golang/go

x/tools/gopls: when editing Go files in GOMODCACHE, offer to clone module and add replace directive

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#77212 opened on Jan 16, 2026

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FeatureRequestToolsgoplshelp wanted

Description

Being able to quickly edit the standard library (e.g. by inserting a print statement) is extremely useful during debugging. However, editing source files from dependencies within the module cache is not as convenient. Gopls could detect an attempt to modify such a file and offer to clone the module, add a replace directive to the main module, and move the cursor to the corresponding position in the cloned file, which can then be freely edited. The replace directive could be flagged with a // FIXME: debugging comment, with a code action to revert it.

(Credit to @prattmic for the idea.)

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.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Go programming languageGo modulesgopls internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20
Research direction
Start by understanding how gopls handles file saves and detects modifications. Look at the gopls module cache handling in internal/lsp/cache/ and the go.mod parser for replace directives. The issue suggests offering a code action when editing a file in GOMODCACHE; investigate existing code actions in internal/lsp/command/ and how they modify go.mod. Also review how gopls currently handles the workspace folder and module graph to clone the module and add the replace directive.