golang/go

x/tools/gopls/internal/analysis/modernize: add pass to use reflect.TypeAssert

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#75422 opened on Sep 11, 2025

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AnalysisFeatureRequestToolsgoplshelp wanted

Description

https://go.dev/cl/702735 replaced v.Interface().(T) with reflect.TypeAssert[T](v), where v is a reflect.Value, and demonstrated a significant performance improvement. Although the new code is 7 chars longer, it is more direct and arguably clearer. We should add a modernizer to automate this transformation when v.Interface().(T) appears in a two-value (x, ok := ...) context in a file using go1.25 or later. The doc comment for TypeAssert states that they are "semantically equivalent".

Contributor guide

Tech stack
go
Domain
developer experiencetooling
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Go programminggopls internalsreflect package
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
Study the existing modernizer passes in x/tools/gopls/internal/analysis/modernize to understand the pattern. Refer to CL 702735 for the implemented transformation. The task is to add a new pass that replaces `v.Interface().(T)` with `reflect.TypeAssert[T](v)` in two value contexts for files using Go 1.25+. Look at how other passes like `loopvar` or `slices` are structured to implement the new pass.