golang/go

cmd/go: test -coverprofile should ask compiler to drop (incorrect) position information

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#67,938 opened on Jun 11, 2024

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GoCommandNeedsFixgabywinshelp wanted

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Description

% cat x.go
package p

func f(int) string

func g() {
	b := f(1)
	collect := func(min, max, stop int) []int {
		return nil
	}
	b := f(2)
	_ = collect
}
% go test -coverprofile=c.out x.go
# command-line-arguments
./x.go:6:2: `b' declared and not used
./x.go:10:35: no new variables on left side of :=

There is no column 35 on the line b := f(2), making the error message very confusing. The problem is that cover has inserted text into the lines. When the compiler did not print column information, that was invisible. Now it's not.

To make it invisible again, the compiler should add a flag to drop position information, and then the go command should use that flag when compiling with test coverage.

Contributor guide

Research direction
Understand how the Go compiler handles position information during test coverage. Trace the code path where cover injects additional text and how the compiler emits position information. Then propose a compiler flag to omit position information and modify the go command to set that flag when compiling with coverage.
Tech stack
go
Domain
compilerstooling
Issue type
Bug
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.
1-2 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
Gocompiler internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20