Fix NullReferenceException in CompleteFilename when called with empty string #26286

Copilot · 2025-10-23T05:49:45Z

Explore and understand the issue in CompletionCompleters.cs
Identify the root cause (RelatedAsts null reference at line 4583)
Implement fix to handle null RelatedAsts
Add Pester test to verify the fix
Run test to verify fix works correctly
Run CodeQL security scan (no issues found)
Move test to TabCompletion.Tests.ps1 per review feedback
Remove comments from test per review feedback

Summary

Fixed NullReferenceException when calling [System.Management.Automation.CompletionCompleters]::CompleteFilename("").

Root Cause

The public API CompleteFilename(string fileName) creates a CompletionContext with RelatedAsts set to null. The internal method tried to access context.RelatedAsts[^1] without checking for null, causing the exception.

Fix

Added null/empty check for context.RelatedAsts before accessing it. When null or empty, falls back to using context.ExecutionContext.SessionState.Internal.CurrentLocation.ProviderPath.

Test

Added Pester test in TabCompletion.Tests.ps1 that verifies:

CompleteFilename("") doesn't throw exception
Returns valid completion results

Original prompt

This section details on the original issue you should resolve

<issue_title>[System.Management.Automation.CompletionCompleters]::CompleteFilename("") throws NullReferenceException</issue_title>
<issue_description>### Prerequisites

Write a descriptive title.
Make sure you are able to repro it on the latest released version
Search the existing issues.
Refer to the FAQ.
Refer to Differences between Windows PowerShell 5.1 and PowerShell.

Steps to reproduce

on 7.6.0-preview.5

[System.Management.Automation.CompletionCompleters]::CompleteFilename("") throws NullReferenceException

Expected behavior

should returns CompletionResult

Actual behavior

PS> [System.Management.Automation.CompletionCompleters]::CompleteFilename("")
MethodInvocationException: Exception calling "CompleteFilename" with "1" argument(s): "Object reference not set to an instance of an object."

Error details

PS> Get-Error -newest 1

Exception             :
    Type           : System.Management.Automation.MethodInvocationException
    ErrorRecord    :
        Exception             :
            Type    : System.Management.Automation.ParentContainsErrorRecordException
            Message : Exception calling "CompleteFilename" with "1" argument(s): "Object reference not set to an instance of an object."
            HResult : -2146233087
        CategoryInfo          : NotSpecified: (:) [], ParentContainsErrorRecordException
        FullyQualifiedErrorId : NullReferenceException
        InvocationInfo        :
            ScriptLineNumber : 1
            OffsetInLine     : 1
            HistoryId        : 1
            Line             : [System.Management.Automation.CompletionCompleters]::CompleteFilename("")
            Statement        : [System.Management.Automation.CompletionCompleters]::CompleteFilename("")
            PositionMessage  : At line:1 char:1
                               + [System.Management.Automation.CompletionCompleters]::CompleteFilename …
                               + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
            CommandOrigin    : Internal
        ScriptStackTrace      : at <ScriptBlock>, <No file>: line 1
    TargetSite     :
        Name          : ConvertToMethodInvocationException
        DeclaringType : [System.Management.Automation.ExceptionHandlingOps]
        MemberType    : Method
        Module        : System.Management.Automation.dll
    Message        : Exception calling "CompleteFilename" with "1" argument(s): "Object reference not set to an instance of an object."
    Data           :
        System.Management.Automation.Interpreter.InterpretedFrameInfo, System.Management.Automation, Version=7.6.0.5, Culture=neutral, PublicKeyToken=31bf3856ad364e35 : <ScriptBlock>

    InnerException :
        Type       : System.NullReferenceException
        TargetSite :
            Name          : CompleteFilename
            DeclaringType : [System.Management.Automation.CompletionCompleters]
            MemberType    : Method
            Module        : System.Management.Automation.dll
        Message    : Object reference not set to an instance of an object.
        Source     : System.Management.Automation
        HResult    : -2147467261
        StackTrace :
   at System.Management.Automation.CompletionCompleters.CompleteFilename(CompletionContext context, Boolean containerOnly, HashSet`1 extension)
   at CallSite.Target(Closure, CallSite, Type, String)
    Source         : System.Management.Automation
    HResult        : -2146233087
    StackTrace     :
   at System.Management.Automation.ExceptionHandlingOps.ConvertToMethodInvocationException(Exception exception, Type typeToThrow, String methodName, Int32 numArgs, MemberInfo memberInfo)
   at CallSite.Target(Closure, CallSite, Type, String)
   at System.Dynamic.UpdateDelegates.UpdateAndExecute2[T0,T1,TRet](CallSite site, T0 arg0, T1 arg1)
   at System.Management.Automation.Interpreter.DynamicInstruction`3.Run(InterpretedFrame frame)
   at System.Management.Automation.Interpreter.EnterTryCatchFinallyInstruction.Run(InterpretedFrame frame)
CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
FullyQualifiedErrorId : NullReferenceException
InvocationInfo        :
    ScriptLineNumber : 1
    OffsetInLine     : 1
    HistoryId        : 1
    Line             : [System.Management.Automation.CompletionCompleters]::CompleteFilename("")
    Statement        : [System.Management.Automation.CompletionCompleters]::CompleteFilename("")
    PositionMessage  : At line:1 char:1
                       + [System.Management.Automation.CompletionCompleters]::CompleteFilename …
                       + ~...

