PR Summary

AllowHiddenAttribute to be applied to classes and exclude hidden classes from type name completion.

PR Context

Fixes#18914

TheHiddenAttribute can be applied to properties, methods, and other members to hide them from tab completion andGet-Member, but could not be applied to classes themselves. This PR extends the attribute to support classes and ensures hidden classes are excluded from type name completion.

Before this fix:

[Hidden]// Error: Not valid on this declaration typepublicclassInternalHelperClass{}

After this fix:

[Hidden]// Now works - class is hidden from completionpublicclassInternalHelperClass{}varobj=newInternalHelperClass();// Can still instantiate explicitly[Internal<Tab>]// Does NOT suggest InternalHelperClass

PR Checklist

• PR has a meaningful title
• Summarized changes
• Make sure all.h,.cpp,.cs,.ps1 and.psm1 files have the correct copyright header
• This PR is ready to merge and is notWork in Progress
• Breaking changes
  • None
• User-facing changes
  • Documentation needed
    • Issue filed:
• Testing - New and feature
  • Make sure you've added a new test if existing tests do not effectively test the code changed

Description

Implementation

1. ExtendedHiddenAttribute target (Attributes.cs)

• AddedAttributeTargets.Class toAttributeUsage

2. AddedIsHidden property toTypeDefinitionAst (ast.cs)

• Cached property following the same pattern asPropertyMemberAst.IsHidden
• UsesGetReflectionAttributeType() for attribute checking

3. Filtered hidden classes from type completion (CompletionCompleters.cs)

• PowerShell-defined types: Filter using!ast.IsHidden
• C#-defined types: Filter usingtype.IsDefined(typeof(HiddenAttribute), false)

Files Changed

• src/System.Management.Automation/engine/Attributes.cs - Extended AttributeUsage
• src/System.Management.Automation/engine/parser/ast.cs - Added IsHidden property
• src/System.Management.Automation/engine/CommandCompletion/CompletionCompleters.cs - Filter hidden types
• test/powershell/Language/Classes/Scripting.Classes.BasicParsing.Tests.ps1 - Added tests

Testing

Test Coverage

Added 3 comprehensive test cases:

1. Instance creation - Verifies hidden classes can be instantiated
2. Attribute presence - Validates attribute is correctly applied
3. Type completion exclusion - Confirms hidden classes don't appear in tab completion

Results

Describing HiddenAttribute on Class Test  [+] Should be able to create an instance of hidden class 7ms  [+] HiddenAttribute should be present on the class 14ms  [+] Hidden class should not appear in type name completion 142msTests Passed: 327, Failed: 0, Skipped: 11, Pending: 13, Inconclusive: 0

Additional Notes

• No breaking changes - only adds new functionality
• Consistent with existingHiddenAttribute behavior for members
• Performance: Attribute check is cached to avoid repeated reflection calls
• Useful for hiding internal helper classes in modules