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GeezerVison is showing github.com — Add type inference for $_ in -replace scriptblock by MartinGC94 · Pull Request #28329 · PowerShell/PowerShell

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@MartinGC94

@MartinGC94 MartinGC94 commented Nov 4, 2026 •
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PR Summary

This PR adds type inference for $_ when used inside a scriptblock for the -replace operator.
For example when it's used like this: "123" -replace '2', {[int]$_.Value + 2}

PR Context

Yesterday I found out that you could use a scriptblock for -replace but there was no type inference for $_ in this particular case, so I decided to add it.

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  • This PR is ready to merge. If this PR is a work in progress, please open this as a Draft Pull Request and mark it as Ready to Review when it is ready to merge.
  • Breaking changes
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    • Make sure you've added a new test if existing tests do not effectively test the code changed

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@MartinGC94
Add type inference for $_ in -replace scriptblock
d706bb6
@MartinGC94
MartinGC94 requested review from a team, Patrick Meinecke (SeeminglyScience) and Dongbo Wang (daxian-dbw) as code owners November 4, 2026 14:10
Copilot AI balanced review requested due to automatic review settings November 4, 2026 14:10
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azure-pipelines Bot commented Nov 4, 2026

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Copilot started reviewing on behalf of MartinGC94 November 4, 2026 14:12
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🟡 Changes recommended

Replacement callback detection incorrectly assigns Match to eagerly invoked scriptblocks and misses array-literal callbacks, producing incorrect or missing type inference for $_.

2 open issues
  • Medium severity Infer Match only for the actual replacement callback · New
  • Medium severity Handle array-literal replacement callbacks · New
What changed in this PR

Adds type inference for $_ inside -replace scriptblocks, enabling PowerShell’s inference engine to recognize it as System.Text.RegularExpressions.Match.

Changes:

  • Detects replacement scriptblock contexts for case-sensitive and case-insensitive replacement operators.
  • Adds a regression test for the inferred Match type.
File Description
test/​powershell/​engine/​Api/​TypeInference.Tests.ps1 Tests $_ type inference inside a replacement callback.
src/​System.Management.Automation/​engine/​parser/​TypeInferenceVisitor.cs Adds replacement-context detection and Match inference.

Review effort: Balanced

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Comment thread src/System.Management.Automation/engine/parser/TypeInferenceVisitor.cs Resolved

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Comment thread src/System.Management.Automation/engine/parser/TypeInferenceVisitor.cs Resolved

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@MartinGC94
Fix handling of nested expressions
21922c2
@microsoft-github-policy-service microsoft-github-policy-service Bot added the Review - Needed The PR is being reviewed label Nov 11, 2026
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microsoft-github-policy-service Bot commented Nov 11, 2026

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This pull request has been automatically marked as Review Needed because it has been there has not been any activity for 7 days.
Maintainer, please provide feedback and/or mark it as Waiting on Author

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@daxian-dbw Dongbo Wang (daxian-dbw) Awaiting requested review from daxian-dbw daxian-dbw is a code owner
@SeeminglyScience Patrick Meinecke (SeeminglyScience) Awaiting requested review from SeeminglyScience SeeminglyScience is a code owner

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@MartinGC94
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