</details>

Fixes PowerShell/PowerShell#26277

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Co-authored-by: iSazonov <22290914+iSazonov@users.noreply.github.com>

iSazonov · 2025-10-23T06:14:43Z

@copilot Please move new test to TabCompletion.Tests.ps1 file.

…ts.ps1 Co-authored-by: iSazonov <22290914+iSazonov@users.noreply.github.com>

Copilot · 2025-10-23T06:20:19Z

@copilot Please move new test to TabCompletion.Tests.ps1 file.

Moved the test to TabCompletion.Tests.ps1 as requested in commit 459c0f3.

iSazonov · 2025-10-23T06:47:15Z

@copilot Please remove your comments from the new test.

Co-authored-by: iSazonov <22290914+iSazonov@users.noreply.github.com>

Copilot · 2025-10-23T06:49:56Z

@copilot Please remove your comments from the new test.

Removed comments from the test in commit 534098c.

Copilot

Pull Request Overview

This PR fixes a NullReferenceException thrown when calling CompleteFilename("") with an empty string by adding a null check for context.RelatedAsts before accessing it.

Key Changes:

Added null/empty check for context.RelatedAsts before array indexing
Added fallback to use current provider path when RelatedAsts is null/empty
Added Pester test to verify the fix works correctly

Reviewed Changes

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

File	Description
src/System.Management.Automation/engine/CommandCompletion/CompletionCompleters.cs	Added null check for `context.RelatedAsts` and fallback logic to use current provider path
test/powershell/Host/TabCompletion/TabCompletion.Tests.ps1	Added test case to verify `CompleteFilename("")` doesn't throw exception

Comments suppressed due to low confidence (1)

src/System.Management.Automation/engine/CommandCompletion/CompletionCompleters.cs:1

The else block at line 4598 is paired with the if statement at line 4583, but based on the overall control flow structure, this creates an incorrect nesting. The else block (lines 4599-4602) should be associated with the if statement at line 4583, but there's already a closing brace at line 4598 that closes that if block. This means the else at line 4598 cannot be paired with the if at line 4583. The correct structure should have the else block (4599-4602) immediately follow the closing brace at 4598 without the 'else' keyword on line 4598, or the braces need to be restructured to properly nest the conditional logic.

// Copyright (c) Microsoft Corporation.

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daxian-dbw · 2025-10-23T18:37:12Z

Suppressed by #26291

microsoft-github-policy-service · 2025-10-23T18:37:28Z

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Microsoft Forms

Initial plan

c74e3f2

Copilot AI assigned Copilot and iSazonov Oct 23, 2025

Copilot started work on behalf of iSazonov October 23, 2025 05:50 View session

iSazonov added the CL-General Indicates that a PR should be marked as a general cmdlet change in the Change Log label Oct 23, 2025

Fix NullReferenceException in CompleteFilename and add test

c7a2270

Co-authored-by: iSazonov <22290914+iSazonov@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Fix NullReferenceException in CompleteFilename method~~ Fix NullReferenceException in CompleteFilename when called with empty string Oct 23, 2025

Copilot AI requested a review from iSazonov October 23, 2025 06:02

Copilot finished work on behalf of iSazonov October 23, 2025 06:02

iSazonov mentioned this pull request Oct 23, 2025

Create github copilot setup workflow #26285

Merged

12 tasks

Copilot started work on behalf of iSazonov October 23, 2025 06:15 View session

Move CompleteFilename test from BugFix.Tests.ps1 to TabCompletion.Tes…

459c0f3

…ts.ps1 Co-authored-by: iSazonov <22290914+iSazonov@users.noreply.github.com>

Copilot finished work on behalf of iSazonov October 23, 2025 06:21

Copilot started work on behalf of iSazonov October 23, 2025 06:47 View session

Remove comments from CompleteFilename test

534098c

Co-authored-by: iSazonov <22290914+iSazonov@users.noreply.github.com>

Copilot finished work on behalf of iSazonov October 23, 2025 06:50

iSazonov marked this pull request as ready for review October 23, 2025 06:56

Copilot AI review requested due to automatic review settings October 23, 2025 06:56

iSazonov approved these changes Oct 23, 2025

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Copilot AI reviewed Oct 23, 2025

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iSazonov mentioned this pull request Oct 23, 2025

[System.Management.Automation.CompletionCompleters]::CompleteFilename("") throws NullReferenceException #26277

Closed

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iSazonov marked this pull request as draft October 23, 2025 09:10

daxian-dbw closed this Oct 23, 2025

iSazonov deleted the copilot/fix-nullreferenceexception-filename branch October 24, 2025 03:07

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Fix NullReferenceException in CompleteFilename when called with empty string #26286

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Fix NullReferenceException in CompleteFilename when called with empty string #26286

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