to Interop.Errors.cs
• Added ERROR_NETNAME_DELETED to the IsPathUnreachableError pattern match in FileSystem.Attributes.Windows.cs

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/libraries/Common/src/Interop/Windows/Interop.Errors.cs	Added ERROR_NETNAME_DELETED constant with hex value 0x40, positioned correctly between other network-related error codes
src/libraries/Common/src/System/IO/FileSystem.Attributes.Windows.cs	Added ERROR_NETNAME_DELETED to the IsPathUnreachableError pattern match, grouping it logically with other network path errors

[jozkee]

/ba-g #114315 and

/Users/runner/work/1/s/artifacts/toolset/restore.proj : error : Unable to load the service index for source https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-public/nuget/v3/index.json.

on osx-arm64 Release NativeAOT_Libs.

[jozkee]

/backport to release/10.0

[github-actions]

Started backporting to release/10.0 (link to workflow run)